UWORLD

empirical vs molecular formula

Empirical Formula: The simplest whole number ratio of atoms in a compound Molecular Formula: (empirical formula)n where n is an integer, to determine this you must know molar mass Molecular formula = empirical formula * (molar mass/empirical mass)

Complex III

In complex III, UQH2 then passes the electrons to oxidized cytochrome C (cyt-Cox), yielding reduced cytochrome C (cyt-Cred) and regenerating UQ. Finally, cyt-Cred passes its electrons to oxygen, yielding water and regenerating cyt-Cox.

Northen Blotting

RNA is isolated from the tissue and denatured. The RNA is separated by size via gel electrophoresis. The RNA samples are transferred from the gel to a blotting membrane and immobilized. The membrane is incubated with a labeled RNA or single-stranded DNA probe complementary to the RNA sequence of interest. If the sequence of interest is present, the probe binds to it (ie, hybridizes) and the label (eg, radioactive atom, fluorescent dye) allows visual detection of the probe. The sample is washed to remove unbound probes. Researchers determine if a visual signal is present. A visual signal indicates that hybridization occurred, meaning the RNA sample contains the RNA sequence of interest. The lack of a visual signal corresponds to an absence of the target RNA sequence.

Bisphosphoglycerate mutase converts 1,3-bisphosphoglycerate into 2,3-bisphosphoglycerate, which allosterically regulates hemoglobin. It decreases oxygen affinity by stabilizing the deoxyhemoglobin conformation. Increasing concentrations of 2,3-bisphosphoglycerate produce a ---- shift in the oxyhemoglobin dissociation curve and favor oxygen delivery to tissues

right

Under -------------------, enzymatic activity is directly proportional to kcat because the enzyme is operating at its maximum velocity Vmax. Because Vmax is also directly proportional to enzyme concentration [E], an increase in [E] will proportionally increase Vmax, and therefore increase the total product output.

saturating conditions ([S] >>Km),

Noncovalent interactions between amino acid backbone groups are primarily found in _______ structural elements.

secondary

Lysosomal pH

5

Imine

A double bond between a carbon and a nitrogen

Rough ER

A network of interconnected membranous sacs in a eukaryotic cell's cytoplasm; covered with ribosomes that make membrane proteins and secretory proteins. Ribosomes synthesize proteins in either the "free" state in the cytoplasm or the "bound" state when attached to the rough endoplasmic reticulum (ER). For proteins that enter the ER (eg, secretory proteins), a signal sequence within the target mRNA bound to the ribosome is translated into a signal peptide that induces transport of the ribosome-mRNA complex to the rough ER. The complex synthesizes proteins into the lumen of the rough ER, which then

Nucleotide structure

A nucleoside is a pentose (five-carbon) sugar linked to a nitrogenous base on the 1′ carbon by a covalent glycosidic bond. Nucleotides consist of a nucleoside attached to one or more phosphate groups by a phosphoester bond. If the pentose has a hydroxyl group at the 2′ carbon, it is ribose; if only a hydrogen is present at the same position, it is deoxyribose.

Sphingomyelin

A sphingophospholipid containing a sphingosine backbone and a phosphate head group.

Conjugation

A temporary union of two organisms for the purpose of DNA transfer.

In a concentration cell, the anode and the cathode are both made of the same metal and are surrounded by the same ionic solution, but the solutions differ in concentration. As a result, the same half-reaction occurs in opposite directions at both electrodes.

Accordingly, concentration cells produce a flow of electrons caused by the drive to equalize the ion concentrations in the two half-cells. In the less-concentrated half-cell, cations are made (ie, by oxidizing metal atoms), and in the more-concentrated half-cell, cations are consumed (ie, by reduction) until the cation concentrations in each half-cell are equal. As such, electrons flow from anode to cathode until both cells have the same Ni2+(aq) ion concentration, at which point the reaction stops.

Lowest oxygen consumption means what in terms of ADP/ATP ratio in the ETC?

Aerobic organisms primarily generate ATP using energy provided by the electron transport chain (ETC). The final step in the chain is reduction of oxygen to water, and the rate of oxygen consumption can be used as a measure of ETC activity. Higher ETC activity corresponds to a higher ATP/ADP ratio or a lower ADP/ATP ratio.

Annyhydride

An anhydride is a carboxylic acid derivative formed from a carboxylic acid and an acid chloride, or the condensation of two carboxylic acids.

Imine Formation

An imine is an analogue of ketones and aldehydes that contains a carbon-nitrogen double bond. Imines are formed from a ketone or aldehyde and NH3 or a primary amine via an acid-catalyzed addition of the amine followed by an acid-catalyzed dehydration.

AV vs semilunar valves

Atrioventricular (AV) valves allow blood to flow from the atria to the ventricles, and semilunar valves allow blood to flow from the ventricles into the arteries.

Avogadro's law

Avogadro's law states that the volume occupied by a gas is directly proportional to its number of moles if the temperature and pressure are constant. When two gases at the same temperature and pressure are compared, the gas with more moles occupies the larger volume.

water soluable vitamins are

B and C

Chaperone Protien

Chaperones are a class of proteins that help other proteins fold correctly. They decrease the tendency of a protein to aggregate and increase its solubility.

negative control

Control group where conditions produce a negative outcome. Negative control groups help identify outside influences which may be present that were not accounted for when the procedure was created.

Covalent bonds between amino acid backbone groups (ie, the non-side group portion of amino acids) are _____ bonds and are the basis for primary protein structure (ie, amino acid sequence).

Covalent bonds between amino acid backbone groups (ie, the non-side group portion of amino acids) are peptide bonds and are the basis for primary protein structure (ie, amino acid sequence).

cytoskeletal filaments are found in the cytoplasm

Cytoskeletal filaments are found in the cytoplasm of cells and can interact directly with various components of the cell membrane (eg, by anchoring membrane proteins in place). However, they are not themselves part of the plasma membrane.

Electron capture

Electron capture is a special form of beta decay in which a nucleus absorbs an electron from an external source without emitting a particle. The absorbed electron converts a proton into a neutron, decreasing the atomic number by one. think beta positive

Electronegativity

Electronegativity is the tendency of an atom to attract electrons within a bond. The electronegativity of an atom depends on the distance of the valence electrons from the nucleus (ie, Coulomb's law) and on how well the core electrons shield the valence electrons from the nucleus (ie, the effective nuclear charge). On the periodic table, electronegativity tends to increase from left to right across a period (row) and from bottom to top in a group (column).

Esters are named by stating the alcohol chain prefix followed by the name of the carboxylic acid, with the suffix_____ acid replaced by _____

Esters are carboxylic acid derivatives formed by Fisher esterification, an acid-catalyzed reaction of a carboxylic acid and an alcohol. Esters are named by stating the alcohol chain prefix followed by the name of the carboxylic acid, with the suffix -ic acid replaced by -ate

Bacteria, Eukarya, Archaea

Eukaryotic organisms are classified into the Eukarya domain, but prokaryotic organisms are in either the Bacteria or the Archaea domain.

Exocytosis

Exocytosis, which requires energy (eg, ATP), is a form of membrane transport by which secretory vesicles within a cell fuse with the plasma membrane, allowing for the release of their contents into the extracellular environment.

Zeff between O and F. Which is higher?

F

gap junctions

Gap junctions are cell-cell junctions that mediate communication between cells. Protein channels (connexons) in one cell align with complementary channels in another cell to form pores that facilitate the passive and bidirectional exchange of ions and small solutes. Gap junctions are found in cell populations that depend on coordinated activity, such as smooth muscle, cardiac muscle, or neural tissue.

positive control

Group expected to have a positive result, allowing the researcher to show that the experimental set up was capable of producing results.

If a sample were to have a rotation of zero, what does that mean?

If a sample were to have a rotation of zero, it would mean that the rotations have canceled each other out. This occurs when the sample is a 50:50 mixture of enantiomers (ie, 50% R and 50% S) known as a racemic mixture.

Leptin and Ghrelin

In an energy-rich state (eg, after a meal), leptin is released by white adipocytes to trigger appetite suppression via the hypothalamus. In contrast, in an energy-poor state, ghrelin is released by stomach gastric cells to trigger hunger and food-seeking behavior via the hypothalamus

Infrared Spectroscopy

In infrared (IR) spectroscopy, a sample is irradiated with IR light, and a spectrometer detects and records the percentage of radiation that passes through the sample over a range of frequencies. Different functional groups absorb IR radiation at different intensities and different frequencies, and therefore the signal from each group appears in a particular region of the IR spectrum. The absorption frequency for a particular functional group depends on the types of bonds present. Characteristic functional group absorptions include: 3650-3200 cm−1 (O-H stretch) 3300 cm−1 (sp C-H stretch) 3100 cm−1 (sp2 C-H stretch) 3000 cm−1 (sp3 C-H stretch) 1810-1650 cm−1 (C=O stretch)

N-linked carbohydrate chains

N-linked carbohydrate chains are added to certain asparagine residues of proteins in the endoplasmic reticulum.

Is muscle a connective tissue?

NO!!!! Muscle tissue, classified into three types, is under the control of the nervous system and allows for movement. Although connective tissue comes into contact with muscle tissue, muscle is not considered to be a type of connective tissue.

Does alternative slicing increase genetic variation?

No because the genome is not altered, but it increases protien diversity

ionizable side chains

Of the 20 proteinogenic amino acids, 7 have side chains that can be ionized at certain pH levels between 0 and 14. These 7 amino acids (R, K, Y, C, H, E, D) are collectively referred to as the ionizable amino acids. Each ionizable amino acid has a characteristic titration curve, with buffer regions surrounding the pKas of the C-terminus, the N-terminus, and the side chain

Determining velocity from position vs time graph. Which point has a greatest velocity?

Point b because the slope is greatest

Primary vs Secondary Transport

Primary (direct) active transport uses the energy released by ATP hydrolysis (performed by a transmembrane ATPase). Secondary (indirect) active transport is a coupled transport process that uses the energy released by the movement of one substance along its concentration gradient (passive transport) to move another substance against its concentration gradient. Essentially, the potential energy stored in the concentration gradient of one molecule is used for the transport of another molecule.

If the highest number stereo center is R then the molecule is

R

acyl group

R-C=O

Ribosomes Free State vs Bound State

Ribosomes, composed of specific proteins and ribosomal RNA (rRNA), are molecular protein-synthesis machines common to all cell types. During translation, ribosomes read messenger RNA (mRNA) sequences to synthesize encoded proteins. In eukaryotic cells and prokaryotic cells, ribosomes exist in the "free" state in the cytoplasm. However, in eukaryotic cells only, ribosomes can exist in the "bound" state, where they are attached to the rough endoplasmic reticulum

Sugars are classified as L or D based on the configuration of the highest numbered chiral carbon (the anomeric carbon)

S = L sugar R = D sugar

Several types of neuroglia exist in the central nervous system (CNS):. What are they

Several types of neuroglia exist in the central nervous system (CNS): Ependymal cells: line compartments and produce cerebrospinal fluid (Choice A). Oligodendrocytes: form myelin sheaths around axons to reduce ion leakage, decrease capacitance, and increase action potential propagation speed along the axon. Microglia: serve as immune cells which phagocytize pathogens, damaged cells, and waste materials (Choice C). Astrocytes: contact blood vessels, regulating blood flow to coordinate synaptic activity and chemical changes. These cells are also important in maintaining extracellular fluid, ion, pH, and neurotransmitter homeostasis. In addition, astrocytes provide nutrients necessary for neuron function and are thought to play a role in neuronal development, maintenance, and communication with other glial cells (Choice D).

Bone marrow

The bone marrow is a soft, spongy tissue that lines the inside of bones and gives rise to most cells involved in the immune response. Cells originating in the bone marrow begin as multipotential hematopoietic stem cells and can differentiate into lymphoid or myeloid progenitor cells. Lymphoid progenitor cells go on to become B cells, T cells, or natural killer cells. Myeloid progenitor cells in the bone marrow further differentiate into erythrocytes, platelet-producing megakaryocytes, neutrophils, basophils, eosinophils, monocytes, or mast cells.

The cardiac sphincter

The cardiac sphincter (ie, lower esophageal sphincter) is a muscular ring located at the junction of the esophagus and the stomach that controls the passage of food into the stomach.

cell wall

The cell wall is a rigid polysaccharide layer surrounding the cell membrane that provides protection and structural support in certain cell types. Most prokaryotic cells have cell walls, but only some eukaryotic cells (ie, plants, fungi) have them.

Electric Force on a charged object equals the product of the objects charge q and the electric field E

The electric force FE on a charged object equals the product of the object's charge q and the electric field E: An electric field exists when there is a difference in the electric potential (ie, voltage) ΔV between two locations. The component of the electric field in a given direction (eg, the y-direction) equals the ΔV per unit of distance

Fluidity of the cell membrane

The fluidity of a cell membrane is largely dependent on the lengths of the fatty acyl tails in the bilayer and on the number of double bonds in each tail. Short chains with double bonds yield the highest fluidity because they participate in the fewest intermolecular interactions with neighboring lipids.

kidney function

The kidneys' primary function is to maintain the salt and water balance of the blood. They also play a key role in regulating multiple aspects of physiological homeostasis (eg, blood pressure, waste removal, osmolarity, blood pH, erythrocyte production).

peritoneum vs peritoneal cavity

The peritoneum comprises two tissue membranes that line the abdomen: the parietal layer, which lines the abdominal wall, and the visceral layer, which covers the abdominal organs. The peritoneal cavity is a potential space (ie, an area between two adjacent structures that may press together) between the parietal and visceral layers of the peritoneum. The peritoneal cavity is found within the abdomen and contains organs such as the liver, stomach, and intestines.

Pauli Exclusion Principle

The quantum state of all electrons around an atom can be described using four quantum numbers (n, ℓ, mℓ, ms): The principal quantum number n describes the main energy level (shell) of the electron and its most probable distance from the nucleus (n = 1, 2, 3, 4...). The orbital angular momentum quantum number ℓ corresponds to the subshell type (s, p, d, f) and the corresponding shape of the orbital occupied by the electron, where ℓ = 0, 1, 2, 3, 4, ..., (n − 1). The magnetic quantum number mℓ determines the number of orbitals of a given type and their orientations within a sublevel. For a given orbital, the values of mℓ include all integers ranging from −ℓ to +ℓ. The electron spin quantum number ms describes the angular momentum of an electron, which is a vector quantity with a magnitude of ½ and a direction that is either spin up (positive) or spin down (negative). The Pauli exclusion principle states that each orbital subshell can hold a maximum of two electrons, but two electrons in the same orbital must have opposite spins. Therefore, the two electrons in the 4s orbital of a calcium atom must have opposite spins of +½ and −½.

Hydrogen bonding and metling temperature

The strands of a DNA double helix are held together by intermolecular interactions that include hydrogen bonds. Reducing the number of hydrogen bonds decreases the melting point of a double helix.

subcutaneous layer

The subcutaneous layer (hypodermis) is composed of adipose cells that insulate the body, epidermal melanocytes prevent UV radiation from damaging the DNA of cells, keratinized derivatives of skin help protect the body from external injury, and dermal sweat glands secrete sweat onto the skin surface to regulate body temperature.

work-energy theorem

The work done on an object equals the change in kinetic energy of the object

alpha Bromoacid formation

The α-carbon of a carboxylic acid is the carbon adjacent to the carbonyl carbon and can undergo substitution reactions to form α-substituted carboxylic acids. An α-bromoacid is a carboxylic acid with bromine on the α-carbon and is formed when a carboxylic acid is reacted with PBr3, Br2, and then H2O.

van der Waals forces

Van der Waals forces are noncovalent interactions between the dipoles of two neutral molecules. Van der Waals forces include: Dipole-dipole interactions (ie, attractions between two permanent dipoles) Dipole-induced dipole interactions (ie, attractions between a permanent dipole and an induced dipole) London dispersion forces (ie, attractions between two induced dipoles)

state function

a property of the system that changes independently of its pathway

thin layer chromatography

a separation technique that involves the separation of small molecules as they move through a silica gel TLC can be used to determine whether starting material is still present and whether desired products and/or side products have formed

Cholesterol and its hormone derivatives are classified as _______ molecules because they contain a hydrophilic region and a hydrophobic region, which allows them to diffuse across cell membranes.

amphipathic

Archimedes' Principle

an object in a fluid experiences a net upward directed buoyant force Fb equal to the product of the fluids density Pfl, the gravitational acceleration g and the volume of the fluid displaced by the object

The law of conservation of mass

atoms are neither created nor destroyed, they can only be rearranged

Positron emission

beta positive decay

The large intestine is composed of the

cecum, colon, and rectum.

Pyruvate decarboxylase

converts pyruvate to acetaldehyde as the first step in the production of ethanol by yeas

lactone

cyclic ester

Protons flow into the mitochondrial matrix through ATP synthase. Increased ATP synthase activity would result in more protons flowing into the matrix, which would-----the pH.

decrease

When is the collecting duct relatively impermeable to water?

during times of hydration

In normal phase TLC, nonpolar compounds have less affinity for the polar stationary phase than polar compounds, and therefore travel _____

farther up the plate. A polar compound will have a smaller Rf value than a nonpolar compound.

FMN structure

flavin mononucleotide

phospholipid structure

glycerol + 2 fatty acids + phosphate group

Based catalyzed aldol reaction

https://www.youtube.com/watch?v=nq_gBOwf6mw&t=283s

What preceds the cecum?

illeium

zymogen

inactive form of an enzyme

cyclic amides are

lactams

if a compound has a strong interaction w/ the mobil phase that means it is in TLC

less polar, i.e travels farther in TLc

VESPER

memorize

When zero net force is exerted on an object, the object must be at rest or moving at a constant velocity

newtons first law of motion implies that objects within inertia (i.e mass) resist changes in their velocity. Hence objects at rest remain at rest and objects in motion remain in motion with constant velocity unless a net external force is exerted upon them

post-translational modification

non amino acid additions to proteins

Cholesterol is found in eukaryotes but not

prokaryotes

If both anomeric carbons are involved in the glycosidic bond that means that the sugar is not

reducing

Microarray

shows which genes are being actively transcribed in a sample from a cell

The freezing point of a substance is determined by the strength and extent of intermolecular forces acting between molecules. These interactions are affected by the presence of solutes. As a colligative property, the extent of freezing point depression of a solution is a function of the amount of _____ added.

solute

Genetic mutations that inhibit gluconeogenesis and glycogenolysis can prevent effective hormonal control of blood glucose levels. Dietary supplementation with a glucose source such as ____ can help maintain glucose levels in these cases.

startch

the change in velocity of an object over time =

the acceleration of the object

covalent catalysis

the active site contains a nucleophile that is briefly covalently modified

Alpha D Fructose vs B D fructose. Where is the anomeric carbon on fructose?

the anomeric carbon on the 2nd

The objects weight W in a fluid eyqlas

the product of the objects density pobj, g and the volume of the object V obj

Calcitonin, a hormone synthesized by the_____ gland, decreases calcium concentrations in the blood by inhibiting osteoclast activity (bone resorption) and promoting calcium excretion in the kidneys.

thyroid

All peptide bonds are planer due

to partial double bond character and resonance

surface tension and water

, surface tension is a force induced at the interface between a liquid and a gas. The molecules in the liquid interact with each other more strongly than they interact with molecules in the air, causing the surface of the liquid to behave as a thin film. Water has a high surface tension, but this characteristic does not aid in water's ability to act as a solvent

second order reaction

-rate is proportional to either the concentrations of 2 reactants or to the square of the concentrations of a single reactant *Rate = k[A]1[B]1 or rate = k [A]2 or rate = k [B]2 1/([A]) vs time line slope = k

Exothermic Hydrolysis of ATP

ATP hydrolysis releases thermal energy (ie, it is exothermic) because the energy released by bond formation exceeds the energy consumed by bond breaking during the reaction. ATP hydrolysis involves both bond cleavage and bond formation (ie, the P-O bond is not cleaved in isolation), and the reaction is exothermic because the energy released by forming the new bonds exceeds the energy consumed by breaking the old bonds in both ATP and water.

When the temperature is high enough for the vapor pressure to equal the ambient pressure, the liquid boils.

Ambient atmospheric pressure is not affected by whether or not a liquid contains solutes, so the liquid must reach the same vapor pressure to boil regardless of the presence or absence of solute The addition of solute lowers the vapor pressure of a solution at all temperatures, and therefore raises the temperature required for the vapor pressure to become equal ambient pressure and begin to boil (the boiling point).

amino acid catabolism

Amino acid catabolism (degradation) involves the removal of nitrogen from backbones and certain R-groups in the form of ammonia, which is detoxified and prepared for excretion by the urea cycle: The nitrogen of amino acid backbones is removed by transamination and deamination (removal of an amine to produce a ketone), producing α-keto acids in the process. The side chains of asparagine and glutamine contain amides, which are functional groups consisting of a nitrogen atom linked to a carbonyl carbon. Amides are catabolized by deamidation rather than deamination. Deamidation releases ammonia from an amide instead of an amine; the result of deamidation (eg, of Asn or Gln side chains) is replacement of the amide with a carboxylic acid, whereas the result of deamination (eg, of the backbone α-amine of any amino acid) is replacement of the amine with a carbonyl oxygen. Among the answer choices, only glutamine contains an amide group and can therefore produce ammonia through deamidation.

SN1 vs SN2 reaction

An SN1 reaction occurs in two steps whereas an SN2 reaction occurs in a single step. The first step of an SN1 reaction involves formation of a carbocation intermediate when the bond between the leaving group and the adjoining carbon is broken. In the second step, the nucleophile adds to the carbocation, forming the product of the reaction.

According to Hess's Law, Heat of reaction can be calculated by

Bond enthalpy (ΔH°) is the amount of energy needed to break 1 mole of a bond between two atoms in the gas phase. Energy is absorbed (ΔH° > 0) when a bond is broken, and energy is released (ΔH° < 0) when a bond is formed. Hess's law states that the standard enthalpy change (ΔH°rxn) of a reaction is equal to the sum of the enthalpy changes for each step involved in bond breakage and formation during a reaction

Transamination and Deamination of AA

Catabolism is the breakdown of large molecules into smaller units and leads to production of energy in the form of ATP. Protein catabolism in the liver refers to the breakdown of polypeptide chains and proteins into individual amino acids, which can be further metabolized to enter the citric acid cycle and produce ATP. This requires a transamination reaction that removes the amino group (−NH3+) from the carbon backbone of the amino acid. The transamination reaction produces an α-keto acid from the amino acid by transferring the −NH3+ group to α-ketoglutarate, forming glutamate. The glutamate produced in this process is then deaminated, releasing ammonia (NH3), which enters the urea cycle. The urea formed in this cycle is released in urine.

Convergent vs Parallel vs Divergent

Convergent evolution leads to similar characteristics in distantly related species that are exposed to similar environmental pressures. Parallel evolution also leads to similar characteristics in species found in similar environments but occurs in species with a more recent common ancestor. Divergent evolution leads to unique characteristics in somewhat closely related species that face contrasting environmental pressures.

Disruption of slat bridges during histone acetylation

DNA winds tightly around proteins referred to as histones to form structural units known as nucleosomes. Gene expression depends partially on the association of histones with DNA. Genes that are actively transcribed are found on unwound stretches of chromatin called euchromatin, which transcription machinery can easily access. Inactive genes are usually in highly condensed DNA known as heterochromatin, which is much less accessible. Covalent post-translational modifications such as methylation, acetylation, and phosphorylation alter the association of histones with DNA. DNA is predominantly negatively charged due to the phosphate groups on the backbone. Histones associate with DNA by forming salt bridges between positively charged amino acid residues and negatively charged phosphate groups. These ionic interactions allow histones to bind tightly to DNA and prevent genes from being transcribed. Acetylation of histones involves the transfer of acetyl groups from acetyl coenzyme A to positively charged amino groups on lysine or arginine residues. This modification disrupts salt bridges by reducing the positive charge on histones, which allows DNA to unwind and become more accessible to transcription machinery. As a result, the acetylation of histones causes nucleosomes to relax and increases gene expression

Desmosomes

Desmosomes provide tensile strength to epithelial cell sheets by anchoring the cytoskeletons, specifically the intermediate filaments, of two cells together. This creates a continuous cytoskeletal network that spans the entire epithelial sheet, one through which mechanical stress (eg, pulling, stretching, tension) can be distributed. Desmosomes are found predominantly in tissues that are subject to high levels of mechanical stress (eg, muscle tissue, epithelial layers of the skin) and prevent tissue tearing

Cori-Anderson Cycle

During glycolysis, NAD+ is converted to NADH by the enzyme glyceraldehyde-3-phosphate (GAP) dehydrogenase. For glycolysis to continue, NAD+ must be regenerated. Under aerobic conditions, electrons from NADH can be transferred to the electron transport chain (ETC) and ultimately to oxygen. However, in anaerobic conditions, NAD+ cannot be regenerated by the ETC because there is insufficient oxygen to accept electrons. Consequently, NADH donates electrons to pyruvate, which is reduced to lactate in the process. Lactate that builds up from this mechanism must be removed from the system because it can lead to muscle pain and nausea. The lactate in muscles enters the bloodstream, which carries it to the liver. In the liver, lactate is converted to glucose during gluconeogenesis and is carried back to muscles by the blood. The process of carrying lactate from the muscle to the liver and moving regenerated glucose from the liver back to muscles is called the Cori cycle, which connects gluconeogenesis and glycolysis.

Transamination

During the first step in oxidative degradation, amino acids undergo a transamination reaction that separates the amino group from the carbon skeleton. The amino group is subsequently converted to the end product urea in a series of reactions known as ureagenesis, whereas the carbon skeleton (an α-keto acid) can be directed to one of several fates, including gluconeogenesis, ketogenesis, or oxidation in the citric acid (Krebs) cycle.

Histone acetylaiton vs Histone deacetylation

During the initial steps of DNA packaging, the DNA double helix wraps twice around a bead-like octamer complex known as the histone core. This DNA-histone complex, also called chromatin, can undergo specific chemical modifications that allow it to exist in two different conformations: the closed conformation (heterochromatin) and the open conformation (euchromatin). Histones have tails (ie, N-termini protruding outward) that are accessible to modifying enzymes, which add or remove chemical groups to change chromatin structure and induce or repress gene expression. For example, histone acetylation, in which acetyl groups are added to histone tails, is catalyzed by the enzyme histone acetylase. Histone acetylation promotes gene transcription by loosening heterochromatin into euchromatin, making the DNA region readily accessible to the transcription machinery. Conversely, histone deacetylase enzymes downregulate gene expression by removing acetyl groups from histones, which reverts euchromatin back to heterochromatin, restricting transcriptional access to specific genes. Histone deacetylase inhibitors, such as valproic acid (VA), prevent removal of acetyl groups by histone deacetylases. As an SMA drug, VA improves motor neuron survival by making the genomic region containing SMN2 more accessible to RNA polymerase and transcription factors, thereby increasing SMN2 expression (ie, producing more FL-SMN and SMNΔ7)

Serine and Threonine have what types of alcohols

Each amino acid has a unique side chain that can be characterized by its functional groups. Serine and threonine have primary and secondary alcohols in their side chains, respectively.

Enzymatic reactions typically behave as _____ -order or_____-order reactions.

Enzymatic reactions typically behave as zero-order or first-order reactions. In zero-order reactions, the rate is only dependent on the rate constant kcat because substrate concentrations exceed the Km value. First-order reactions depend on substrate concentration and occur when Km is greater than the substrate concentration.

Epithelial cells

Epithelial cells are packed together tightly into sheets that make up the outer layer of the skin (the epidermis), the secretory components of glands, and the lining of the inner cavities of the body (eg, the lumen of hollow organs such as the gastrointestinal tract). Endothelial cells are a specialized type of epithelial cell that line the inside of the heart, blood vessels, and lymph vessels specifically. However, endothelial cells do not line the lumen of the gastrointestinal tract.

However, in some cases two species may be unable to produce hybrid embryos, or hybrids may be inviable (unable to survive) or infertile. The inability of two species to produce viable or fertile hybrid offspring is called reproductive isolation, which may be prezygotic (before zygote formation) or postzygotic (after zygote formation)

Failure of sister chromatids to segregate properly (eg, due to chromosomal nondisjunction) during embryonic mitosis generates cells containing missing or extra genetic information. Accordingly, the ability of these cells to divide and differentiate into functional somatic cells in the embryo would be impaired. This would inhibit zygote development and likely cause early embryonic death.

Gastric juice

Gastric juice is a digestive fluid primarily composed of hydrochloric acid (HCl), which is secreted by parietal cells in the stomach. Gastric juice is a highly acidic solution that maintains the stomach lumen at a low pH of 1-3; this acidic environment is required for protein digestion (via activation of proteolytic enzymes) and to kill harmful bacteria. After sufficient churning, the stomach expels a semifluid mass of partially digested food mixed with gastric juice, known as chyme. The highly acidic chyme passes into the duodenum, where it is neutralized by the bicarbonate ions secreted from the pancreas via the pancreatic duct and the alkaline bile released from storage in the gallbladder. As a result, the pH of the chyme is increased to ~6

Hydrolysis of a glycosidic bond is cleavage of the linkage by addition of _____ breaking the molecule into two smaller units.

H2O

heme

Heme is a common cofactor found in many proteins, and it is required for oxygen binding in hemoglobin and myoglobin. The characteristic structure of heme is a porphyrin ring with a central iron (Fe) atom. The passage states that myoglobin contains heme and that when EBB is added, myoglobin releases its heme cofactor. Of the given options, only Choice D shows a porphyrin ring with an iron center. Therefore, this diagram must depict the structure of the cofactor released when EBB is added to myoglobin.

Blood glucose levels are normally maintained within a narrow range by the opposing effects of insulin and glucagon. Explain

High blood glucose stimulates insulin release. Insulin decreases blood glucose concentration by inhibiting glucagon release, promoting glucose uptake by insulin-responsive tissues (ie, adipose, muscle), and decreasing hepatic glucose production (eg, gluconeogenesis). Insulin also stimulates glycogen synthesis (liver, muscle), triglyceride synthesis (via glucose transport into adipocytes), and protein synthesis (via entry of plasma amino acids into tissues). Low blood glucose stimulates glucagon release. Glucagon increases blood glucose levels by promoting production of gluconeogenic substrates and by stimulating glycogen breakdown (glycogenolysis) and hepatic gluconeogenesis. Glucagon limits glucose use by insulin-sensitive tissues and decreases glucose uptake by peripheral tissues. Low blood glucose has also been shown to promote the release of epinephrine, a hormone that stimulates glucagon release

Why is hydrogen bonding so strong?

Hydrogen bonding is one of the stronger intramolecular and intermolecular forces, and it is stronger than other types of dipole-dipole attractions. This strength is due to the large dipole moments involved as well as the small size of the hydrogen atom. This small size allows the partially positive hydrogen to be closer to a partially negative atom, which creates a stronger attraction.

Isoelectric focusing

In isoelectric focusing, an electric field causes proteins to migrate through a pH gradient. The low-pH end of the gradient is placed near the anode and the high-pH end is placed near the cathode. As proteins migrate from low pH to high pH (from anode to cathode), they lose protons and become less positively charged, stopping when their net charge becomes zero. The opposite is true of proteins migrating from high pH to low pH.

Nonbonding electron transition

In the ground state, π electrons from double bonds are in the π bonding molecular orbital, and nonbonding electrons (ie, lone electron pairs) are in the n nonbonding molecular orbital. The nonbonding molecular orbitals are higher in energy than the π bonding molecular orbitals. Upon interactions with UV light of sufficient energy, π and nonbonding electrons are excited to the Lowest Unoccupied Molecular Orbital (LUMO), called the π* antibonding orbital. These excitations are described as a transition from the lower energy bonding molecular orbital to the higher energy antibonding orbital in the form of π → π* or n → π*, depending on whether a π or n electron is excited.

arrector pili muscles in hot and cold

In this scenario, the controls are exercising in a hot environment, so the arrector pili muscles (attached to hair follicles in the skin) would not contract. However, in cold environments, sympathetic signaling causes contraction of the arrector pili muscles, which causes piloerection (ie, hairs standing upright). Piloerection, which impedes heat loss by trapping heat near the skin surface, is not an efficient means of heat retention in humans due to insufficient body hair.

B oxidation

In β-oxidation, a carnitine transporter moves fatty acids from the cytosol into the mitochondria. However, the presence of AMPK phosphatases would inhibit β-oxidation. Instead, fatty acid synthesis requires shuttling of citrate from the mitochondria into the cytosol to yield the acetyl-CoA precursor.

Acid catalyzed tautomerization

Keto-enol tautomerization is a base- or acid-catalyzed isomerization that converts a ketone or aldehyde into an enol. Tautomerism involves a proton transfer from the α-carbon of a ketone or aldehyde to the carbonyl oxygen atom along with pi bond migration. The keto and enol tautomers are in equilibrium and are classified as constitutional isomers.

Enamine Formation

Ketones and aldehydes react with primary (1°) and secondary (2°) amines to form a carbon-nitrogen bond. The reaction begins with an acid-catalyzedaddition of the amine to the carbonyl, which involves protonation of the carbonyl, nucleophilic attack of the carbonyl by the amine, and deprotonation of the amine. This forms an intermediate known as an α-aminoalcohol. The second part of the reaction is an acid-catalyzed dehydration involving protonation of the -OH group, loss of H2O, and deprotonation. The product formed is dependent on the type of amine used (1° or 2°). If a 1° amine is used, an imine (nitrogen analogue to ketones and aldehydes) is formed because the nitrogen has a proton available for removal in the last step, permitting C=N bond formation. If a 2° amine is used, an enamine (nitrogen analogue to an enol) is formed because the nitrogen does not have a proton available to be removed in the last step. Therefore, a proton is removed from the α-carbon, forming a C=C bond.

lactate synthesis

Lactate synthesis is coupled to the synthesis of NAD+ from NADH. Under anaerobic or oxygen-poor conditions, this process provides the NAD+ necessary to continue glycolysis.

Protien denaturation is caused by

Likewise, protein denaturation (unfolding) is commonly driven by amphipathic molecules (ie, molecules containing both hydrophilic and hydrophobic regions) that disrupt the energetically favorable hydrophobic interactions between amino acids in the interior of the protein. This is due to the hydrophobic effect: In the absence of denaturant molecules, the "hiding" of hydrophobic residues in the interior of the protein allows water molecules surrounding the protein to adopt a much higher entropy state, resulting in an overall large, negative Gibbs free energy of folding. In contrast, formation of hydrogen bonds between two polar side chains is at best only slightly more energetically favorable than those same side chains forming hydrogen bonds with water. Consequently, although such hydrogen bonds may help stabilize folded protein structure, they are not the primary factor in protein folding itself.

Hydrolyzable lipids vs nonhydroyzable lipids

Lipases are enzymes that digest certain emulsified lipids to facilitate their absorption, although some lipids are nonhydrolyzable. Hydrolyzable lipids contain ester bonds that can be cleaved by lipases through the addition of a water molecule (hydrolysis). These lipids include triacylglycerols, phospholipids, sphingolipids, and waxes. Nonhydrolyzable lipids do not contain the ester linkages necessary for lipase digestion. The most common nonhydrolyzable dietary lipids are cholesterol (steroids) and fat-soluble vitamins (A, D, E, and K).

lipid processing

Lipid processing begins in the small intestine (duodenum), where bile salts break down lipid globules into smaller droplets in a process called emulsification. This process results in the formation of spherical structures known as micelles, which are composed of a hydrophobic core containing the nonpolar hydrocarbon tails of lipids and an outer shell of polar head groups that make contact with water. The formation of micelles increases the surface area of lipids available for hydrolysis by lipases.

London dispersion forces

London dispersion forces (also called induced dipole-induced dipole interactions) are a weak mutual attraction resulting from the formation of instantaneous dipoles induced by momentary distortions in the "electron clouds" of molecules. As a result, London dispersion forces tend to be more pronounced in larger molecules because larger molecules have larger electron clouds that are more polarizable.

The impact of intermolecular forces and branching on boiling point

Lower boiling compounds have shorter retention times than higher boiling compounds. For compounds with the same functional group and same number of carbons, branching (smaller surface area) decreases the boiling point.

Glycine and Polarized Light

Molecules with one or more stereocenters (chiral molecules) rotate plane polarized light. A stereocenter forms when one atom is bonded to four unique groups, and can be arranged in either of two ways. All of the standard amino acids are chiral except glycine

Muscle Fiber Potential

Muscle fiber action potentials propagate along the sarcolemma, the plasma membrane of the muscle fiber. The sarcolemma burrows deep into the muscle fiber, forming hollow structures known as transverse (T) tubules. Action potentials propagate along T-tubules just as they propagate along the superficial sarcolemma, resulting in the rapid and complete depolarization of the muscle fiber. This promotes calcium release from the sarcoplasmic reticulum, leading to muscle fiber contraction.

does CDNA contain introns?

NO!!Complementary DNA (cDNA) is derived from mature mRNA through reverse transcription. Because the mature mRNA has already been spliced (ie, introns were removed), the cDNA will not contain any introns. The cDNA can be cloned into expression vectors such as plasmids, which can be introduced into embryonic cells and integrated into the genome. These cloned genes can then be expressed in the organism. However, because the cloned gene does not contain any introns, its expression will not include splicing.

negative selection

Negative selection is the process by which immature T cells and B cells possessing receptors that bind to self-antigens are destroyed or inactivated. These cells are either eliminated by programmed cell death (ie, apoptosis) or made unresponsive to antigens (anergic). According to the question, rheumatoid factor (RF) is an antibody that mediates an autoimmune response by targeting a patient's own IgG antibodies. B cells and T cells that mediate recognition and destruction of self-antigens are typically destroyed during negative selection. This means that antibodies such as RF directed at self-antigens are not typically found in the human body.

Can acetyl CoA be used to make glucose?

No, once it is Acetyl-CoA, it must undergo OXPHOS Acetyl-CoA cannot provide additional carbon for glucose synthesis. Although acetyl-CoA can be converted to oxaloacetate through the citric acid cycle, it must first combine with an oxaloacetate molecule to do so, thereby consuming it; the two carbons gained by adding acetyl-CoA to oxaloacetate are effectively lost as CO2 during the cycle, so no net oxaloacetate is produced.

Nuclear localization sequences

Nuclear localization sequences signal for the transport of proteins such as transcription factors to the nucleus. According to the passage, SIRT4 colocalizes with the PDHC, which is found in the mitochondria.

The skin is divided into three main layers (ie, epidermis, dermis, and hypodermis). The epidermis can be further divided into five additional layers (strata) that contain Merkel cells, Langerhans cells, keratinocytes, and melanocytes. The deepest layer of the epidermis, or stratum basale, consists of a single row of stem cells that continually divide to give rise to new stem cells.

Of the two daughter cells produced from each mitotic division in the stratum basale, one cell remains in the basal layer (to continue proliferating) and the other begins differentiating into a mature keratinocyte. As constant cell division pushes the keratinocytes outward through the epidermal layers, they fill with keratin, flatten, and lose their organelles. The outermost layer of the epidermis, the stratum corneum, is composed of 20-30 layers of these dead keratin-filled cells and functions as a physical barrier to protect against pathogens, ultraviolet light, water loss, and injury.

What band does not change in length during muscle contraction

The A Band

Oogenesis

Oogenesis is the process by which females produce sex cells (gametes) called eggs. All of a woman's developing eggs (oocytes) are produced during fetal development. At birth, their maturation is arrested in prophase I; these arrested eggs are known as primary oocytes. At puberty, the menstrual cycle begins, and each month a single primary oocyte develops into a secondary oocyte by continuing meiosis up to metaphase II.

Oxidation of alchols

Oxidation of an organic molecule requires a decrease in the number of C-H bonds and an increase in the number of C-O bonds. Primary and secondary alcohols can be oxidized to form carboxylic acids and ketones, respectively, using various oxidizing agents such as chromic acid. However, the tertiary carbon of a tertiary alcohol does not have any C-H bonds to lose; therefore, its number of bonds to oxygen cannot be increased. If the number of bonds to oxygen were increased without losing a bond to hydrogen, the carbon atom would have five bonds exceeding the maximum number possible (four bonds

Oxygen Consumption in the Electron Transport Chain

Oxygen consumption in the electron transport chain takes place in complex IV, where O2 gets reduced to become water. The electrons needed to reduce oxygen are provided by reduced cytochrome C (cyt-Cred), which is converted to its oxidized form (cyt-Cox) in the reaction catalyzed by complex IV.

PTH and vitamin D

PTH release stimulates the synthesis of the active form of vitamin D (calcitriol) in the kidneys. Consequently, active vitamin D primarily functions to promote absorption of dietary calcium from the small intest

phospholipid structures

Phospholipids are a main component of the cell membrane and are responsible for the cell membrane's structure. They are amphiphilic molecules made of a hydrophobic (nonpolar) tail and a hydrophilic (polar) head group. This characteristic causes the phospholipid molecules to arrange into a bilayer in aqueous environments. The hydrophobic tails form the inner portion of the bilayer to keep away from water, and the hydrophilic heads encompass the outer portion of the bilayer toward water because the polar head group molecules can form favorable interactions with water, such as hydrogen bonds.

PCR

Polymerase chain reaction (PCR) uses thermal cycling to amplify small DNA fragments, which can then be screened for mutations or used in further genomic analysis. PCR reagents include the following: A source DNA template (containing deoxyribonucleotides) that includes the target region to be amplified and its adjacent flanking sequences where primers bind Primer pairs designed from the oligonucleotide sequence of the regions flanking the target sequence A thermostable DNA polymerase (ie, not denatured at high temperatures) to replicate the DNA template using a pool of supplied deoxyribonucleoside triphosphates (dNTPs) A buffer solution with positively charged ions (cations) to provide an optimal environment for DNA polymerase to function (ie, cations bind the negatively charged phosphates on the DNA backbone and those on dNTPs, neutralizing the negative charge of DNA and stabilizing primer-template binding)

polyubiquitin tags

Polyubiquitin tags target defective or unnecessary proteins for destruction by the proteasome. SIRT4 is used routinely in the cell, so it would have a polyubiquitin tag only if it were defective.

Proto-oncogenes

Proto-oncogenes are wild-type (WT) genes that are normally involved in cell cycle progression (eg, cell division stimulation, apoptosis prevention). However, when proto-oncogenes are mutated into oncogenes via activating mutations in one or two alleles, cells become cancerous. As a result, oncogenes lead to either an overexpressed protein, a hyperactive protein, or both, promoting uncontrolled cell proliferation.

Hydrogen Atom acidity

Protons on an α-carbon (adjacent to a carbonyl) are more acidic than other protons bonded to a carbon atom because the carbonyl oxygen is electron withdrawing, resulting in less electron density around the α-protons. Therefore, α-protons have lower pKa values and can be more easily removed by a base to form an enolate, which can be stabilized by charge delocalization.

Different types of neuroglia exist in the peripheral nervous system (PNS): what are they?

Schwann cells: form myelin sheaths around axons to increase speed of conduction. Satellite cells: provide structural support and supply nutrients to neurons..

Sebum

Sebum, an oily substance secreted onto the skin surface by sebaceous (oil) glands, also plays a minimal role in waterproofing the skin. A patient with full-thickness burns would be less able to retain fluids and electrolytes because the physical barrier that normally seals water inside the body (ie, the skin's outer layer) has been damaged or lost; therefore, this patient is at risk for extensive fluid loss.

Sacromers consists of several sections

Skeletal muscle is muscle that is attached to bone and functions in voluntary movement. In this type of muscle, each muscle fiber (ie, muscle cell) contains thousands of sarcomeres, or individual functional units. Sarcomeres are crucial to the process of muscle contraction. Sarcomeres consist of several sections: The I band consists of only actin (thin) filaments. The H band consists of only myosin (thick) filaments. The A band, which consists of both actin and myosin filaments, marks the length of the myosin filaments. The M line marks the center of each sarcomere. The Z line delineates the boundary between each sarcomere.

Solubility and Intermolecular Forces

Solubility depends on the ability of the solute and solvent molecules to interact through complementary, non-covalent intermolecular forces that form attractions between the molecules. Solute molecules that can associate with solvent molecules through similar types of intermolecular forces tend to be attracted to the solvent, and thus are more soluble in it.

Spermatogenesis

Spermatogenesis, a hormone-driven process in which male gametes (sperm) are produced, occurs in the seminiferous tubules of the testes (ie, the male gonads). The outer fibrous capsule of the testes encloses the seminiferous tubules, which are coiled and divided into numerous compartments. A cross-section of these tubules shows that they contain developing sperm cells and "nurse cells" known as Sertoli cells, which provide nourishment to sperm and regulate their development. In addition, the interstitial tissue of a seminiferous tubule houses Leydig cells, which secrete testosterone in response to the release of luteinizing hormone from the anterior pituitary and stimulate sperm cell differentiation. Spermatogonia are stem cells that undergo cell division to become mature sperm and appear near the basement membrane of the seminiferous tubule. Spermatogonia first divide by mitosis to yield two daughter cells: one remains as a spermatogonia stem cell to maintain the line and the other differentiates into a spermatocyte upon beginning meiosis I. Spermatocytes subsequently become spermatids upon completion of meiosis II. Spermatids then become spermatozoa (mature sperm) through the loss of most of their cytoplasm, acrosome formation around the nucleus, mitochondrial concentration around the midpiece, and development of a tail (flagellum). At this point, the spermatozoa that result are small, nonmotile gametes that bear little resemblance to the original spermatogonia. As sperm develop, they are transferred from the basement membrane and released into the lumen of the seminiferous tubules. Following this, sperm exit the testes and are carried to the epididymis, where they become motile and are store

Sphingolipids

Sphingolipids are structural lipids that help influence the fluidity and curvature of biological membranes. The long hydrocarbon chain of the sphingosine head group cannot be readily hydrolyzed, and sphingolipids are not a primary means of energy storage.

Succinate ubiquinone reductase

Succinate-ubiquinone reductase, also known as Complex II or succinate dehydrogenase, is an oxidoreductase found in the inner membrane of the mitochondria in eukaryotes. In the electron transport chain, Complex II facilitates the transport of electrons from succinate (in the citric acid cycle) to Complex III. Electrons move through Complex II by three consecutive reactions. First, electrons from succinate are transferred to flavin adenine dinucleotide (FAD) to produce FADH2 as succinate is oxidized to fumarate. FADH2 is then reoxidized to FAD when electrons are shuttled to the iron-sulfur centers in Complex II. Finally, a small mobile electron carrier called ubiquinone, or coenzyme Q, accepts electrons from the iron-sulfur centers, becoming reduced to ubiquinol. Ubiquinol then transports its electrons to Complex III.

Enzyme activity may be modulated by formation of covalent bonds between amino acid residues and various chemical groups, such as phosphates (phosphorylation) or sugars (glycosylation). These modifications may increase or decrease the activity of the enzyme, depending on the enzyme itself and the site of the modification.

Take away, these are covalent modifications!

The Krebs cycle is allosterically regulated by

The Krebs cycle is allosterically regulated at the irreversible steps catalyzed by citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase. The Krebs cycle enzymes are inhibited by NADH, ATP, citrate, and succinyl-CoA, and are activated by ADP and calci

The Michaelis-Menten equation relies on three assumptions:

The Michaelis-Menten equation relies on three assumptions: The free ligand approximation states that substrate concentration [S] is constant during the reaction. This approximation is only true during the initial phase of the reaction, before a significant amount of substrate is converted to product. Substrate can also be depleted when it binds the enzyme to form the enzyme-substrate complex (ES). To ensure that ES formation does not significantly impact [S], the total concentration of enzyme in solution should be much smaller than any substrate concentration tested (Number III). The steady state assumption states that the concentration of ES remains constant over the course of the reaction, allowing the rate of product formation to remain constant. Once [S] becomes significantly depleted, ES levels decrease and the reaction slows. The irreversibility assumption states that the reaction proceeds only in the forward direction, and product does not get converted back to substrate. Once enough product accumulates, the reverse reaction occurs at non-negligible levels and further slows the net rate of product formation.

Formation of Alanine through Strecker Synthesis

The Strecker synthesis is used to make α-amino acids from an aldehyde using ammonium chloride (NH4Cl) and potassium cyanide (KCN). The first step of the reaction proceeds with protonation of the carbonyl oxygen by ammonium (NH4+), followed by nucleophilic attack of the carbonyl carbon by ammonia (NH3), resulting in dehydration and imine formation. In the second step, a cyanide anion is added to the imine to form an aminonitrile. Finally, in the third step, the nitrile (R-CN) nitrogen is protonated, and two water molecules add to the nitrile carbon in succession, eliminating ammonia from the nitrile and forming the carboxylic acid of the α-amino acid.

Why are alkali metals so reactive?

The alkali metals are very reactive because of their low ionization energy, large atomic radius, and small electronegativity. Cesium is considered the most reactive metal

lytic cycle

The general steps involved during the lytic life cycle are described as follows: Attachment: The bacteriophage contacts the bacterial cell wall and attaches to the host bacterium using its tail fibers. Viral genome entry: The phage uses its tail sheath to inject its genome into the cytoplasm of the bacterial host (Number I). Host genome degradation: Viral enzymes degrade the host genome into its nucleotide components to provide the building blocks for replication of the viral genome (Number III). Synthesis: Loss of the bacterial (ie, host) chromosome ends the synthesis of host molecules, now under the control of the viral genome. As a result, the host machinery (eg, ribosomes) begins to synthesize the components needed for new viral progeny, which then assemble inside the host cell. Release: Many newly assembled viral progeny (virions) are released as the bacterium disintegrates (lysis) due to the action of lysozymes on the host cell wall.

What are the sex hormones?

The hormones testosterone, estrogen, and progesterone are referred to as sex hormones because of their role in sexual development and reproduction. Although testosterone can be detected in the serum of females, it is typically considered a male sex hormone because of its role in the development of male traits and behaviors.

neuromuscular junction

The interface between a somatic motor neuron and a skeletal muscle fiber is a specialized synapse known as the neuromuscular junction (NMJ). The basic function of the NMJ is to convert a motor neuron action potential into a muscle fiber action potential. Activity at the NMJ begins on the presynaptic side. The arrival of an action potential at the axon terminal of the presynaptic motor neuron triggers a series of processes that result in the release of ACh from presynaptic vesicles and into the synaptic cleft via exocytosis. ACh diffuses across the synaptic cleft to bind nicotinic ACh receptors (nAChRs) embedded within the membrane of the postsynaptic muscle fiber, eventually leading to muscle contraction. Unbound ACh may diffuse away from the synapse or be degraded by the enzyme acetylcholinesterase (AChE), terminating muscle fiber contraction.

Charge Length and Magnitude can be separated by Resonance

The magnitude of the dipole momentμ of a polar bond is equal to the product of the magnitude of the partial charge q and the charge separation distance r (ie, the chemical bond length): μ = qr In general, atoms with a greater difference in electronegativity have more separated charge and form stronger dipoles than other bonds of comparable length. Relative bond lengths (taken as the sum of the atomic radii) can often be assessed qualitatively based on periodic trends in the atomic radii of the atoms and on the bond order (ie, higher bond order indicates a shorter bond). The higher bond order rightly predicts that the C=O bond is shorter than the C-O bond. The electronegativity difference between the atoms is the same in both bonds, and this suggests the same amount of separated charge across both bonds; however, the electronegativity difference does not account for the effects of resonance in the C=O bond. The π bond in C=O is capable of momentary delocalization to the O atom via resonance.

Enzyyme Saturation

The maximum possible reaction rate Vmax of an enzymatic reaction is limited by the number of enzyme active sitespresent in solution. A Michaelis-Menten graph depicts the rate of an enzymatic reaction V0 as a function of substrate concentration [S] when the concentration of enzyme [E] is fixed. As [S] increases, the number of active sites bound by substrate also increases, leading to a faster reaction rate. When [S] is sufficiently high, all enzyme active sites are bound (saturating conditions) and Vmax is achieved. In contrast, when [S] is not saturating, some enzyme active sites are not bound by substrate and the reaction proceeds at a rate that is slower than Vmax. Accordingly, only when the enzyme is operating at Vmax does substrate occupy every active site in solution.

Division of the nervous system

The motor nerve fibers of the somatic nervous system transmit impulses from the central nervous system to the skeletal muscles of the body, allowing individuals to consciously control and perform specific movements. As a result, all movements carried out on a voluntary basis are mediated by the somatic nervous system. Examples of voluntary movements include activities such as walking, talking, and movement of the jaw during chewing. In contrast, the autonomic nervous system mediates subconscious, automatic functions that are not subject to voluntary control. Accordingly, the activity of glands, smooth muscles, and cardiac muscles is regulated by the visceral motor nerve fibers of the autonomic nervous system. For example, the smooth muscle sheets in the walls of the gastrointestinal tract alternately contract and relax to propel food contents along the gut (peristalsis) (Choice C), and the smooth muscles located within the walls of blood vessels can constrict or dilate the vessel to regulate blood pressure (Choice A). The contraction of cardiac muscle is another automatic, involuntary process regulated in part by the autonomic nervous system (Choice B). Although the action potentials necessary for cardiac contraction are generated by cardiac tissue independent of nervous system input, the activity of autonomic nerves influences the frequency and intensity of cardiac contraction.

oogensis

The ovaries are female reproductive structures that produce gametes and secrete sex hormones. Oogenesis or female gamete (ovum) production occurs in the ovaries as follows: In utero, oogonia (ovarian stem cells) of the female embryo rapidly multiply via mitosis to generate primary oocytes, which are surrounded by specialized cells that form a saclike structure known as a follicle. Female gametes must undergo meiosis to mature. Primary oocytes begin the first meiotic division but become arrested at prophase I until puberty. At puberty, hormonal changes during each menstrual cycle result in a single follicle being selected to continue meiosis I. Completion of meiosis I produces one haploid secondary oocyte and one small polar body that ultimately degenerates. The secondary oocyte begins the second meiotic division but is arrested at metaphase II. In the ovulation phase of the menstrual cycle, the follicle ruptures and the secondary oocyte is released into the abdominal cavity. The secondary oocyte enters the fallopian tubes, where it can be fertilized by a sperm cell. If fertilization occurs, the secondary oocyte will complete meiosis II to form one large ovum (fully mature) and a second polar body that degenerates.

If pH < pKa, then [HA] > [A−]; if pH > pKa, then [HA] < [A−].

The pKa is a measure of the acidity of a particular proton in a molecule. when the pKa is equal to the pH in a buffer system, the amount of unprotonated acid (HA) is equal to the amount of deprotonated conjugate base (A−), and [HA] = [A−]. If pH < pKa, then [HA] > [A−]; if pH > pKa, then [HA] < [A−].

parathyroid hormone

The parathyroid glands secrete parathyroid hormone (PTH), which functions to regulate serum Ca2+ levels. The parathyroid gland does not directly regulate the synthesis and secretion of glucocorticoids.

second ionization energy

The second ionization energy is the energy required to remove the second of two electrons from an atom. The second ionization energy tends to increase across a period and to decrease down a group; however, ionizations involving core electrons are higher energy than those involving valence electrons. General Chemistry Subject Atoms & Molecules Foundation Scientific Reasoning and Problem-solving Skill

bond length and acidity

The size of the halogen atom impacts the bond length and strength of hydrogen halide acids (H−X). Halogens are located in Group 7A (Group 17) on the right side of the periodic table and increase in size moving down the group. Therefore, halogens with a smaller atomic number have a smaller atomic radius and form shorter, stronger H−X bonds that are more difficult to ionize. Smaller halogens are more electronegative and more readily attract electrons in the H−X bond toward itself, creating a polar covalent bond.

Bromination

The α-carbon of a carboxylic acid is the carbon atom adjacent to the carbonyl carbon, and it is susceptible to substitution reactions such as bromination. The carbonyl carbon of a carboxylic acid may be temporarily brominated, but this carbon is susceptible to hydrolysis when water is added.

An object is launched with a one-time burst of propulsion away from the surface of the Moon. After the burst, which of the following best describes the changes that occur as the object moves away from the Moon's surface? A. The object mass is dissipated as heat. (0%) B. Potential energy is converted into kinetic energy. (38%) C. Kinetic energy is converted into potential energy. (55%) D. Total mechanical energy is not conserved. (4%)

The work-energy principle states that the total work W done by a force is equal to the change in kinetic energy (ΔKE) of the object acted upon by the force: W=ΔKEW=ΔKE If the forces acting on the object are conservative forces (eg, gravity), then the work done by the force also contributes to a change in the potential energy of the system (ΔPE): W=−ΔPEW=-ΔPE Combining these two equations yields a statement expressing the conservation of energy in mechanical systems: ΔKE=−ΔPEΔKE=-ΔPE ΔKE+ΔPE=0ΔKE+ΔPE=0 Furthermore, the above equation may be restated in terms of the initial (i) and final values (f) of each variable: (KEf−KEi)+(PEf−PEi)=0KEf-KEi+PEf-PEi=0 KEi+PEi=KEf+PEfKEi+PEi=KEf+PEf Consequently, within purely mechanical systems any change in the kinetic energy is accompanied by an equal and opposite change in potential energy such that total mechanical energy remains the same in both conditions. After the object (eg, a rocket) is launched from the Moon, the only force present in the system is gravity. As the rocket moves away, the gravitational force is oriented toward the Moon. Therefore, work done by gravity progressively decreases the velocity and the kinetic energy of the object: KEi>KEfKEi>KEf Simultaneously, the potential energy of the object increases (becomes less negative) as the radial distance from the mass increases: PEi<PEfPEi<PEf The decrease in the kinetic energy of the object is accompanied by an increase in the potential energy of the object such that conservation of energy is maintained.

Similarities between mitosis and meiosis

There are some similarities between meiosis and mitosis: DNA synthesis occurs prior to cell division (ie, during the S phase of interphase). In a given organism, parent cells have the same chromosome number (eg, diploid or 2n in humans). Both are divided into the same general stages (ie, prophase, metaphase, anaphase, telophase). One parent cell divides to produce multiple daughter cells.

Thin-layer chromatography (TLC

Thin-layer chromatography (TLC) is a technique used to separate compounds based on polarity. The mobile phase travels up the stationary phase via capillary action. In normal-phase TLC, the stationary phase is made of a polar adsorbent material, typically silica (SiO2), and the mobile phase is a nonpolar organic solvent. The components of a mixture in the solvent travel up the plate at different rates based on their polarity. Nonpolar compounds have less affinity for the polar stationary phase than polar compounds, so they interact with the stationary phase less and travel farther up the plate. The Rf value is expressed by the ratio of the distance traveled by the compound of interest to the distance traveled by the mobile phase (solvent front). The Rf value is always less than 1 and when two compounds are compared, a larger Rf value corresponds to the less polar, more mobile compound.

Watson-Crick base pairing Hydrogen Donors vs Hydrogen Acceptors

Thymine, Uracil and Adenine: One donor and one acceptors Guanine: 2 donors, 1 acceptors Cytosine: 1 donor, 2 acceptors

precipitating dna with ethanol explain

To precipitate the DNA from aqueous solution, its charge must be neutralized through extraction with ethanol and a salt such as sodium acetate. Mixing the aqueous layer with ethanol disrupts the hydration shell around DNA molecules, allowing for sodium cations to better interact with the negatively charged DNA backbone. Sodium cations then neutralize DNA's charge via ionic bonding with phosphate groups, making DNA less hydrophilic, decreasing its affinity for the aqueous solvent, and allowing it to precipitate more efficiently.

tumor suppressor genes

Tumor suppressor genes (or antioncogenes) regulate DNA repair by repressing or pausing the cell cycle to ensure that only normal cells proceed to the division (mitosis) stage. These genes also prevent accumulation of mutations in cancer cells by either repairing the mutations or inducing programmed cell death (apoptosis) if repair fails. In the setting of cancer, tumor suppressor genes become inactivated by loss of function mutations in both alleles and lose the ability to prevent abnormal growth and division of damaged cells.

Enveloped vs. non-enveloped viruses

Viruses possess DNA or RNA genomes surrounded by a protein capsid and are unable to reproduce outside of a host. Viruses can also be classified as either enveloped (have a phospholipid bilayer as the cell membrane) or nonenveloped (no phospholipid bilayer). In contrast, all prokaryotic and eukaryotic cells are enclosed by a phospholipid bilayer.

nucleophilicity and electronegatvity

When comparing the nucleophilicity of atoms of equal negative charge, nucleophilicity tends to increase from right to left across a row of the periodic table as electronegativity decreases. Atoms of higher electronegativity more effectively stabilize negative charge and less readily donate electron density to electrophiles whereas those of lower electronegativity stabilize a negative charge less effectively and more readily donate electrons to electrophiles.

When homologous chromosomes fail to align properly, _________ _______ _______ occurs.

When homologous chromosomes fail to align properly, unequal crossing over occurs. Unequal crossing over is the exchange of unequal segments of DNA between non-sister chromatids, yielding one chromosome that contains extra copies of one or more genes (ie, gene duplication) and another chromosome that lacks those genes entirely (ie, gene deletion).

cDNA

When scientists are interested in specific mRNA transcripts (ie, expressed genes), reverse transcriptase polymerase chain reaction (RT-PCR) can be used to analyze cells. Reverse transcriptase (an enzyme) is used to convert mRNA to double-stranded cDNA, which can then be amplified through PCR using primers specific to the mRNA transcript of interest. Afterward, samples can be analyzed using gel electrophoresis for the presence or absence of a specific transcript.

MicroRNAs(miRNAs)

are small, noncoding eukaryotic or viral RNA molecules that bind complementary sequences on target messenger RNA (mRNA) molecules, consequently inhibiting their expression. miRNAs, such as those encoded by the miR-17~92 gene cluster described in the passage, act to silence gene expression at the translational level. Following binding, miRNA-mediated silencing occurs either by promoting endonuclease activation and subsequent cleavage of the target mRNA or by preventing the target mRNA from binding to ribosomes (blocking translation). As a result, the miR-17~92 gene cluster products are miRNAs that interfere with the expression of specific genes by binding target transcripts containing complementary nucleotide sequences.

However, fully developed sperm generally have little to nonexistent ____

cytoplasm A human sperm cell is divided into three segments: a head, a midpiece, and a tail (flagellum). The head contains an acrosome and the nucleus. The acrosome is a flattened structure that encapsulates the tip of the nucleus and is rich in specialized lysosome-like enzymes for piercing the outer shell of an oocyte during fertilization. The midpiece section is packed with mitochondria, essential organelles that produce the ATP required for flagellum-driven sperm motility. This section also contains a pair of central microtubules that are anchored to the cytoskeleton and extend down the length of the flagellum (tail region). The tail, or flagellum, is a singular elongated structure specialized for wavelike movements to propel sperm through a fluid environment. Flagellum-driven motility is derived from the action of ATP-dependent motor proteins that act on the central microtubules.

The molecular weight of dNMPs in decreasing order is

deoxyguanosine (dGMP), deoxyadenosine (dAMP), deoxythymidine (dTMP), and deoxycytidine (dCMP).

Electron affinity is the quantitive measure of the

energy change when the electron is added to an atom in the gas state. The more negative the change in energy, the more energy released upond addition of an electron. Although EA generally increases (becomes more negative) from left to right across a period, EA generally decreases (becomes more positive) going down a group because the electron is added at an increased distance from the nucleus. The exception to this trend is when an atom is very small (ie, first or second period). Small atoms such as oxygen and fluorine have several electrons crowded around a small nucleus, resulting in greater electron-electron repulsion. Adding another electron would increase repulsion forces even further. Therefore, it is more difficult to add an electron to oxygen than to a larger atom with lower repulsion forces.

fatty acid contains how many carbons?

fatty acid contains 2n + 2 carbons.

How to calculate change in amino acid substitution

final - initial charge for amino acid

Fisher Esterification

formation of ester from carboxylic acid and an alcohol initiated by an acid catalyst acid catalyst protonates the alcohol --> forms oxonium ion --> protonates carboxylic acid --> carboxylic acid open to nucleophilic attack by the alcohol --> water eliminated yields protonated ester

action potential and SA nodes

heart rate is tightly regulated by the SA and AV nodes, specialized clusters of self-depolarizing cells found in the upper atrial wall and lower interatrial septum, respectively. Normally, depolarization occurs via the influx of positive ions (ie, Na+, Ca2+) into SA and AV nodal cells, increasing cell membrane potentials and generating APs. APs fired from the SA node travel through cardiac muscle cells of the atria, inducing atrial contraction and ventricular filling. At the AV node, relay of APs to ventricular cells is delayed, ensuring that ventricular filling is complete prior to ventricular contraction. Next, APs travel through both ventricles, causing them to contract and expel blood into the arteries. The electrical activity of the heart is often measured using an ECG machine, a device that records APs generated by SA and AV nodal cells as well as cardiac muscle cells. In this scenario, the physician orders an ECG to measure the electrical activity of the patient's heart. Compared to a healthy individual's ECG, the patient's ECG shows more waves of atrial and ventricular depolarization over the same time period.

If a protien is "more degradable", how will this show up in an SDS page gel for instance

it would not be as intense Proteases degrade proteins into fragments by hydrolyzing the peptide bonds that link amino acids in the polypeptide chain. For SDS-PAGE of a degradable protein, treatment with increasing protease concentrations is correlated with decreased band intensity (abundance) of protease-resistant fragments per lane.

Amino acids (except for --------) can be converted into glucose through gluconeogenesis. For example, alanine can be converted to pyruvate by deamination, and pyruvate can then enter gluconeogenesis.

leucine and lysine

The number of mutations increases _____ with time

linearly According to the neutral theory of molecular evolution, most genetic mutations are neutral and do not affect the fitness (reproductive success) of an organism. Genetic drift leads to the random fixation or loss of neutral mutations; ultimately, however, these neutral mutations accumulate at a fairly constant rate in a species over evolutionary time. This accumulation of neutral mutations in the homologous DNA of species is said to be linear and is referred to as a "molecular clock." The molecular clock model allows researchers to measure evolutionary time and estimate the evolutionary relationships between species by analyzing the rate of neutral mutations in the genome.

Antibodies bind their epitopes throug _______ such as hydrogen bonding and electrostatic attractions.

noncovalent interactions

non disjuction occurs during what for meiosis

nondisjunction can occur during anaphase of either meiosis I or meiosis II, and results from the failure of one or more pairs of either homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate. Although homologous chromosomes have already segregated during anaphase I, nondisjunction of sister chromatids can still occur during anaphase II after fertilization.

ACeteone, Methanol and Water are all ____ solvents

polar

Protozoa

protozoa (eg, Plasmodium falciparum) are single-celled eukaryotic organisms, they would possess all the unique characteristics of eukaryotic cells, including a spliceosome-mediated mechanism for splicing introns from mRNA in the nucleus.

first order

rate is directly proportional to concentration

Telomees

ue to a phenomenon called the end-replication problem, the ends of a chromosome cannot be completely replicated, so a chromosome shortens slightly after each replication event. This shortening occurs at the ends of the chromosome, called the telomeres. Telomeres are noncoding DNA sequences that protect the rest of the chromosome from degradation by being slowly degraded themselves. If telomeres encoded proteins, some of the coding information would be lost each time the cell replicated, which would be harmful to the cell. For this reason, telomeres do not encode any proteins When telomerase extends telomeres, it does so by adding the sequence 5′-TTAGGG-3′ to the end of one of the strands on the chromosome multiple times in succession. DNA polymerase then adds the complementary bases to the other strand to generate double-stranded DNA. As a result, telomeres contain highly repetitive DNA, with the repeated sequence being 5′-TTAGGG-3′.

constant velocity =

zero acceleration i.e a golf ball only accelerates when a nonzero net force is exerted upon it

Transport and Activation of Fatty Acids in the Mitochondria

β-oxidation is the breakdown of fatty acid chains into acetyl-CoA through a series of oxidation reactions in the mitochondrial matrix that produce NADH and FADH2, which can be used to synthesize ATP. Short- and medium-chain fatty acids can diffuse through the inner and outer membranes of the mitochondria, but long-chain fatty acids obtained from lipid stores must undergo a set of reactions to enter the mitochondrial matrix. First, fatty acids in the cytoplasm are activated when the enzyme acyl-CoA synthetase attaches them to the carrier molecule CoA using ATP. Subsequently, in the rate-limiting step of the reaction, carnitine palmitoyltransferase I(CPTI) converts fatty acyl-CoA molecules to fatty acylcarnitine, which enters the intermembrane space. Fatty acylcarnitine is then moved by acylcarnitine translocase across the inner membrane and into the matrix. Lastly, to begin the oxidation reactions, carnitine palmitoyltransferase II (CPTII) on the inner membrane reconverts fatty acylcarnitine to fatty acyl-CoA, which can be broken down into acetyl-CoA. Therefore, if the researchers wanted to confirm that fatty acid oxidation was not impaired, they would need to ensure that translocation of acylcarnitine into the mitochondrial matrix was functional.

Nondisjunction

)Nondisjunction is defined as the failure of homologous chromosomes to separate in anaphase of meiosis I or the failure of sister chromatids to separate in anaphase of meiosis II. Consequently, nondisjunction produces gametes that either lack a copy of a chromosome or contain an extra copy of a chromosome.

Gabriel Synthesis

- An amino acid is generated from phthalimide (nucleophile) and diethyl bromomalonate, using two SN2 reactions, hydrolysis, and decarboxylation.

Parallel vs antiparallel beta sheets

-antiparallel beta sheets are slightly stronger due to the optimal hydrogen bonding pattern -parallel = all go same way -antiparallel = alternate which way Beta-sheets can be oriented in either a parallel or an antiparallel manner. The passage states that the sheets in ataxin-3 are in the parallel orientation. Parallel strands run in the same direction, so the N-terminal portion of one strand aligns with the N-terminal portions of the others. On the other hand, in antiparallel sheets the individual strands run in directions opposite to each other, so the N-terminal portion of one strand lines up with the C-terminal portion of neighboring strands. Because antiparallel strands run in opposite directions, they may be linked by a short sequence of amino acids called a beta-turn that induces a 180° bend in the polypeptide chain. Parallel beta-strands do not reverse directionality, so neighboring strands must instead be linked by longer loops that make 360° turns to align the N-terminal regions of neighboring strands.

the buggering range is ____ ph units away from the buggers pKa

1 pH unit away

a buffer with a pka of 6 has a Ka of

10^-6

Prion

A prion is a misfolded protein that acts as an infectious agent by inducing changes in the secondary structures of other normal proteins, causing these normal proteins to also become misfolded. These misfolded proteins are less soluble, so they aggregate and can cause disease. Because they are proteins, prions do not contain genetic material (ie, DNA, RNA).

blood clot formation steps

A single layer of endothelial cells comprises the inner wall of all blood vessels, forming a barrier that regulates the entry and exit of materials into and out of the bloodstream. In addition, endothelial cells secrete chemical signals that generally prevent blood coagulation (ie, clotting). However, injury to a blood vessel that results in bleeding indicates damage to the endothelium and triggers the following cascade of events: Formation of the platelet plug. Endothelial damage exposes connective tissue (ie, collagen fibers) normally present outside the blood vessel. Circulating cell fragments called platelets (derived from the bone marrow) readily bind these collagen fibers, aggregating to form a platelet plug (clot) that prevents blood flow out of the vessel. In addition, bound platelets and endothelial cells near the site of damage continue to release signals that enhance platelet aggregation. Strengthening of the clot. Clotting factors (mainly synthesized in the liver) are specialized proteins that become activated in response to platelet aggregation and signaling factors outside the vessel. Activated clotting factors induce processes that lead to the formation of the enzyme thrombin. Thrombin induces protein strands (ie, fibrin) to form an adhesive mesh-like structure over the platelet plug, reinforcing the clot.

Torque

A torque (τ) is a rotational force caused by a translational force (F) applied at some radial distance (r) from a center of rotation. Torques can cause rotation about a central axis or oppose any rotation already present. The magnitude of a torque is defined as: τ=rF sin θ where θ is the angle between the translational force and the radial vectors. When r and F are perpendicular (θ = 90°), the torque is maximal: τ=r⋅F sin90° τ=r⋅F Conversely, when r and F are parallel (θ = 0°), the magnitude of torque is zero (the force has no rotational influence).

fat soluable vitamins are

A, D, E, K

When acetylcholine (ACh) is released by the motor neuron at the neuromuscular junction, the following occur:

ACh binds and opens ligand-gated ion channels in the sarcolemma (the plasma membrane of the muscle cell) Na+ flows down its electrochemical gradient and into the cell through the channel, resulting in depolarization of the sarcolemma and generation of an action potential that propagates along the muscle fiber in all directions. At certain locations along the muscle fiber, the sarcolemma burrows deep into the cells, forming a channel known as the transverse (T) tubule, which brings depolarizing current close to the sarcoplasmic reticulum (SR) The SR is a specialized smooth endoplasmic reticulum responsible for regulating cytosolic Ca2+ levels within the muscle cell. Action potential propagation through the T tubule ultimately leads to the opening of Ca2+ channels in the SR membrane. Because Ca2+ is more highly concentrated inside the SR than in the cytosol, the opening of these channels results in Ca2+ flowing down its concentration gradient and into the cytosol. Cytosolic Ca2+ ions then bind to troponin, which allows the actin and myosin filaments of the sarcomere to slide across one another. The sliding of the filaments results in shortening of the sarcomere and overall muscle contraction The Ca2+ channels in the SR membrane close when the depolarizing stimulus ceases. Active transport Ca2+ pumps sequester the Ca2+ back into the SR, which allows the muscle to return to its relaxed state as cytosolic Ca2+ concentration falls

neuromuscular junction

Acetylcholine (ACh), a neurotransmitter, plays an important role in the sympathetic and parasympathetic (autonomic) nervous systems. In addition, ACh is the main neurotransmitter released by neurons of the efferent somatic nervous system, the system associated with skeletal muscle function. Contraction of skeletal muscles is stimulated by transmission of a nerve impulse at the neuromuscular junction, the synapse between a skeletal muscle and a motor neuron. When an action potential reaches the terminal of a motor neuron, an influx of calcium through voltage-gated calcium channels triggers the release of ACh-containing vesicles (exocytosis) into the synaptic cleft. Released ACh binds to receptors of the motor end plates, depolarizing the innervated muscle fibers and causing muscle contraction. Consequently, disruption of the release of ACh inhibits muscle contractions and causes skeletal muscle paralysis.

urination

After being formed in the nephron, urine is funneled into the ureters (the tubes connecting the kidneys to the bladder) for delivery to the bladder. Urine accumulates in the bladder until it exits the body via the urethra in a process called urination. Urination is controlled by musculature (both smooth and striated) lining the urinary tract. During urine collection, the detrusor muscle (the layer of smooth muscle lining the bladder) is relaxed. At the same time, the internal urethral sphincter (IUS, a ring of smooth muscle surrounding the urethra) and the external urethral sphincter (EUS, a ring of striated muscle downstream of the IUS) are contracted to prevent urine flow down the urethra. The detrusor and IUS are under involuntary control; the EUS is under voluntary control. During urination, activity within stretch receptors in the bladder leads to: Contraction of the detrusor muscle, which pushes urine out of the bladder and into the urethra Relaxation of the IUS, which opens the urethra and allows urine to pass

Preparation of a Tosylate

Alcohols are weak electrophiles and poor leaving groups; therefore, a nucleophile is unlikely to displace the hydroxyl group (-OH) of an alcohol. To improve its leaving group ability, an alcohol can be converted into a tosylate (-SO3C6H4CH3) or a mesylate (-SO3CH3). Tosylates are produced by the reaction of an alcohol with p-toluenesulfonyl chloride (TsCl) and a base, such as pyridine. The hydroxyl O acts as the nucleophile to attack the S of TsCl, and Cl acts as the leaving group. Then pyridine deprotonates the O atom, giving the tosylate product.

Why does ionization energy decrease down a group?

Alkali metals occupy Group 1 and have the lowest first ionization energies of all the element groups. As the atoms in the alkali metal group increase in size moving down the column, the valence electron occupies an increasingly higher level that is farther from the nucleus (ie, experiences less attraction) and is less tightly bound. As a result, less ionization energy is required to remove the electron from the valence shell of larger alkali metals, which makes them more reactive. Lithium is the smallest atom in Group 1 and has a valence electron in a lower levelwith a greater attraction to the nucleus (ie, the electron takes more energy to remove). Therefore, lithium is the least reactive of the alkali metals in Reactions 1-3.

nonionizable side chains have 2 pkas

All amino acids have ionizable carboxyl and amino groups with pKa values near 2 and 9.5, respectively. Therefore, all amino acid titration curves have two buffering regions, one near each pKa. Seven of the standard amino acids (R, K, Y, C, H, E, and D) also have ionizable side chains, each with a unique pKa. The titration curve for each of these amino acids has a third buffering region associated with the side chain pKa. Because the titration curve in the question shows only two buffering regions, the amino acid has only two pKa values. Therefore, its side chain is not ionizable and cannot exchange protons with water.

gluconeogenic and ketogenic amino acids

Amino acids are classified as glucogenic or ketogenic depending on the metabolic intermediates to which they are converted. Glucogenic amino acids are converted to pyruvate or citric acid cycle intermediates, which can then be converted to glucose. Ketogenic amino acids are converted directly to acetyl-CoA, which can enter the citric acid cycle or be used to form ketone bodies. The passage uses this classification to place amino acids into the three categories in Table 1. Amino acids in Category I are converted exclusively to pyruvate, and those in Category II become acetyl-CoA. Category III consists of amino acids used to make various citric acid cycle intermediates. Glycine and cysteine are Category I amino acids, which are converted directly to pyruvate. Patients with ME at rest have sufficient ATP to convert pyruvate to citric acid cycle intermediates (via oxaloacetate) during aerobic respiration. However, the shortage of oxygen caused by prolonged physical exertion inhibits aerobic respiration by preventing NAD+and FAD, which are used by the citric acid cycle, from being regenerated. To maintain ATP production during extended and intense exercise, muscle cells switch from aerobic to anaerobic respiration, which does not require oxygen and consists of glycolysis and fermentation. Glycolysis contributes two molecules of ATP for each glucose molecule converted to pyruvate. During fermentation, the NAD+ required for glycolysis to continue is generated by reducing pyruvate to lactate using the enzyme lactate dehydrogenase. Therefore, glycine and cysteine are ultimately converted to lactate during extended, intense periods of physical exertion.

Synaptic Transmission of Inhibitory Neurotransmitters

An AP is initiated in the post-synaptic neuron only if the membrane potential becomes more positive and exceeds a certain threshold (−55 mV). Depending on the neurotransmitter's effect on the post-synaptic neuron, synapses can be classified as excitatory or inhibitory. At an excitatory synapse, the pre-synaptic neuron releases neurotransmitters that cause an influx of positively charged ions (Na+) into the post-synaptic neuron. These ions cause the resting membrane potential of the post-synaptic neuron to become more positive, or to depolarize, which promotes AP initiation. In contrast, inhibitory synapses release neurotransmitters that affect the post-synaptic neuron by causing either an influx of negative ions (Cl−) or an efflux of positive ions (K+). The exit of positive ions or entry of negative ions into the post-synaptic neuron causes the cell's membrane potential to become more negative, or to hyperpolarize, which inhibits AP initiation.

Action Potential Steps

An action potential (AP) is a rapid electrical impulse that travels from the neuron's cell body to its axon terminal. It consists of a series of membrane potential changes, as follows: Resting membrane potential (RMP): The membrane potential of the resting neuron is −70 mV (ie, the inside of the neuron is 70 mV more negative than the extracellular space). RMP is maintained by the Na+/K+ pump and K+ "leak" channels, which always allow passive diffusion of K+ ions across the membrane. Ion channels that open or close based on changes in membrane potential (voltage-gated channels) are closed at RMP. Threshold: An excitatory stimulus causes several nearby voltage-gated Na+ channels to open, allowing Na+ ions to rush into the cell. Consequently, the membrane potential becomes more positive than the RMP (ie, depolarized). If the neuron depolarizes to its specific threshold value, an AP is fired. If the threshold is not reached, no AP is fired and the RMP is restored. Rising phase: At threshold, the remaining voltage-gated Na+ channels open, resulting in rapid depolarization of the local membrane. This rise in membrane potential triggers a positive feedback loop, opening more Na+ channels in adjacent segments to propagate the AP down the axon. Overshoot: The ongoing flood of Na+ into the cell causes the AP to reach its peak (overshoot), where the membrane potential is most positive. Falling phase: Voltage-gated Na+ channels close, and voltage-gated K+ channels open fully. K+ then rushes out of the cell, causing membrane repolarization and restoring RMP. Undershoot: Excessive K+ efflux causes the membrane potential to fall below the RMP (hyperpolarize), and the local membrane enters a refractory period (absolute or relative). RMP restoration: Both voltage-gated Na+ and K+ channels are inactive. The membrane potential returns to −70 mV and is maintained by the Na+/K+ pump until another action potential is initiated.

Two of the assumptions made by the ideal gas law are that the volume of the individual gas particles is negligible and the individual gas particles do not interact with each other. These assumptions are adequate for most gases at low pressure. However, at higher pressures the individual particles are closer together, resulting in an increased gas density.

An increased density results in a greater likelihood that the gas particles will interact with each other in an inelastic way. Furthermore, at extremely high pressures, the combined molecular volume occupied by the gas particles becomes significant relative to the volume of the container. These factors lead to deviations from ideal behavior in real gases.

Osteocyte Signaling

Bone is made of several types of cells surrounded by a firm matrix. Osteoprogenitor cells are stem cells that differentiate into another type of bone cell, the osteoblast. Osteoblasts participate in bone remodeling by secreting proteins that create the osteoid, or unmineralized bone matrix. In addition, osteoblasts promote the absorption of calcium and phosphate from the bloodstream and the incorporation of these molecules into the bone matrix. By building this matrix around themselves, osteoblasts eventually become surrounded and differentiate into osteocytes. Osteoclasts are large cells that participate in bone remodeling by breaking down (resorbing) old bone. Osteocytes are mature and mitotically inactive bone cells that maintain bone structure. These cells release signals to other bone cells to regulate compact bone remodeling. Because osteocytes are surrounded by bone matrix and are located within spaces called lacunae in the Haversian system, they cannot travel to other cells during signaling. Rather, they release signaling molecules responsible for stimulating other bone cells into canaliculi, the small canals that connect cells within the bone matrix. Signaling molecules released by osteocytes travel through these small canaliculi until they reach their target cells (ie, other bone cells).

Germ cell derivatives

Cells migrate through the primitive streak and the area between the two layers to displace the bottom (hypoblast) layer and form the endoderm. Additional cells migrate through the streak to form the new middle layer (mesoderm). All three germ layers develop into specific structures within the body as follows: Endoderm (innermost layer) gives rise to accessory digestive organs (eg, liver, pancreas) as well as to the lining (epithelium) of the digestive and respiratory tracts. Mesoderm (middle layer) gives rise to the circulatory system, muscles, bones, and parts of the urinary and reproductive systems. Ectoderm (outermost layer) gives rise to the nervous system (neurulation) and develops into the integumentary system, which includes hair, skin, nails, and the lining of the mouth, nostrils, and anus. The passage states that the notochord is a mesodermal structure. Of the choices available, only osteocytes (bone cells) are also derived from the mesoderm.

component of Bone

Compact (hard) bone is organized into structural units called osteons, or haversian systems, which are made up of lamellae (concentric rings of bone matrix) that surround a central haversian canal, a cylindrical channel that runs parallel to the long axis of bone and through which blood vessels and nerves traverse. Volkmann canals, which run perpendicular to the long axis of bone, allow the passage of blood vessels and nerves between different haversian canals Other cellular components of bone include osteogenic (osteoprogenitor) cells, osteoblasts, osteocytes, and osteoclasts. During bone remodeling, old bone is resorbed (broken down) by osteoclasts and new bone is deposited by osteoblasts. Osteogenic cells are the mitotically active stem cells in bone that initially differentiate into osteoblasts. The osteoblasts then secrete the proteins that form the unmineralized bone matrix called osteoid. Although it is primarily composed of collagen, osteoid eventually becomes mineralized through the precipitation of calcium salts on the surfaces of its collagen fibers. These deposited calcium salts mature into hydroxyapatite crystals, the mineral responsible for bone hardness. Osteoblasts continue to build successive concentric layers of bone but as the osteoid mineralizes, some osteoblasts become trapped within lacunae (spaces) in the lamellar matrix and are known as (mitotically inactive) osteocytes at this stage. Within each osteon of compact bone, lacunae connect to one another via microscopic channels called canaliculi, which allow osteocyte waste exchange and nutrient delivery Chondrocytes, however, make up the cellular component of cartilage, not bone

Conformational isomers

Conformational isomers are different forms of the same molecule that are generated as atoms rotate about their bonds. Unlike other stereoisomers, conformational isomers can rapidly interconvert by rotation without the need to break any bonds.

coordinate covalent bond

Coordinate covalent bonds, unlike covalent bonds, are formed between two atoms when both shared electrons are donated by the same atom. Such coordinate bonds are often formed between electron-poor metal ions and molecules called ligands that contain one or more electron-rich atoms with available lone-pair electrons. The coordinately bonded metal and its ligands are called a complex. As originally defined by Alfred Werner, the coordination number of a metal complex refers to the number of coordinate bonds formed between the central metal ion and its nearest neighboring atoms. When all these nearest neighboring atoms are from separate molecules or ions, the number of ligands will equal the coordination number. However, if two or more of these nearest neighboring atoms are joined to the same coordinating ligand unit, then the number ligands will not equal the coordination number. In both cases, the number of nearest neighboring atoms and coordinate bonds is unchanged, but the number of ligand units is different.

Cytotoxic T lymphocytes bind foreign antigens presented by cell surface antigen-presenting proteins, called major histocompatibility (MHC) proteins. Upon binding foreign antigens, CTLs release cytotoxins that induce apoptosis in infected cells

Cytotoxic T lymphocytes require signals from other immune cells such as antigen-presenting cells (eg, dendritic cells) and Th cells to proliferate into active immune cells that can induce apoptosis in cancerous or pathogen-infected cells.

The citric acid cycle produces only two intermediates with chiral centers:

D-isocitrate and L-malate. The first reaction in the cycle is the conversion of citrate to isocitrate by the aconitase enzyme through an intermediate called cis-aconitate. Aconitase catalyzes consecutive dehydration and hydration reactions that exchange the hydrogen atom and hydroxyl group of the second and third carbon. This isomerase activity results in the transformation of citrate, which is achiral (ie, no chiral centers), into isocitrate, which contains two new chiral centers. Fumarate is converted to malate by fumarase in a stereospecific reaction that generates only L-malate; it does not produce D-malate. Furthermore, this is a hydration reaction that splits a molecule of water and adds the hydroxyl group and hydrogen atom across the C=C double bond in fumarate.

Melted DNA strands will reanneal to form the double helix once temperature decreases, but the time it takes for complementary strands to reanneal depends on the following:

DNA length: Longer DNA molecules have more hydrogen bonds and will take more time to both melt and reanneal. pH: The physiological pH range (7.3-7.4) allows maximal hydrogen bonding between nitrogenous bases of DNA. At low pH, hydrogen bond acceptor atoms in the bases become protonated, and these protonated acceptors cannot form hydrogen bonds, causing double helix separation. In contrast, high pH causes deprotonation of hydrogen bond donors in the bases; the loss of protons results in the loss of hydrogen bonds and a destabilized double helix. Salt concentration (ionic strength): The electrostatic repulsion between negatively charged phosphate groups on the sugar-phosphate backbone destabilizes the double helix. However, this repulsion is neutralized and shielded by the binding of positively charged species in solution (eg, Na+ and Mg2+ cations). High salt concentration of the solution increases double helix stability, but low salt concentration decreases stability.

inspiration vs expiration

During inspiration, inspiratory muscles contract (eg, the diaphragm moves downward) to increase the volume of the thoracic cavity. The lungs stretch within this larger space, which leads to increased intrapulmonary volume and an inversely proportional decrease in intrapulmonary pressure. Eventually, the air pressure in the lungs falls below atmospheric pressure and, because gases flow down their pressure gradients, air will flow from the higher-pressure environment of the atmosphere into the lower-pressure environment of the lungs. This air flow persists until intrapulmonary pressure equals atmospheric pressure. In contrast, during expiration inspiratory muscles relax (eg, the diaphragm moves upward) to decrease the volume of the thoracic cavity. The lungs recoil passively to fit this smaller space, which leads to a decrease in intrapulmonary volume and an inversely proportional increase in intrapulmonary pressure (until it is higher than atmospheric pressure). Subsequently, air flows down its pressure gradient as it is forced out of the higher-pressure environment in the lungs and into the lower-pressure environment of the atmosphere.

Electrical vs chemical synapsess

Electrical synapses transfer information from one cell to another via passive ionic current flow through gap junctions. In contrast, chemical synapses use neurotransmitters to transfer information, which is a slower process.

Electromagnetic (EM) waves

Electromagnetic (EM) waves are prevalent throughout nature in a variety of different frequencies and wavelengths. EM waves are arranged by frequency (or wavelength) into the EM spectrum, which ranges from very low frequency (long wavelength) radio waves to very high frequency (small wavelength) gamma rays. When EM waves are emitted or absorbed, they behave as photons. Photon energy (E) is related to Planck's constant (h) and waveform frequency (f): E=h⋅fE=h⋅f

Osteoclasts and PTH

Endocrine glands secrete hormones that travel through the bloodstream and bind target receptors in specific tissues, evoking responses that promote the maintenance of physiological homeostasis. For example, parathyroid hormone (PTH) and calcitonin are hormones that maintain calcium homeostasis by regulating calcium absorption and bone remodeling. Specifically, a low blood calcium level stimulates the parathyroid glands to secrete PTH, which then promotes several processes to elevate the blood calcium level. One of these processes involves a PTH-induced increase in the activity of osteoclasts, which can actively break down (resorb) bone, thereby leading to release of calcium from bone into the bloodstream.

______ cells make up the interior lining of the cardiovascular system

Endothelial cells are a type of specialized epithelial cell. They form the endothelium, or interior lining of the cardiovascular system (heart and blood vessels). The endothelium provides a smooth surface that reduces the friction of blood moving through the cardiovascular system. However, substances such as erythrocytes may become attached to the endothelium, disrupting the normal flow of blood and causing vascular occlusion (ie, blockage).Endothelial cells are a type of specialized epithelial cell. They form the endothelium, or interior lining of the cardiovascular system (heart and blood vessels). The endothelium provides a smooth surface that reduces the friction of blood moving through the cardiovascular system. However, substances such as erythrocytes may become attached to the endothelium, disrupting the normal flow of blood and causing vascular occlusion (ie, blockage).

Erythrocytes,

Erythrocytes, which have a role in oxygen transport; leukocytes, which contribute to immune defense; and platelets, which are crucial in blood clotting. Plasma is the liquid portion of blood and is approximately 90% water, with the remaining 10% composed of other substances (eg, proteins, respiratory gases).

Gastrointestinal Tract Consists of the following components:

Esophagus is the tube through which ingested food, becomes a compact food mass (ie, bolus), and moves from the mouth, through the cardiac (lower esophageal) sphincter, and into the stomach. Stomach is the sac in which the food bolus is chemically (ie, via stomach cell secretions) and mechanically digested, creating a semiliquid substance (ie, chyme) that moves through the pyloric sphincter into the small intestine. Small intestine is the long, narrow tube consisting of three subdivisions (duodenum, jejunum, ileum) in which digestion of macromolecules is completed and the resulting useful substances are absorbed. Digestion of lipids in the small intestine is aided by bile, which is a nonenzymatic solution produced by liver cells and stored in the gallbladder. In addition, the pancreas secretes digestive enzymes into the small intestine along with bicarbonate, which assists in neutralizing the acidic chyme arriving from the stomach. Material unable to be digested passes to the large intestine through the ileocecal sphincter. Large intestine is the wide tube consisting of three subdivisions (cecum, colon, rectum) in which water and electrolytes are absorbed from chyme to form solid feces.

Excess post-exercise oxygen consumption (EPOC)

Excess post-exercise oxygen consumption (EPOC), or oxygen debt, represents the amount of oxygen necessary to bring the muscle back to its resting state. EPOC is equivalent to the difference between the amount of oxygen actually required for the physical activity and the total amount of oxygen used. Muscles require ATP to contract. Aerobic respiration uses oxygen to generate more molecules of ATP per metabolized glucose molecule than anaerobic glycolysis. Consequently, aerobic respiration is the primary source of ATP in muscle fibers during vigorous, long-term exercise. However, when oxygen delivery from the blood is insufficient (eg, during rapid, high-intensity exercise) and the demand for contraction exceeds the speed at which aerobic respiration can generate ATP, muscle fibers compensate by: utilizing ATP that is stored in the muscle fiber breaking down creatine phosphate, a high-energy molecule stored by muscle cells during periods of rest, to generate ATP generating ATP via anaerobic glycolysis, which yields 2 pyruvate molecules and 2 net ATP molecules per glucose molecule. In the absence of oxygen, the 2 pyruvate molecules are converted to lactic acid. continuing aerobic respiration using oxygen that is bound to myoglobin, a red-pigmented oxygen storage molecule

Oogenesis diagram

Female gametogenesis (oogenesis) is a hormone-driven process that occurs in the female gonads (ie, the ovaries) and involves mitosis and two meiotic divisions. Oogenesis begins in utero at approximately 4 weeks gestation. In the female embryo, oogonia (germ cells) are diploid stem cells that first multiply quickly via mitosis and become primary oocytes. The primary oocytes then commence the first meiotic division but become arrested at prophase I. From infancy to puberty, the ovaries are functionally inactive, and the primary oocytes remain stalled in prophase I of meiosis. The chromosome pairs are arranged in a tetrad during this phase, and their proximity allows for genetic recombination. At puberty, ovulatory cycles begin and the female is capable of reproduction. During each menstrual cycle, stimulation by follicle-stimulating hormone (FSH) followed by a surge in luteinizing hormone (LH) causes some primary oocytes to resume meiosis I. The last stage of meiosis I (telophase I) in a primary oocyte yields two unevenly divided haploid cells. One cell is the secondary oocyte, which has almost all the cytoplasm of the primary oocyte; the other is the first polar body (Choice B), which is smaller and does not develop into a mature oocyte. The secondary oocyte begins meiosis II but halts in metaphase II, and the polar body degenerates. The secondary oocyte remains frozen in metaphase II until fertilization occurs, at which point it completes its second meiotic division (telophase II) to an ootid and second polar body. The zygote that results from fertilization is diploid due to genetic contribution from both the ovum and sperm nuclei.

Factors that increase acidity

For a compound in solution, as the pH is increased, the most acidic functional group of the compound will be deprotonated first. The acidity of a functional group is determined largely by the electronegativity of the proton-donating atom and by the ability to stabilize the negative charge in the corresponding conjugate base through charge distribution (atom size) or delocalization (resonance). Negative charge is stabilized better on more electronegative atoms, and negative charge that can participate in resonance will be stabilized further by being delocalized across more than one atom. Sites that better stabilize a negative charge are more likely to be deprotonated (more acidic

Differences between mitosis and meiosis

Four daughter cells result from meiosis whereas two daughter cells result from mitosis. Haploid cells result from meiosis whereas diploid cells result from mitosis. Meiosis occurs to form gametes whereas mitosis occurs for growth and repair. Daughter cells differ from the original parent cell in meiosis whereas daughter cells are genetically identical to the original parent cell in mitosis Synapsis (close association) of homologous chromosomes occurs during meiosis but not during mitosis Two rounds of cell division occur during meiosis whereas only one round of cell division occurs during mitosis

Gas Chromatography

Gas-liquid chromatography is a technique used to separate molecules in a mixture based on their boiling points. A gas chromatograph consists of an injection port, mobile and stationary phases, a column in a heated oven, a detector, and a computer for data analysis. The mobile phase is an inert gas such as helium or nitrogen and the stationary phase is a liquid that coats a solid support on the inside of the column A small amount of a liquid mixture is injected into the gas chromatograph, and the compounds in the mixture are vaporized by heating. The vapors then travel through the column in a heated oven to the detector. The most volatile molecules (ie, low boiling points) spend more time in the gas phase than they spend interacting with the stationary phase of the column, so they rapidly migrate to the detector. However, molecules with higher boiling points condense more readily and spend more time interacting with the liquid stationary phase. These molecules make their way through the column slowly as the temperature in the oven increases. In gas-liquid chromatography, mixture components are separated primarily based on boiling point. Although the boiling point is determined by several factors (eg, polarity, intermolecular forces, molecular weight), each of these factors is already accounted for by the boiling point itself. For molecules with the same number of carbons, the boiling point increases with the increasing strength of intermolecular forces and relative polarity. However, a sufficiently large nonpolar molecule can have a higher boiling point than a small polar molecule. For example, a nonpolar 20-carbon alkane chain has a higher boiling point than a polar 4-carbon carboxylic acid (343 °C vs 164 °C) and would move through the column more slowly despite being relatively nonpolar. The column must be placed in a heated environment to allow volatile molecules to remain in the gas phase. Columns kept at room temperature would not separate the molecules.

Regulation of Glycolysis and Gluconeogensis

Glucose uptake into cells and its subsequent metabolism are controlled primarily by the hormones insulin and glucagon. The binding of insulin and glucagon at the cell membrane stimulates or suppresses the biochemical pathways involved in the uptake, breakdown, and storage of glucose. Insulin stimulates glycolysis, which consists of a series of reactions that break down glucose into pyruvate to produce ATP. Glucagon acts in the reverse by activating gluconeogenesis in the liver, which results in the synthesis of glucose from pyruvate and other precursor molecules. The well-fed state is characterized by the release of insulin in response to high levels of glucose in the blood. Insulin stimulates glucose catabolism (glycolysis) by activating the synthesis of fructose-2,6-bisphosphate (F2,6BP). F2,6BP allosterically activates phosphofructokinase-1 (PFK-1), which catalyzes the rate-limiting step of glycolysis. In the liver, F2,6BP also inhibits gluconeogenesis by allosterically inhibiting the catalytic activity of the gluconeogenesis enzyme fructose-1,6-bisphosphatase. By inhibiting gluconeogenesis in the liver, the glycolysis-gluconeogenesis balance shifts, leading to increased glycolysis and therefore increased net glucose catabolism.

Gene Therapy Using a Viral Vector

Hemoglobin is an oxygen-binding protein found within red blood cells (RBCs). Oxygen diffuses into the bloodstream via gas exchange in the lungs, binds hemoglobin, and is transported through the circulatory system to tissues throughout the body. Deleterious mutations affecting hemoglobin genes may negatively impact hemoglobin function, impairing oxygen transport. One method of treating genetic mutations is gene therapy, a technique in which a functional gene is introduced into a patient's cells to replace a mutant gene. The new gene can then be transcribed and translated into functional proteins. A common gene therapy method uses retroviral vectors to insert functional gene copies into the stem cells of patients exhibiting specific genetic mutations. In this scenario, a patient is homozygous for a deleterious mutation in a gene coding for a hemoglobin subunit. Expression of this mutant gene would likely produce a portion of the hemoglobin protein with impaired function. Because RBCs are produced from stem cells in the bone marrow, the most effective treatment for this patient would be gene therapy to introduce and activate a functional hemoglobin gene in bone marrow stem cells. This would likely lead to the production of RBCs that contain hemoglobin with normal oxygen-binding abilities.

High-performance liquid chromatography (HPLC)

High-performance liquid chromatography (HPLC) is a purification technique used for small sample sizes. The instrumentation consists of a sample injector, a column (stationary phase), a solvent under pressure (mobile phase), a detector, and a computer for data acquisition. Two types of columns—normal phase (NP) or reverse phase (RP)—can be used, depending on the relative polarity of the compounds being separated. RP-HPLC uses a nonpolar stationary phase (typically a C-18 alkyl hydrocarbon) and a comparatively polar mobile phase. In RP-HPLC, the least polar compound in a mixture will have the strongest interaction with the nonpolar stationary phase and therefore the longest retention time.

tropic vs direct hormones

Hormones can be classified by their modes of actions. Tropic hormones regulate the secretion of other hormones by acting on other endocrine glands. In contrast, direct or nontropic hormones act directly on nonendocrine tissues to cause physiological end points (eg, ADH-induced water reabsorption). The anterior pituitary releases both tropic (FSH, LH, ACTH, TSH, GH) and direct (GH, prolactin, endorphins) hormones, whereas the posterior pituitary releases only direct hormones (oxytocin, ADH).

In any purification step, some of the desired protein is lost. The total yield achieved by a purification step represents how much desired protein (in this case, protein X) is recovered. Yield can be determined by calculating the total activity of the purified protein. The activity values in an assay have arbitrary units (u) that represent some functional activity of the protein (eg, the catalytic reaction rate for enzymes):

However, a high yield of the desired protein does not mean the protein is pure (ie, that undesired proteins were removed). Protein purity is represented as specific activity (u/mg), which is a ratio of the activity of the desired protein to the total mass of protein obtained in a purification step. Consequently, specific activity increases during purification as unwanted protein is removed. Based on the table, native PAGE gives the highest specific activity (2,500 u/mg); thus, native PAGE produced the highest purity of Protein

Chemical hydrogens

Hydrogen atoms that are in identical magnetic environments within a molecule exhibit rotational or planar symmetry. These atoms are said to be chemically equivalent because they have the same atoms surrounding them, have the same chemical shift, and appear as a single signal. The splitting pattern of a signal (ie, how many peaks a signal is split into) is based on the n + 1 rule.

Hydrogen bonding is covalent or noncovalent?

Hydrogen bonding is a special type of dipole-dipole interaction in which at least one of the dipoles involves a hydrogen atom that is covalently bonded to an atom of oxygen, nitrogen, or fluorine.

Electrons always flow from _____ to -_____

In any electrochemical cell, electrons always flow from the anode (ie, the electrode where oxidation occurs) to the cathode (ie, the electrode where reduction occurs).

Synaptic transmission via ligand-gated ion channels

In chemical synapses, when an action potential (AP) reaches the axon terminal of the presynaptic neuron, the terminal membrane depolarizes and causes voltage-gated Ca2+ channels to open. Extracellular Ca2+ ions flow down their electrochemical gradient into the axon terminal and stimulate neurotransmitter-containing synaptic vesicles to fuse with the presynaptic membrane and release their contents into the synaptic cleft by exocytosis. The neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic cell membrane, which can be ligand-gated ion channels or G protein-coupled receptors (GPCRs). In most cases when a specific ligand (neurotransmitter) binds to its corresponding ligand-gated ion channel on the postsynaptic neuron, the channel changes its conformation to the open state. Depending on the type of channel and the environmental conditions (eg, membrane potential) in which the channel is found, ionic movement across the membrane results in either postsynaptic depolarization (excitation) or hyperpolarization (inhibition). Because Ca2+ and Na+ concentrations are typically greater outside the neuron than inside, if ligand-gated ion channels permeable to these ions were to open in response to neurotransmitter release, both Ca2+ and Na+ would rush into the neuron and depolarize the membrane. This depolarization, if summed with other excitatory signals, would contribute directly to the generation of a postsynaptic AP.

Crossing over during meiosis

In eukaryotes, reproductive cells (gametes) are produced via meiosis, during which a diploid (2n) parent cell divides to produce four genetically distinct haploid (n) daughter cells. Meiosis has four phases (like mitosis) but these phases occur in two successive cell division stages (meiosis I and II). In prophase I of meiosis, homologous chromosomes line up side-by-side during synapsis. Because each homologous chromosome consists of two identical (sister) chromatids, this adjacent chromosomal alignment forms a tetrad (ie, four chromatids total). Tetrads arise when a synaptonemal complex (protein structure) forms between homologous chromosomes and holds them together tightly. The tetrad structure allows physical contact between the paternal and maternal chromosomes at the chiasma, a point where a chromosome segment can break off and rejoin with the opposite homologous chromosome. This exchange of DNA is the hallmark feature of the process called crossing over. Crossover events result in daughter cells with chromosomes containing combinations of alleles that differ from those in the parent cell, leading to eukaryotic genetic recombination and increased genetic variation. Because crossover events produce genetically unique gametes, the offspring that develops after fertilization is genetically different from either parent, leading to increased genetic variation

color wheel

In highly conjugated systems, the difference in energy between the ground and excited states of the electrons is equal to the energy of a particular wavelength of visible light. Photons of this wavelength are absorbed by the molecule, causing an electron to enter the excited state. The remaining wavelengths are either reflected or transmitted and are ultimately perceived by the eye as various colors. In general, the perceived color of a substance is complementary to the color of the wavelength that is maximally absorbed by that substance. For example, a molecule that absorbs blue light will appear orange and vice versa. When the basic colors of the visible spectrum (red, orange, yellow, green, blue, and violet, or ROYGBV) are arranged in a wheel with red and violet next to each other, a color's complement is the color directly across fro

Infrared Spectroscopy IR absorption ranges

In infrared (IR) spectroscopy, a sample is irradiated with IR light, and a spectrometer detects and records the percentage of radiation that passes through the sample over a range of frequencies. The IR spectrum of a compound indicates the types of bonds and functional groups present in a compound. Different functional groups absorb IR radiation at different frequencies, and therefore the signal from each group appears in a particular region of the IR spectrum. Although individual molecules may have distinct absorption spectra in the fingerprint region (700-1500 cm−1), each functional group on the molecule will still absorb in its characteristic IR region regardless of the global structural features of the molecule.

Ionic radii

Ionic radii tend to decrease across a period (row) of the periodic table (left to right) and increase moving down a group (column). This trend occurs for metal cations, and then resets and repeats for anions beginning near the division between metals and nonmetals, past which anions tend to preferentially form. Losing electrons to form a cation causes the remaining electrons to experience a greater effective nuclear charge (Zeff), pulling the electrons closer to the nucleus. Conversely, gaining electrons to form an anion produces greater electronic repulsion and nuclear shielding (lesser Zeff), which pushes electrons farther from the nucleus. Notes: Cations are always smaller than the neutral atom and anions are always larger.

PI and amino acid charge

Ionizable side chains that contain oxygen or sulfur (Y, C, E, and D) are negatively charged when deprotonated and tend to decrease pI. For side chains that can be negatively charged, a lower pKa correlates with a stronger effect on pI. Therefore, aspartate and glutamate cause the greatest decreases in pI. Ionizable side chains that contain nitrogen (R, K, and H) are positively charged when protonated and tend to increase pI. Side chains that can be positively charged have a greater effect if the pKa is high, and therefore arginine and lysine cause the greatest increases in pI. All other side chains are nonionizable and do not affect pI.

effective nuclear charge and ionization energy correlation

Larger values of Zeff create a stronger attraction that takes more energy to overcome. Consequently, atoms with more core electrons (ie, more charge screening) have a lower Zeff, making it easier to remove a valence electron. Larger values of Zeff create a stronger attraction that takes more energy to overcome. Consequently, atoms with more core electrons (ie, more charge screening) have a lower Zeff, making it easier to remove a valence electron.

How do liver cells respond to insulin in regards to lipid synthesis

Liver cells respond to insulin by increasing their rates of lipid synthesis. In the mitochondria, insulin activates pyruvate dehydrogenase (PDH), which converts pyruvate to acetyl-CoA. The accumulated acetyl-CoA is transported to the cytoplasm through the citrate shuttle, in which acetyl-CoA combines with oxaloacetate to form citrate. Citrate can then exit the mitochondria. In the cytoplasm, citrate is converted back to acetyl-CoA and oxaloacetate. Multiple acetyl-CoA units can then be combined to form fatty acyl groups.

Effects of aldosterone on kidney function

Located in the posterior abdomen on the left and right sides of the body, the kidneys are two bean-shaped organs that participate in excretory, metabolic, and homeostatic functions. The homeostatic functions of the kidneys occur primarily through the filtration of blood and the selective secretion or reabsorption of filtered contents. Filtration of blood by the kidneys yields a fluid (called the filtrate) that undergoes significant changes in volume and composition prior to excretion as urine. Nutrients such as glucose and amino acids are reabsorbed into the body, and toxins are secreted. The majority of filtered sodium (Na+) and water (H2O) is reabsorbed. However, the reabsorption of sodium and water is subject to some degree of adjustment based on physiological conditions. For example, the hormone aldosterone, which is secreted by the adrenal cortex in response to high serum potassium (K+) and low blood pressure (via the renin-angiotensin system), acts on the kidney to promote sodium reabsorption and potassium secretion. However, more sodium is reabsorbed than potassium is secreted. Consequently, an ion gradient is generated between the filtrate and the interstitial fluid in the adjacent interstitial space, causing water to be reabsorbed into the interstitial fluid (and eventually the bloodstream) via osmosis. As a result, blood volume and therefore blood pressure increase.

kinesin vs dynein

Microtubules are structural cytoplasmic filaments composed of tubulin subunits. These filaments have a number of critical functions, including serving as tracks for intracellular transport of organelles and vesicles. The movement of intracellular cargo along microtubules is mediated by two motor proteins: Kinesin: Moves intracellular cargo along microtubules in anterograde axonal transport (ie, away from the nucleus and toward distal sites). Dynein: Participates in retrograde axonal transport of intracellular cargo (ie, from distal sites toward the nucleus) (Choice D). According to the question, mitochondria are transported from the cell body toward the presynaptic terminal. Because mitochondria are being transferred from the nucleus and toward the synaptic terminal, this anterograde transport is most likely being performed by kinesin motors moving along the microtubules

Morphogenes

Morphogens (eg, Notch) are signaling molecules that change patterns of embryonic cell differentiation in a concentration-dependent manner. Cells that respond to morphogens (due to the presence of receptors) are known as competent cells. After morphogens are released from signaling cells, the molecules diffuse from one region of the embryo to the other, creating a concentration gradient. Some morphogens are paracrine factors, acting on cells that are close to the signaling cell. Other morphogens signal via direct contact mechanisms, in which a ligand attached to the plasma membrane of the signaling cell interacts with a receptor on the membrane of an adjacent cell.

Muscle Fiber Types

Muscle fiber types include the following: Slow-twitch (type 1) oxidative fibers contract at a slow rate due to the lesser frequency at which the myosin heads hydrolyze ATP during each contractile cycle. These fibers produce ATP via aerobic respiration. Therefore, they contain many mitochondria that use oxygen in the electron transport chain to produce large amounts of ATP (energy), making these fibers more fatigue resistant. Type 1 fibers receive oxygen from their extensive capillary networks and high concentrations of myoglobin. Fast-twitch fibers achieve more rapid contraction rates (complete more contractile cycles) than slow-twitch fibers because they can hydrolyze ATP much faster. These fibers are classified as follows: Fast glycolytic (type 2X) fibers rely primarily on nonoxidative (anaerobic) glycolysis for ATP production. Accordingly, these fibers fatigue more easily due to the acidosis caused by H+ accumulation from anaerobic ATP hydrolysis. Because type 2X fibers generally contain very few mitochondria and require much less oxygen than oxidative fibers, they exhibit low myoglobin concentration and less extensive capillary networks. Fast oxidative-glycolytic (type 2A) fibers use both oxidative (ie, aerobic respiration) and nonoxidative processes (ie, anaerobic glycolysis) to generate ATP, making them moderately susceptible to fatigue. Like type 1 fibers, these fibers also receive oxygen from abundant myoglobin reserves and extensive capillary networks.

neurulaton

Neurulation is the formation of the nervous system in vertebrate organisms. Following gastrulation (formation of the three germ layers), the notochord, a mesodermal cylindrical structure, releases signals promoting the ectoderm above to thicken and form the neural plate. The neural plate folds inward, forming the neural groove, and the edges of the plate (the neural folds) converge to create the neural tube. The neural tube, which is the precursor of the central nervous system (CNS: brain and spinal cord), then pinches off the ectoderm. The remaining sections of the neural folds not included in the neural tube comprise the neural crest. Neural crest cells migrate away from the tube and toward the periphery of the embryo to give rise to most of the peripheral nervous system (PNS). Note that although somatic motor neurons are part of the PNS, their cell bodies originate in the CNS.

Does alternative splicing produces multiple protein products by producing distinct mRNA molecules from disticts genes (i.e distict segments of DNA)?

No, alternative splicing produces multiple protein products by producing distict mrNA molcules from the same gene!!

Proline and glycine IN PROTIEN STRUCTURE

Proline and glycine are often found in loops and linker regions between α-helices and β-sheets, particularly at sharp turns (eg, beta turns). Proline is unlikely to be found within an α-helix because it is structurally rigid and introduces a kink in the chain that is useful for sharp turns but disrupts α-helices. In addition, the backbone amide of a proline residue connects back to its side chain to form a ring structure and is therefore unable to participate as a hydrogen bond donor. Glycine has the smallest side group of all the amino acids (a hydrogen atom) and is quite flexible. Although ideal for sharp turns, this flexibility causes α-helices to be too "floppy" and disrupts the structure

Prostaglandins

Prostaglandins are nonhydrolyzable, 20-carbon (eicosanoid) lipids involved in autocrine and paracrine signaling. They are derived from arachidonic acid and often help mediate localized inflammatory responses.

protein processing

Proteins that are embedded in the plasma membrane traveled through the secretory pathway to arrive there. Translation of mRNA to proteins always begins in the cytosol, but proteins intended for the secretory pathway (eg, the receptors to which viruses such as AAV2 bind) have an N-terminal sequence called a signal sequence. Once the signal sequence is recognized, the ribosome is transported to the rough endoplasmic reticulum (RER) (Choice A), where the protein is either translocated across the RER membrane (secreted proteins) or embedded into the membrane (integral membrane proteins). In the RER, some post-translational modifications may occur, including glycosylation, disulfide bond formation, phosphorylation, and protein cleavage. The RER then packages proteins into vesicles and sends them to the Golgi apparatus (Choice B), where they are further processed. Finally, the Golgi packages proteins destined for the plasma membrane into secretory vesicles (Choice D), which fuse with the plasma membrane. Proteins that were initially embedded in the RER membrane frequently end up embedded in the plasma membrane as receptor proteins. The peroxisome is not part of the secretory pathway and is not involved in protein transport to the cell surface. Instead, peroxisomes contain various oxidoreductase enzymes and function to help maintain the proper oxidation state within cells. Proteins in the peroxisomal lumen were translated entirely in the cytosol and imported. Therefore, the proteins that bind AAV2 most likely do not pass through the peroxisome on their way to the cell surface.

Proton nuclear magnetic resonance spectroscopy (1H NMR)

Proton nuclear magnetic resonance spectroscopy (1H NMR) detects protons in a molecule when an external magnetic field and radio frequency are applied to a sample. The protons align their magnetic field either with (low-energy α spin state) or against (high-energy β spin state) the external magnetic field. Radio waves excite the protons from the α to the β spin state, and the peaks on the spectrum represent the energy difference between the spin states, known as the effective magnetic field

Radioactive beta decay

Radioactive beta decay can occur in three forms: β−-decay (electron emission), β+-decay (positron emission), and electron capture. In β−-decay, a neutron converts to a nuclear proton and emits an electron. In β+-decay, a nuclear proton converts to a neutron (the opposite of β−-decay) and ejects a positron (an electron with a positive charge). In electron capture, a proton captures an electron near the nucleus and converts to a neutron without a positron or electron emission. In all three forms of beta decay, the mass number remains unchanged whereas the atomic number either increases (β−-decay) or decreases (β+-decay and electron capture) by 1. As the atomic number changes, the identity of the element changes accordingly.

Receptor tyrosine kinases (RTKs)

Receptor tyrosine kinases (RTKs) are one of the most common types of receptor enzymes. Upon ligand binding, RTKs dimerize. Each RTK in the dimer then phosphorylates one or more tyrosine residues on the intracellular domain of the other RTK. This action ultimately activates a pathway that alters the cell's behavior.

Retrovirus infection

Retroviruses are unique in that they are enveloped and carry two identical +ssRNA molecules. Successful viral replication depends on enzymes that allow its RNA viral genome to enter the nucleus and integrate with the host's DNA genome. Retroviruses enter host cells through endocytosis, which allows the capsid and envelope to uncoat (ie, disassemble). Uncoating releases the viral genetic material inside the host cell. RNA viruses such as HXV must then convert their genomes from +ssRNA into double-stranded DNA (dsDNA) before integration into the host genome can occur. The generation of DNA using an RNA template is accomplished using reverse transcriptase (ie, RNA-dependent DNA polymerase), which is encoded in the viral genome. Once the dsDNA has been integrated, the viral genome is replicated along with the host cell's own DNA as a lysogenic provirus. Consequently, the original cell containing the integrated viral genome divides and produces descendants that are also infected. "Retroviruses are enveloped, positive-sense, single-stranded RNA viruses that convert their RNA genomes into double-stranded DNA using the enzyme reverse transcriptase. During their lysogenic cycles, retroviruses enter the nucleus and integrate their reversed transcribed DNA with the host genome."

Starvation response: lipid metabolism

Starvation causes a significant decrease in blood glucose levels and stimulates the release of the hormone glucagon, which signals for the release of glucose from glycogen stores (glycogenolysis). To preserve glucose for the tissues that require them, the liver also begins to break down triacylglycerol reserves. Triacylglycerols are esters of glycerol with three fatty acid chains that function as the main energy reserves in animals. These storage lipids are formed in fat cells, or adipocytes, and yield the most ATP when broken down in the liver to glycerol and free fatty acids. Glycerol is rapidly converted to glyceraldehyde 3-phosphate for glucose synthesis (gluconeogenesis) while free fatty acids enter the mitochondria, where they are oxidized to generate acetyl-CoA for the citric acid cycle to produce energy. Excess acetyl-CoA that accumulates beyond what is needed for the liver can be converted to ketone bodies such as acetoacetate and 3-hydroxybutyrate, which are then exported into the circulation. Although the brain primarily uses glucose as a fuel source, it can also use ketone bodies as an energy source when needed.

Superheating and boiling chips

Superheating occurs when a liquid is heated above its boiling point but does not boil. Surface tension can cause superheating because it can inhibit the formation of bubbles. As bubbles attempt to form, surface tension causes a local increase in vapor pressure that surpasses the ambient pressure, allowing the liquid to heat beyond its boiling point. This phenomenon can cause the formation of large bubbles at the surface, which can erupt violently and eject the hot liquid from the distillation flask in a process called bumping. This effect is difficult to overcome without scratches or crevices in the container where smaller bubbles can begin to form. Boiling chips are made of nonreactive porous material and provide nucleation sites where small bubbles of vapor can form. This effect overcomes the surface tension and allows the liquid to boil evenly at its normal boiling temperature, thereby preventing superheating.

negative selection

T lymphocytes are initially produced in the bone marrow before being transported to the thymus, a specialized lymphoid organ where T-lymphocyte maturation occurs. A process called negative selection eliminates any T lymphocytes that recognize self-antigens (ie, those that would induce apoptosis in healthy cells). Negative selection is carried out by thymic cells (not Th cells) and would not affect the function of CTLs able to recognize foreign antigens (eg, CTAs).

keto-enol tautomerization

Tautomerization is a type of isomerization that involves the transfer of hydrogen from one position to another within a molecule and the movement of a double bond to an adjacent atom. These two forms, called tautomers, are in equilibrium. Tautomerization frequently involves a keto form (compound with C=O) as the major tautomer whereas the enol form is the minor tautomer. Tautomers are classified as constitutional isomers rather than resonance structures because a bond is broken during the hydrogen transfer to yield a different compound. On the other hand, resonance structures are forms of the same compound in which electrons move from one atom to another without breaking any sigma bonds.

Tollen's Test

The Tollens test (silver mirror test) is a qualitative test that detects reducing sugars. These sugars can reduce the Tollens and other reagents and, as a consequence, are themselves oxidized. Structurally, reducing sugars can be recognized by having a free anomeric carbon. In cyclic sugars, anomeric carbons can be distinguished as free if at least one of the attached oxygens is part of a hydroxyl group, thereby showing that particular anomeric carbon is not involved in a glycosidic bond. During the oxidation of reducing sugars, cyclic sugars are linearized first (if possible) and then the carbonyls of linear sugars are oxidized. The aldehydes of aldoses can be directly oxidized to carboxylic acids; however, the ketones of ketoses must undergo keto-enol tautomerization before the sugar can be oxidized. During tautomerization, the ketone on carbon 2 of the ketose tautomerizes to form a double bond between carbon 1 and carbon 2. Because both carbon 1 and carbon 2 have alcohols, this intermediate is known as an enediol. Tautomerization of the enediol can reform a carbonyl (this time on carbon 1) to form the aldehyde of an aldose sugar, which can then be oxidized.

Neutral salts such as NaCl, which dissociate in solution, can disrupt salt bridges by forming ionic bonds with amino acids.

The acidic and basic side chains of amino acids form ionic bonds referred to as salt bridges, which contribute to tertiary and quaternary structure. High salt concentrations can disrupt salt bridges and cause proteins to become denatured (unfold). The loss of three-dimensional structure in denatured proteins results in a loss or reduction of function.

stress response

The adrenal glands are located atop each kidney. Each adrenal gland can be subdivided into two portions: a central inner portion called the adrenal medulla, and an outer portion called the adrenal cortex, which is responsible for secreting corticosteroids (eg, cortisol, aldosterone). The hypothalamic-pituitary-adrenal pathway (HPA axis) controls the secretion of glucocorticoids from the adrenal cortex as follows: The hypothalamus secretes corticotropin-releasing hormone (CRH) in response to low glucocorticoid levels and increased stress. CRH acts on the anterior pituitary, which causes the release of adrenocorticotropic hormone (ACTH). ACTH stimulates the adrenal cortex to synthesize and release cortisol. Cortisol targets tissues (eg, muscle and liver) to increase the ability to cope with stressors. In addition, cortisol functions as a negative feedback signal by inhibiting the secretion of CRH and ACTH. A drug that blocks the release of ACTH would also block the stimulatory effect of ACTH on the adrenal cortex, thereby decreasing the secretion of cortisol.

Initial digestion of triglycerides, carbohydrates and polypetides

The components of the gastrointestinal tract include the oral cavity, esophagus, stomach, small intestine (SI), and large intestine. Initial mechanical digestion of food occurs via mastication by the teeth in the oral cavity and, at the same time, saliva and mucus secreted by the salivary glands lubricate ingested food. Saliva, a fluid substance, contains enzymes for initial chemical digestion of some macromolecules. These enzymes include lingual lipase, which hydrolyzes triglycerides into free fatty acids and diglycerides, and salivary amylase, which hydrolyzes the polysaccharide starch into the disaccharide maltose. Further chemical digestion of these macromolecules occurs in the SI. The muscles of the oral cavity compress mechanically digested food into a bolus (ball), which can be swallowed. This bolus passes from the oral cavity to the pharynx (throat) and past the upper esophageal sphincter. Next, the bolus enters the esophagus, a passageway for food to be carried to the stomach. Esophageal peristalsis propels the bolus in the direction of the stomach. In the stomach, gastric chief cells release the zymogen (inactive) pepsinogen, which is converted to its active form, pepsin, upon mixing with hydrochloric acid in gastric juice. Pepsin is a proteolytic enzyme responsible for the initial digestion of polypeptides into smaller peptides. Accordingly, initial triglyceride, carbohydrate, and polypeptide digestion is performed by lingual lipase, salivary amylase, and pepsin, respectively.

"down concentration gradient" vs "up concentration gradient"

The concentration of molecules within the cell is usually different than the concentration of molecules outside the cell, and molecules may travel down their concentration gradient (from high to low concentration) or against their concentration gradient (from low to high concentration).

Galileo Thermometer

The density of a substance is defined as the mass it contains per unit of volume it occupies. The exact density of a substance, however, can slightly vary with temperature due to minute changes in volume because materials tend to expand when heated and contract when cooled. Materials also physically arrange according to density. For example, when a solid object is placed into a liquid, the object will float if it has a density less than that of the liquid, but it will sink if its density is greater than that of the liquid. Initially, at 25 °C, the mass-to-volume ratio (ie, density) of the sealed glass bulb exactly matches that of the solution in the cylinder. As the temperature of the solution in the cylinder decreases, the liquid contracts slightly and the density of the cylinder solution increases (ie, same mass occupying a smaller, contracted volume). Because the glass bulb acts like an isolated system, its density changes very little compared with that of the cylinder solution. Accordingly, the density of the cooling solution in the cylinder becomes greater than that of the bulb, causing the bulb to begin to float. This is the basis for the function of the Galileo thermometer.

NADH in electron transport chain

The electron transport chain (ETC) is a series of protein complexes in the inner mitochondrial membrane that facilitate transfer of high-energy electrons from reduced energy carriers to lower-energy acceptors. The energy released by this series of redox reactions drives ATP synthesis. NADH carries two electrons in the form of a hydride H− ion, and these electrons enter Complex I of the ETC to reduce ubiquinone (UQ) to ubiquinol (UQH2). UQH2 then travels through the lipid bilayer to Complex III, where the electrons from a single UQH2 can reduce up to two cytochrome c (cyt c) molecules. These cyt cred molecules then travel through the intermembrane space to Complex IV, where they deposit electrons one by one to oxygen, progressively reducing it to water once four electrons have been deposited. Note that although electrons can also be deposited into the ETC via FADH2 in Complex II, electrons from NADH alone are sufficient to reduce oxygen to water. NADH is a two-electron carrier. Because turning O2 into water requires four electrons per oxygen molecule, a minimum of two NADH molecules would need to pass their electrons through the ETC to fully reduce O2

endothelium i

The endothelium is the one-cell-thick layer of specialized epithelial cells (ie, endothelial cells) that line the interior of the cardiovascular system, which includes the heart, arteries, capillaries, and veins. This layer of cells is in direct contact with the blood in the lumen (inner cavity) and provides a relatively smooth, friction-reducing surface that enables the efficient movement of blood through the vasculature. The endothelium also acts as a barrier that regulates the exchange of substances between the blood and nearby tissues. For example, in response to inflammatory chemicals released during an infection, endothelial cells facilitate the movement of white blood cells out of the bloodstream to the affected tissue.

To convert the potential energy of fatty acids into the metabolic currency ATP or GTP, fatty acids have to be converted to what first?

The fatty acids bound to glycerol in triglycerides (eg, in adipose tissue cells) represent the body's densest store of metabolic potential energy. These fatty acids can be released from glycerol by lipases, thereby contributing to the "free" (ie, nonesterified) fatty acids present in body fluids. To convert the potential energy of fatty acids into the metabolic currency (eg, ATP, GTP) used by cells, free fatty acids are first converted to fatty acyl-coenzyme A (CoA) molecules, after which they are progressively shortened during the process of fat oxidation. Each round of fatty acid shortening produces acetyl-CoA and the cofactors NADH and FADH2.

female reproductive system

The female reproductive system is responsible for producing female gametes (ie, ova) and protecting, nourishing, and providing support to a developing embryo and fetus. The system includes the following internal structures: The ovaries are reproductive organs that produce oocytes (immature gametes) via oogenesis and secrete hormones (eg, estrogens, progesterone, inhibin). The uterine tubes (fallopian tubes, oviducts) are tubes connecting each ovary to the uterus and are the typical location of fertilization (Choice D). The uterus is muscular organ responsible for protecting and nourishing the embryo and fetus. The uterus is lined with an inner layer called the endometrium, which changes in thickness at different points in the monthly uterine cycle. The uterus also includes a thick layer of smooth muscle (ie, myometrium) involved in contractions during childbirth.The cervix is the most inferior portion of the uterus and serves as the opening into the vagina (Choice A). During childbirth, the cervix thins and the fetus passes through the cervix into the vagina. The vagina is a muscular tube that functions in the elimination of menstrual fluids during the menstrual cycle, the reception of the male penis during sexual intercourse, and as the final segment of the birth canal during delivery.

Functions of the GI tract

The gastrointestinal tract is composed of the esophagus, stomach, small intestine, and large intestine. After undergoing initial breakdown in the mouth, ingested food begins its passage through the gastrointestinal tract by traveling down the esophagus to the stomach where chyme, a semifluid mixture of partially digested food, is formed. This chyme then exits the stomach to begin transit through the intestines. First, in the small intestine, intestinal and pancreatic enzymes break down macromolecules, which are then absorbed via diffusion through absorptive cell membranes or through intestinal transporters. Next, food enters the large intestine, the site where additional water absorption occurs and where microbial communities (gut flora) synthesize vitamins and metabolize remaining carbohydrates. In this scenario, the participant consumes a large meal but is unable to sufficiently absorb nutrients (ie, exhibits malabsorption). Nutrient absorption in the gastrointestinal tract is influenced by several factors, including: The presence and diversity of fatty acid-producing bacteria in the large intestine. These bacteria metabolizeundigested carbohydrates from the small intestine into short-chain fatty acids, which are absorbed and used as additional energy sources. A decrease in these bacterial species would lead to decreased absorption of additional fatty acids as nutrients The small intestine's surface area. Large folds in the intestine's epithelial lining slow the movement of chyme through the intestinal tract. In addition to these large folds, villi (fingerlike projections extending from the lining) and microvilli (smaller fingerlike extensions of individual absorptive cells) maximize the time and surface area available for nutrient absorption. Malabsorption is sometimes caused by structural damage (eg, villi destruction) that decreases small intestinal surface area, which thereby impairs nutrient absorption The functions of intestinal proteins. Structural proteins, digestive enzymes, and nutrient transporters work synergistically to break down and absorb nutrients within the gastrointestinal tract. Because antibodies mark cellular materials for destruction by cells of the immune system, production of antibodies against intestinal proteins would likely cause the destruction of these proteins, damaging the intestinal tract and decreasing nutrient absorption (Choice C). Intestinal nutrient transporters facilitate nutrient absorption from the intestinal tract into the body. Therefore, increasednutrient transporter activity would increase (not decrease) nutrient absorption.

heart pathway

The heart is a muscular structure that uses strong contractions to propel blood continuously throughout the circulatory system. The heart is composed of two separate pumps that contract simultaneously; the right side of the heart pumps blood to the lungs, and the left side of the heart pumps blood to the rest of the body. The heart has four chambers: The left and right atria are receiving chambers, whereas the left and right ventricles are pumping chambers that supply the force necessary to propel blood through the circulatory system. The atrioventricular (AV) and semilunar (SL) valves prevent the backward flow of blood into the atria and ventricles, respectively. Accordingly, blood flows through the circulatory system as follows: Deoxygenated blood from body tissues enters the right atrium via the (superior and inferior) vena cavae The right atrium contracts, forcing the deoxygenated blood through the tricuspid valve and into the right ventricle. The right ventricle contracts to propel the blood through the pulmonary valve and into the pulmonary arteries The pulmonary arteries carry blood from the heart to the capillary beds of lung alveoli, where gas exchange occurs. In pulmonary capillary beds, the blood unloads carbon dioxide and loads oxygen (ie, becomes oxygenated) and returns to the left atrium via the pulmonary veins. The left atrium contracts, pushing the oxygenated blood through the bicuspid (mitral) valve and into the left ventricle The left ventricle contracts to pump blood through the aortic valve to the rest of the body via the aorta. The blood flowing through systemic blood vessels delivers nutrients and oxygen to the body tissues before returning to the heart.

Ketone and Aldehyde Nomencluture

The highest-priority group in Compound 2 is an aldehyde, and the compound is named using the suffix -al. The longest continuous chain containing the carbonyl (ie, the C=O bond) is seven carbons (prefix hept-) and is numbered so the carbonyl carbon is carbon 1. The substituent on carbon 3 is an isobutyl group and is denoted in front of the parent chain name to give the name 3-isobutylheptanal. The highest-priority group in Compound 3 is a ketone, and the compound is named using the suffix -one. The longest continuous chain containing the carbonyl is six carbons (prefix hex-) and is numbered so that the carbonyl carbon has the lowest number possible (ie, carbon 2, in this case). The ethyl substituent on carbon 3 and the methyl substituent on carbon 5 are denoted in alphabetical order in front of the parent chain name to give the name 3-ethyl-5-methylhexan-2-one

Bone structure

The human skeleton can be divided into axial (ie, skull, spine, ribcage) and appendicular (ie, limb) components. Long bones, one of the four bone types, are aptly named based on their appearance: their length is greater than their width. The long bones (eg, femur) serve to provide a framework for movement. The structure of long bones includes the following: Epiphyses are rounded ends that have joint surfaces covered by articular cartilage. The diaphysis is the hollow shaft (medullary cavity) filled with bone marrow (primarily of the yellow type in adulthood). Metaphyses are the regions where the diaphysis and epiphyses meet. The epiphyseal (growth) plate, a cartilaginous structure that lies between the epiphyses and metaphyses, is present only during childhood and serves as the site of longitudinal growth. When growth ceases, the growth plate is replaced with mature bone, forming the epiphyseal line. The periosteum is a thin layer of connective tissue that covers and protects long bones but does not cover joint surfaces.

The hypothalmic pituitary thyroid axis

The hypothalamic-pituitary-thyroid axis controls the secretion of thyroid hormones from the thyroid gland through endocrine signaling as follows: In response to low thyroid hormone levels or a decrease in body temperature, the hypothalamus secretes thyrotropin-releasing hormone (TRH). TRH acts on the anterior pituitary, which causes the release of thyroid-stimulating hormone (TSH). TSH binds to TSH receptors on cells of the thyroid gland, stimulating these cells to release thyroid hormones. Upon stimulation by TSH, thyroid gland cells secrete two types of thyroid hormones: triiodothyronine (T3) and thyroxine (T4). When released, T3 and T4 affect nearly every cell in the body by increasing cellular metabolism. These hormones also function in a negative feedback loop by inhibiting the secretion of TRH and TSH.

Ant. Pituitary

The hypothalamus controls the anterior lobe of the pituitary gland by releasing signaling molecules into the hypophyseal portal system, a localized network of blood vessels that bridges the hypothalamus and anterior pituitary. These signaling molecules promote or inhibit the release of specific hormones into the systemic circulation by the anterior pituitary gland. For example, corticotrophin-releasing hormone (CRH) released by the hypothalamus stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH) into the systemic circulation. ACTH then acts on the adrenal glands to promote synthesis and secretion of glucocorticoids, completing the neuroendocrine pathway that regulates the serum level of cortisol and other glucocorticoids.

innate vs adaptive immunity

The immune system, divided into innate and adaptive immunity, comprises several types of immune cells, all of which are produced from bone marrow stem cells These immune cells monitor the body for foreign pathogens by circulating throughout the blood and lymph. Cells of the innate immune system rapidly and nonspecifically mount immune responses against foreign antigens. Innate immune cells can respond to many types of foreign antigens and cellular stress signals to mount immediate responses against invading pathogens. In contrast, cells of the adaptive immune system recognize and bind only one type of foreign antigen, mounting specialized immune responses against invading pathogens. Adaptive immune cells must be activated prior to mounting an immune response, a process that may take several days These adaptive immune cells include: T lymphocytes, which recognize and bind specific foreign antigens displayed by specialized surface proteins called major histocompatibility complex (MHC) proteins on other cells. T lymphocytes include both helper T cells and cytotoxic T cells. B lymphocytes, which are activated by binding and phagocytizing foreign antigens. Within B lymphocytes, these antigens are broken down and MHC proteins bind the antigen fragments, transporting them to the cell surface. Generally, helper T cells bind foreign antigens presented by B lymphocyte MHC proteins and release signaling molecules that stimulate B lymphocytes to divide and differentiate into antibody-secreting plasma cells and memory B cells, which can respond more rapidly in the event of a future infection.

Digestion of Lipids in the Small Intestine

The liver synthesizes bile, a nonenzymatic solution stored in the gallbladder and released into the small intestine to aid in the mechanical digestion of lipids. Bile is composed of bile salts, bile pigments (eg, bilirubin), and cholesterol. Bile salts act as detergents to solubilize fats during digestion; they possess both a hydrophobic region that associates with the surface of lipids and a hydrophilic region that associates with water. Consequently, bile salts break down large lipid globules into smaller droplets (micelles) in a process known as emulsification. Emulsification is an example of mechanical digestion, a nonenzymatic process that physically breaks down food particles into smaller pieces. Additional examples of mechanical digestion include chewing in the mouth and churning in the stomach due to peristaltic waves. Chemical digestion is carried out by acids and enzymes and involves the cleavage of chemical bonds within macronutrients to form simpler compounds that can be absorbed. Emulsified lipids have increased surface area on which pancreatic lipase can exert its enzymatic effect (ie, chemical digestion of lipids). As a result, lipase secreted from the pancreas facilitates the chemical digestion (enzymatic hydrolysis), not mechanical digestion, of triglycerides within micelles into free fatty acids and monoglycerides. The salivary glands are exocrine glands in the mouth that secrete saliva, a lubricating fluid containing the enzymes lipase and amylase. Lingual lipase facilitates the chemical, not mechanical, digestion of lipids. In contrast, salivary amylase hydrolyzes (chemically digests) the polysaccharide starch into the disaccharide maltose.

Explain bone marrow, thymus, lymph nodes and spleen as it relates to the lymphatic system

The lymphatic system is particularly important to the immune response and includes the following lymphoid tissues and organs, which facilitate immune cell proliferation and function: The bone marrow, a spongy tissue lining the inside of bones, is responsible for the production of red blood cells and white blood cells (eg, lymphocytes) from hematopoietic stem cells. The thymus receives immature T lymphocytes migrating from the bone marrow and facilitates their maturation. During this process, any T lymphocytes that recognize self-antigensdie, preventing the release of lymphocytes able to mount attacks against the body's own tissues. However, T lymphocytes that do not bind self-antigens mature and enter the blood and lymph, where they bind foreign antigens and mount immune responses. Lymph nodes, organs clustered along lymph vessels, filter lymph as it flows through the lymphatic system. Macrophages housed within lymph nodes identify a variety of pathogens in lymph and destroy them via phagocytosis. In addition, B lymphocytes and T lymphocytes bind specific foreign antigens in lymph, inducing immune responses against invading pathogens. The spleen has extensive capillary networks through which blood is filtered. White blood cells housed within the spleen recognize and bind foreign antigens in the blood, mounting immune responses against these circulating pathogens. In addition, spleen macrophages remove and destroy old and damaged red blood cells. Platelets and other white blood cells are also stored in the spleen and released into the blood as needed.

The male reproductive system is responsible for producing sperm (ie, gametes) and includes the following structures:

The male reproductive system is responsible for producing sperm (ie, gametes) and includes the following structures: Testes: reproductive glands that produce sperm during spermatogenesis. Epididymis: a long, tightly coiled tube on the posterior of each testis; immobile sperm produced by the testes become mature and motile within this tube. Mature sperm are stored in the epididymis until release (Choice B). Ductus (vas) deferens: a long, muscular tube that transfers mature sperm to the urethra (Choice C). Seminal glands: accessory glands that produce the largest portion of seminal fluid (Choice D). Prostate: a gland that produces prostatic fluid containing enzymes necessary to prevent the coagulation of sperm in the vagina. Bulbourethral (Cowper's) glands: glands that secrete thick, alkaline mucus to lubricate the tip of the penis. The alkalinity of the mucus neutralizes acids in the urine to protect the sperm from the acidic environment of the urethra. Penis: an exterior organ that functions in sexual intercourse by which ejaculation of semen (mixture of sperm and seminal fluid) occurs.

Functional Group and Suffix

The name of an organic compound is determined based on the following steps: Identify the highest-priority functional group, which determines the suffix of the compound name. Determine the number of carbons in the parent chain (ie, the longest continuous carbon chain containing the highest-priority functional group). Number the chain to give the lowest number possible to the highest-priority functional group. All other lower-priority functional groups are named as substituents and listed alphabetically at the beginning of the compound name. The number in front of each substituent name indicates its position in the parent chain (ie, the carbon atom to which the substituent is attached).

Efferent Pathway

The neural process of receiving and acting on sensory information in a reflex arc proceeds through the following steps: An environmental event or disturbance (stimulus) is detected by sensory receptors, which are specialized nerve endings located throughout the body that recognize and respond to highly specific types of stimuli (eg, chemical, light, pressure, vibration). The activated sensory neuron sends an afferent sensory signal (in the form of an electrical impulse) toward the spine, where the signal is transmitted to an interneuron or effector neuron. (Note: Afferent information approachesthe central nervous system [CNS].) As components of the CNS, interneurons in the brain and spinal cord act as integration centers that process and consolidate diverse sensory and CNS input from multiple locations. As such, interneurons can relay sensory information to the brain as well as integrate signals from the brain into the reflex response. However, because interneurons also transmit the signal directly to the effector neuron (and because interneurons are not present in every reflex arc), input from the brain is not necessary for the completion of the reflex. The effector neuron generates and sends an efferent signal that travels toward the target organ (typically a muscle or gland). (Note: Efferent information exits the CNS.) The effector (target) organ generates the desired response to the stimulus.

sense vs antisense strand

The noncoding (antisense or template) DNA strand provides the genetic information necessary for transcription of a new mRNA molecule by RNA polymerase II. Because the newly generated mRNA transcript is synthesized through base pairing with the noncoding strand, the nucleotide sequence of the mRNA strand is complementary to that of the noncoding strand, and its directionality is also reversed. In other words, the sequence of the noncoding strand read in the 5′ to 3′ direction is complementary to the sequence of the mRNA transcript read in the 3′ to 5′ direction. Note that RNA molecules contain uracil (U) nucleotides in place of thymine (T) nucleotides, which are found only in DNA. The coding (sense) strand is the DNA strand that complements the noncoding DNA strand. Accordingly, the coding strand has the same sequence and directionality as the new synthesized mRNA transcript with one exception: The mRNA transcript has U rather than T nucleotides. The only option that matches the direction and sequence (with T in place of U) of the given mRNA sequence is

The pituitary gland

The pituitary gland is a small structure that sits inside a bony cavity below the hypothalamus at the base of the brain. It is attached to the hypothalamus via the pituitary stalk and can be divided into two separate lobes: The anterior lobe is made up of glandular tissue containing different cell types that synthesize and secrete follicle-stimulating hormone (FSH), luteinizing hormone (LH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), growth hormone (GH), β-endorphins, and prolactin. The synthesis and secretion of hormones from the anterior pituitary is controlled primarily by neurohormones released from hypothalamic neurons. These regulatory neurohormones are secreted into the hypophyseal portal system, a venous network of small blood vessels that enables small quantities of hormones secreted from the hypothalamus to directly reach the anterior pituitary without being diluted in the circulation. The posterior lobe, made up of axonal projections from the hypothalamus, stores and secretes the hormones oxytocin and vasopressin (also called antidiuretic hormone [ADH]). Posterior pituitary hormones are synthesized in hypothalamic neurons and then transported down the axon to the axon terminals in the posterior pituitary, where they are stored. The secretion of stored hormones from the posterior pituitary is mediated by action potentials that cause exocytosis of neurosecretory vesicles.

post pituitary

The posterior lobe of the pituitary gland contains the axonal processes of hypothalamic neurons. The hormones antidiuretic hormone (ADH) and oxytocin are synthesized by these specialized neurons and stored within their axon terminals, which form junctions with systemic blood vessels. As a result, the firing of hypothalamic neurons results in the release of ADH or oxytocin into the systemic circulation.

Enzymatic reaction rate can be expressed as a fraction of Vmax and is directly related to substrate concentration, which can be expressed as a multiple of Km. Inhibitors that work well at low substrate concentrations ([S] << Km) might not work as well at higher concentrations, and vice versa.

The rate of an enzymatically catalyzed reaction is dependent on substrate concentration, which can be expressed in terms of multiples ofKm. The reaction velocity for any enzymatic reaction can be expressed as a percentage ofVmaxsuch that if substrate concentration is equal to nKm, the reaction runs at n/(n+1) Vmax. For example, when substrate concentration is equal to Km, the reaction rate is 1/(1+1) Vmax = ½Vmax. When substrate concentration is equal to 2Km, the reaction rate is 2/(2+1) Vmax = (2/3)Vmax, and so on. Varying the substrate concentrations alters the reaction velocity by changing the concentration of the enzyme-substrate complex.

EXPAIN RAS,Aldosterone and ADH

The renin-angiotensin system (RAS) is a multiorgan molecular cascade activated when BP (or blood volume) falls. A drop in BP causes the juxtaglomerular cells in the kidney to release renin, an enzyme that cleaves the plasma protein angiotensinogen to form angiotensin I. Angiotensin-converting enzyme then cleaves angiotensin I to form angiotensin II. Angiotensin II ultimately raises BP by inducing both the release of aldosterone from the adrenal cortex (increasing BP by increasing blood volume through water retention) and the constriction of arterioles (increasing BP without changing blood volume). Aldosterone is released in response to RAS activation or to an increased serum level of K+. Aldosterone acts on the distal tubules and collecting ducts of nephrons to promote the reabsorption of Na+ and the secretion of K+. Increased reabsorption of Na+ increases the osmolarity, or solute concentration, of the renal interstitial fluid. Elevated osmolarity promotes water reabsorption, which ultimately causes blood volume and BP to increase. ADH is released by the posterior pituitary when BP falls or when blood osmolarity rises. ADH promotes water reabsorption by increasing the permeability of the distal tubule and collecting duct to water. It also induces vasoconstriction, the narrowing of blood vessels. Both of these effects increase BP.

pyloric sphincter

The segments of the small intestine include the duodenum, jejunum, and ileum. The pyloric sphincter is a muscular ring located at the junction of the stomach and the duodenum; this sphincter controls the flow of chyme, or partially digested food, from the stomach into the duodenum

Glucose is a key energy source for many tissues in the human body. The serum level of glucose is tightly regulated through the actions of the hormones insulin, glucagon, epinephrine, norepinephrine, and the glucocorticoids. Explain more

The serum level of glucose is also subject to homeostatic control primarily through the actions of hormones. When blood glucose levels are low (eg, during periods of fasting), the hormone glucagon is secreted from the alpha cells of the pancreas, and the autonomic nervous system promotes the release of epinephrine and norepinephrine by the adrenal medulla. Glucagon is a peptide hormone that promotes gluceoneogenesis (the synthesis of glucose from other molecules) and glycogenolysis (the breakdown of glycogen into glucose). Epinephrine and norepinephrine also promote glycogenolysis. Therefore, the overall effect of glucagon, epinephrine, and norepinephrine is to promote the synthesis of glucose and its release into the systemic circulation, thereby correcting the low serum level of glucose.

Sebacic acid (HOOC−(CH2)8−COOH) is a naturally occurring dicarboxylic acid found in urine. A 200 mg sample of sebacic acid crystals would have the highest solubility in a dilute aqueous solution of: A. a weak acid. (19%) B. a weak base. (58%) C. a neutral ionic salt. (7%) D. distilled water. (13%)

The structure of sebacic acid has polar covalent C=O, C-O, and O-H bonds that readily interact with water via dipole-dipole and hydrogen bonding interactions. Nevertheless, the solubility of sebacic acid in water is still very limited due to the nonpolar C-C and C-H bonds of the central hydrocarbon chain, which is hydrophobic and repels water molecules. Because bases neutralize acids, the solubility of sebacic acid can be increased by adding a base to deprotonate the carboxylic acid groups. The resulting acid-base neutralization reaction converts the carboxylic acid groups into ionic carboxylate salts, which have much higher aqueous solubility because they are charged and highly polar. The added charge increases the attraction to water and overcomes the repulsion from the hydrocarbon chain. Therefore, a sample of sebacic acid crystals would have the highest solubility in a dilute basic solution. Sebacic acid is a weak acid, and adding another weak acid will not increase solubility because two weak acids will not neutralize or ionize each other.

Two forms of reproductive isolation

There are two forms of reproductive isolation: Prezygotic reproductive isolation occurs when fertilization is prevented between the sperm of a male from one species and the egg of a female from another species (ie, occurs before zygote formation). Postzygotic reproductive isolation occurs when fertilization takes place but resulting offspring are inviable or infertile (ie, occurs after zygote formation).

separation of enantiomers

Therefore, separation of enantiomers relies on changing the physical properties of the molecules. The separation of enantiomers, such as those in the racemic mixture of albuterol, requires the addition of a resolving agent (a chiral molecule). When a resolving agent is added to a racemic mixture, it reacts with each enantiomer, forming a covalent bond or an ionic salt. Because the resolving agent is chiral, it incorporates a new chiral center into each enantiomer, creating a pair of diastereomers. Diastereomers can be separated from each other because, unlike enantiomers, they have different physical properties. Once the diastereomers are separated, the resolving agent is removed, yielding the original molecules as single enantiomers.

Distinct genes within an organism that have high sequence identity are evolutionary related, likely having a common origin. Where do these genes normally arise?

They generally arise by gene duplication and, over time, can mutate and fulfill distinct roles within an organism. Genes with similar sequences are considered evolutionarily related. In other words, they are believed to have a common origin in a single gene from an ancestor organism. During the process of molecular evolution, portions of a chromosome can be duplicated by mechanisms such as unequal crossing over. Over time, duplicate genes can undergo mutations, causing them to have similar but not identical sequences. These differences allow the genes to carry out distinct roles at various times in an organism's life cycle. The question states that some organisms have multiple genes with highly similar sequences. These similar genes most likely arose by gene duplication

tight junctions

Tight junctions are cell-cell junctions that prevent water and solutes from diffusing between cells and across the epithelial cell layer. These junctions form a watertight seal that fully encircles the apical end of every cell in the basal epithelial sheet. Tight junctions serve as a barrier and separate tissue space; they are found in a number of tissues, including skin, gastrointestinal tract, and testis.

totipotent, pluripotent, multipotent

Totipotent stem cells are the least specialized cells and can give rise to both placental and fetal cells. Pluripotent stem cells can give rise to only fetal cells (ie, all cell lineages from the three germ layers). Multipotent cells are able to differentiate only into the specialized cells of certain tissues; these cells are also found in adults. totipotent cells can differentiate into any cell type from either an embryonic or extraembryonic (placental) lineage Pluripotent cells can give rise to any of the three primary germ layers found in the embryo but not the cells found in placental structures multipotent because they can differentiate into cells with many specialized functions but are limited in that they are "committed" to a specific lineage

Transcription factors

Transcription factors are proteins that can alter gene expression by binding DNA near gene promoter regions to either increase or decrease the transcription of a target gene. Like all proteins, transcription factors are translated in the cytoplasm and must enter the nucleus (where DNA is stored) to influence gene expression. Transcription factors rely on their nuclear localization sequence to gain entrance to the nucleus. The nuclear localization sequence is composed of amino acids and functions as a nuclear import tag that is recognized and bound by nuclear import proteins, which facilitate the transport of transcription factors into the nucleus.

Transcription

Transcription is the process in which the nucleotide sequence of a DNA region is used as a template to synthesize a new RNA strand. Messenger RNA (mRNA) is the type of RNA molecule produced for the transcription of protein-expressing genes. Transcription begins with the binding of transcription factors and RNA polymerase II to a specific AT-rich sequence (TATA box) in the promoter region of double-stranded DNA. RNA polymerase II processes the noncoding DNA strand in a 3′ to 5′ direction until a termination sequence is recognized. As the enzyme travels down the DNA strand, it unravels the DNA double helix and relies on the complementary pairing of bases to catalyze the synthesis of a pre-mRNA strand, which grows in the 5′ to 3′ direction. The pre-mRNA molecule generally undergoes the following modifications to be converted into mature mRNA: A 7-methylguanosine (5′ cap) is added to the 5′ end of pre-mRNA as the nascent transcript is being generated. This 5′ cap is later recognized by the ribosome during translation and prevents the degradation of mRNA in the cytoplasm A chain of adenine nucleotides known as the poly-A tail is added to the 3′ end of the mRNA. This poly-A tail functions to prevent the mRNA from being degraded and also facilitates the export of the mature mRNA from the nucleus to the cytoplasm In pre-mRNA, there are non-coding (introns) and coding regions (exons) located between two untranslated regions (sequences that regulate translation but do not code for amino acids). The noncoding regions (introns) are excised from the pre-mRNA molecule, and the remaining untranslated and coding regions are joined via splicing

Translation

Translation, the energy-requiring process by which ribosomes (with E, P, and A sites) make proteins by reading mRNA, occurs in eukaryotes in the following stages: Initiation: The small 40S ribosomal subunit binds the mRNA 5′ cap and scans the mRNA for a start codon (5′-AUG-3′), which codes for methionine. A transfer RNA (tRNA) molecule "charged" with methionine base pairs with the corresponding AUG codon on mRNA Subsequently, the 60S subunit is recruited and binds the initiator tRNA at the P site, marking the formation of the translation complex. Elongation: The ribosome adds amino acids to the polypeptide chain by reading each mRNA codon in a 5′ to 3′ direction. During each elongation step, a new charged tRNA (ie, a tRNA with an ester bond to an amino acid) enters the A site. The ribosome catalyzes formation of a peptide bond between the C-terminus of the growing P site peptide and the free N-terminus of the A site aminoacyl tRNA, transferring the growing polypeptide chain from the P site to the A site. The ribosome then moves, shifting the newly empty tRNA from the P site to the E site, and the peptidyl-tRNA from the A site to the P site. The E site tRNA is ejected, and a new tRNA enters the A site. Termination: The polypeptide is released from ribosomes when a stop codon (UAA, UAG, or UGA) is detected in the mRNA at the A site, indicating the end of translation. Release factors induce peptidyl transferase to cleave the ester bond between the polypeptide and the final tRNA, causing disassociation of the translation complex.

In the electron transport chain, ubiquinone receives two electrons from NADH, which reduces the carbonyl carbons to hydroxyl groups and forms an aromatic ring, yielding ubiquinol.

Ubiquinone is the fully oxidized form of coenzyme Q, which participates in the electron transport chain in the mitochondrial membrane. The two electrons that ubiquinone receives from NADH reduce the two carbonyls (C=O) in ubiquinone to hydroxyl (-OH) groups. When ubiquinone gains electrons, the number of carbon-heteroatom bonds on each carbonyl carbon decreases from two to one. Electrons are also distributed to the six-membered ring, making it aromatic. Therefore, the structure of ubiquinol contains two hydroxyl groups on an aromatic ring.

Bile and Digestions

Upon meal ingestion, food traverses the mouth and esophagus to enter the stomach, where it is further digested by gastric acid and enzymes to form an acidic, semifluid mixture known as chyme. Chyme then leaves the stomach and enters the duodenum, the first segment of the small intestine. In the duodenum, the presence of meal-derived fats within chyme and the acidity of chyme itself stimulate bile release from both the liver and the gallbladder. Bile secretion into the duodenum promotes the neutralization of chyme and the physical digestion of fats (ie, emulsification). In addition, the chemical digestion of fats in the small intestine is carried out by lipases. Fat digestion products (free fatty acids and monoglycerides) are ultimately absorbed into the body via the microvilli of small intestine epithelial cells.

Female Reproductive Anatomy

Vagina: The sexual organ through which sperm enters the uterus. Endometrial implants within the vagina may impair the passage of sperm and decrease the likelihood that an ovulated oocyte will be fertilized Ovaries: The female gonads that produce gametes (oocytes) and secrete female sex hormones. Endometrial implants attached to the ovary may cause infertility by impairing follicular maturation or ovulation, the release of an oocyte (egg cell) (Choice Fallopian tubes: Duct structures lined with motile cilia that transfer the ovulated oocyte from the abdominal cavity toward the uterus; they are also the primary site of fertilization. Endometrial implants that block or impair the function of the fallopian tubes would prevent a fertilized oocyte from reaching the uterus for implantation Cervix: The barrier separating the vagina and uterus. Endometrial implants that block the cervical canal may impair the passage of sperm and decrease the likelihood of fertilization.

endoskeleton vs exoskeleton

Vertebrates are a group of organisms that have an internal skeleton (endoskeleton) with a bony vertebral column that surrounds the spinal cord and provides points of attachments for other bones and muscles. The endoskeleton provides an internal support structure (scaffold) that allows for movement and protects the internal organs. The vertebrate endoskeleton is composed primarily of bone but also contains cartilage in areas where flexible skeletal tissue is necessary. As a type of connective tissue, bone comprises organic and inorganic materials along with the various cell types (eg, osteoblasts, osteoclasts, osteocytes) involved in bone remodeling. In this scenario, the similarities between the bones of humans and other vertebrates must be compared. Accordingly, the bones of all vertebrate animals form an endoskeleton that provides a scaffold for soft tissues (eg, internal organs, skeletal muscle).

Viroid structure and function

Viroids are subviral infectious particles that each consist of a short circular single strand of RNA. Due to this structure, viroids have regions where the RNA binds with itself (ie, self-complementarity), creating some double-stranded areas of the circular genome. The RNA composing viroids does not generally code for protein, and, unlike viruses, viroids lack protein coats (ie, capsids). When infecting cells, viroids can bind host cellular RNA sequences, resulting in gene silencing that prevents synthesis of necessary proteins. Most known viroids infect plants; however, the pathogen causing hepatitis D is an example of a viroid capable of infecting humans. Viroid replication within a host cell is not well understood. It is thought to be similar to replication displayed by RNA viruses in some cases, while in others the viroid appears to cause the host cell's RNA polymerase to read RNA templates.

Why can water act as a good solvent

Water readily dissolves many polar and ionic compounds because it is able to interact well with them through electrostatic interactions (ie, hydrogen bonding and ion-dipole interactions). Several important characteristics contribute to water's ability to participate in these interactions, including the following: Because oxygen is more electronegative than hydrogen, the bonding electron pairs are more tightly drawn to oxygen. This property results in the oxygen atom having a partial negative charge whereas the hydrogen atoms have a partial positive charge, allowing interactions with other charged molecules The bent geometry of water contributes to its polarity by grouping positive charges at one end of the molecule and negative charges at the other. The charged regions of a water molecule are attracted to opposite charges on other polar compounds Water's small size allows efficient formation of a hydration shell around solutes. This process acts to evenly distribute and isolate solute particles

Western blot analysis

Western blot analysis is a technique used to detect the presence of a specific protein and compare its relative abundance in one set of conditions to that obtained under other conditions. It is performed in the following steps: Samples containing the protein of interest are loaded onto a gel and subjected to electrophoresis, causing the protein to migrate through the gel Proteins in the gel are transferred to a protein-binding membrane such as nitrocellulose or polyvinylidene fluoride (PVDF), where they become immobilized . Transfer is usually carried out by electrophoresis. The portions of the membrane to which protein was not transferred are blocked by protein-rich mixtures such as bovine serum albumin (BSA) or low-fat milk. This step prevents antibodies, which are themselves proteins, from nonspecifically binding to the nitrocellulose in the next step The membrane is incubated with antibodies that specifically bind the protein of interest. These antibodies may be labeled with a marker and detected directly, but more commonly they are subjected to a labeled secondary antibody that specifically binds the first (primary) antibody. Use of secondary antibodies helps improve detection. Antibodies are detected by techniques such as fluorescence or chemiluminescence.

Fluid & lipid transport through the lymphatic system

When blood flows through capillaries, some fluid containing plasma proteins leaks out of the blood vessels and into the interstitial fluid. The interstitial fluid fills the space between blood vessels and surrounding cells. Leaked excess fluid from the capillaries, now also known as interstitial fluid, must be returned to the bloodstream to maintain the proper blood volume and protein concentration. To reenter the bloodstream, the fluid must first pass from the interstitial space and enter a network of vessels and nodes known as the lymphatic system. Once in the lymphatic system, this fluid is now known as lymph and is ultimately drained into two large veins near the heart. In addition, the lymphatic system also collects large lipid droplets absorbed by the small intestine. Certain lipids digested in the small intestine are absorbed by intestinal epithelial cells and packaged into large droplets. However, their large size prevents them from crossing directly into the capillaries surrounding intestinal cells. Instead, these lipid droplets are transported through the lymphatic system and into the bloodstream as follows: Lipid droplets are released from the epithelial cells into the interstitial fluid. Lymph capillaries collect lipid droplets from the interstitial fluid. Lymph containing the lipid droplets then flows from the capillaries into increasingly larger lymph vessels. Lymph is then transported into a large tubule structure called a lymph duct, which drains into a large vein near the heart. As a result, the lipid droplets within the lymph enter the bloodstream and circulate throughout the body

Thermoregulation, the maintenance of body temperature within the normal physiological range, is a major homeostatic function of skin. Thermoregulatory centers in the hypothalamus monitor body temperature by processing information from internal and surface (skin) thermoreceptors. When a significant change in body temperature is detected, the hypothalamic center coordinates the physiological responses necessary to reset the temperature back within the normal range. explain

When body temperature is above normal (as would occur during HA exercise), the following processes cool the body (ie, decrease body temperature): Vasodilation (widening) of skin arterioles increases blood flow to skin capillaries and maximizes heat loss through the skin. This occurs because blood, which is warmed in the body core, transfers heat to the environment when it passes through skin capillaries. Vasodilation occurs when the smooth muscle surrounding the blood vessels relaxes. Sweat, a hypotonic solution, is secreted onto the skin surface by sweat (sudoriferous) glands. Heat loss and subsequent cooling occur due to the evaporation of the water in the sweat, an endothermic process that absorbs heat from the body. When body temperature is below normal, the following processes warm the body (ie, increase body temperature): Vasoconstriction (narrowing) of skin arterioles minimizes heat loss by diverting warm blood away from skin capillaries and toward blood vessels in the interior of the body. Vasoconstriction occurs when the smooth muscle surrounding the blood vessels contracts (Choice A). Shivering generates heat through rhythmic involuntary contractions of skeletal muscle.

blood clot formation

When the blood vessel wall is damaged, platelets (non-nucleated cellular fragments generated from large bone marrow cells called megakaryocytes) adhere to the exposed connective tissue and form a plug at the site of injury. This plug is later stabilized as a clot by fibrin, an insoluble protein that polymerizes into long fibers that cross-link like a net over the damaged area. Platelets and fibrin, not endothelial cells, bind sites of vascular damage to form clot

sliding filament model

When the muscle fiber is at rest, the myosin head is in its high-energy conformation (upright and bound to ADP and Pi), and the actin filaments are bound by the regulatory proteins tropomyosin and troponin. Tropomyosin is an elongated protein that wraps around the actin filament to block myosin-binding sites on this thin filament. Troponin is a small protein complex associated with tropomyosin. Following a depolarizing stimulus by a motor neuron, Ca2+ ions are released from the sarcoplasmic reticulum into the cytosol. The abundant cytosolic Ca2+ ions bind troponin, causing a conformational change that ultimately pulls on tropomyosin and exposes the myosin binding sites on the actin filaments When the active sites are exposed, the myosin head is able to bind strongly to the actin filament, forming a cross-bridge. The dissociation of Pi initiates the power stroke, which is the actual pivot of the actin-bound myosin head that drags the actin filament toward the center of the sarcomere. This directly results in shortening of the sarcomere. The release of ADP from the myosin head occurs at the end of the power stroke. The myosin head is now in its low-energy conformation. A new ATP molecule binds the myosin head and the cross-bridge disassembles Hydrolysis of the ATP molecule allows the myosin head to shift back into its upright, high-energy conformation in preparation for a new cycle of contraction The cycle of cross-bridge formation and disassembly continues until motor neuron signaling ceases, and Ca2+ is sequestered back into the sarcoplasmic reticulum.

genetic leakage (gene flow)

When two individuals from two different parental species reproduce, their offspring are known as hybrid organisms. If these hybrid offspring successfully mate with members of either parental species, genetic leakage may occur. Genetic leakage is generally defined as the transfer of genetic information (ie, genes) between different species. For example, genetic leakage occurs when an individual from a hybrid species and another from the parental species that formed the hybrid mate and produce viable offspring. When this mating takes place, offspring inherit genes from the parental species and from the hybrid species, which contains genes from two different parental species. If this type of mating continues over time, gene flow will occur from the hybrid species to the parental species with which it breeds because hybrid genes will continue to be transferred to the parental specie

Constructive/destructive interference

When two waves meet at the same point, they overlap with one another and cause wave interference. Pure constructive interference occurs when the peaks and troughs of the two waves overlap exactly, meaning the phase difference between the waves is 0°. This corresponds to a path length difference Δd between the two waves of zero or an integer multiple of the wavelength λ: ∆d=0,λ,2λ,3λ,...∆d=0,λ,2λ,3λ,... When the peaks of one wave overlap exactly with the troughs of the other wave, the phase difference between the waves is 180° and pure destructive interference occurs. This happens when the difference in path length is half the wavelength or an odd multiple of half the wavelength: ∆d=λ/2,3λ/2,... In this question, the wavelength is 600 nm and destructive interference occurs when the path length difference is 300 nm, 900 nm, 1,500 nm, and so on. When the difference in the path lengths is 300 nm, the sum of the two waves yields a zero signal consistent with destructive interference.

Lewis Acid and Lewis Base in Coordination Complexes

Within coordination complexes, a ligand acts as a Lewis base, and the metal center acts as a Lewis acid. Ligand structures that can form more than one coordinate bond by donating more than one pair of electrons have more than one site that can function as a Lewis base.

Does Primary structure determine the tertiary structure?

Yes! The three-dimensional folded form of a protein, including secondary and tertiary structure, is entirely determined by primary structure (amino acid sequence). Therefore, proteins with similar amino acid sequences often fold similarly, and those with similar folds most likely have similar amino acid sequences. Proteins with different sequences are likely to adopt distinct folds. Domains within a protein behave as individual units and typically fold independently from each other.

Hyline Cartilag is the most common type of cartilage is hyaline cartilage, which lines the ends of articulating bones and plays a role in bone development.

extra info: Cartilage is a connective tissue made up of cells that secrete a specialized extracellular matrix called chondrin, which contains collagen fibers, proteoglycans, and water. Cartilage may be classified as hyaline, elastic, or fibrous cartilage depending on its composition. The firm but flexible structure of cartilage is resistant to compression and stretching. Hence, most of the cartilage in the body is found in parts that require cushioning (eg, joint surfaces, spine) and on the articulating surfaces of bone ends. Specifically, hyaline cartilage is the most abundant cartilage type in the body and is found on the ends of long bones as well as in the ribs, nose, trachea, and larynx. Because cartilage lacks nerves (ie, is not innervated) and is avascular (ie, lacks its own blood supply), it must receive nutrients and oxygen via diffusion from surrounding fluids or vascularized areas (Choices A and D). Cartilage also plays a role in certain mechanisms of bone development. The process of endochondral ossification uses hyaline cartilage as a template for bone deposition (Choice B). During fetal development, hyaline cartilage composing the fetal skeleton is replaced by bone (ie, calcification). In children and adolescents, the epiphyseal (growth) plate of long bones is formed from hyaline cartilage and serves as the site of bone lengthening. In contrast, bone formation can also occur via intramembranous ossification, a process in which bone is formed directly from fibrous connective tissue (not hyaline cartilage). Mesenchymal (connective tissue) stem cells within this connective tissue differentiate into osteoblasts and secrete the bone matrix. Ligaments and tendons are important connective tissue structures at joints. Tendons (not hyaline cartilage) tautly anchor muscle to bone. Tendons are strong, fibrous bands of connective tissue that transmit a force generated by contracting muscle to the bone, permitting locomotion (movement). In contrast, ligaments are strong bundles of connective fibers that connect bones to other bones and stabilize and hold structures together.

There are two major types of phospholipids

glycerophospholipids and sphingophospholipids.

Inbreeding results in decreased ______(genetic diversity), reduced fecundity, and reduced fitness. Species that mate with nonrelatives (outbreed) increase their fitness because the introduction of new genetic material results in increased heterozygosity.

heterozygosity

as protons are pumped out of the mitochondrial matrix, the pH of the matrix increases. Consequently, the increased proton pumping associated with increased electron transport chain activity would result in a ----- mitochondrial matrix pH.

higher

A correctly folded protein that contains all cofactors is referred to as the holoprotein whereas those that lack cofactors are called apoproteins.

holoprotein vs apoprotein

vibrational modes are excited by

infrared light

Isotopes are atoms of the same element with a different number of neutrons in the nucleus. Isotopes are designated by their mass number (the sum of the protons and neutrons in the nucleus) either by using the element name hyphenated with its mass number (eg, fluorine-18), or by using a chemical symbol with the mass number given as a preceding superscript (eg, 18F).

isotopes

Genetic drift refers to random genetic changes in allele frequency that are due to chance events (not natural selection). Compared to large populations, small populations are____ susceptible to allele loss via genetic drift.

more

Transport and Activation of Long Chain Fatty Acids in the Mitochondria

ntry into the mitochondrial matrix is tightly regulated by the inner mitochondrial membrane. Crossing the membrane generally requires the aid of transport proteins, which only recognize specific molecules. Some short-chain fatty acids can cross the inner mitochondrial membrane directly, but long-chain fatty acids can only cross the outer mitochondrial membrane. Additionally, long-chain fatty acids are not recognized by any transport proteins; they must be modified or "activated" to enter the matrix. Fatty acid activation and transport includes the following steps: In the cytosol, the enzyme acyl-CoA synthetase catalyzes the reaction of fatty acids with coenzyme A to form acyl-CoA molecules. This reaction is thermodynamically unfavorable and requires ATP hydrolysis to proceed Acyl-CoA molecules then migrate to the intermembrane space, where they can react with carnitine to form acylcarnitine. The transport protein acylcarnitine translocase, located on the inner mitochondrial membrane, recognizes acylcarnitine and carries it into the mitochondrial matrix Acylcarnitine is then converted back to acyl-CoA and carnitine. Acyl-CoA is subsequently digested by β-oxidation, and carnitine is transported out of the matrix where it can pick up and carry a new fatty acid into the mitochondrial matrix.

Innervation of the adrenal medulla by the autonomic nervous system is unique in that the adrenal medulla is ....

only innervated by the sympathetic nervous system. extra note: for a drug to trigger an increased secretion of norepinephrine and epinephrine by the adrenal medulla, the drug must generate effects that mimic the activity of the sympathetic nervous system.

The more positively charged the protein is at physiological pH, the higher its

pI

perineum

perineum is the area between the anus and the scrotum (in males) or vulva (in females).

Oxoloacetate

s an intermediate in the citric acid cycle, gluconeogenesis, and transport of acetyl-CoAfrom the mitochondria into the cytosol for fatty acid synthesis, it is not involved in transport of fatty acids from the cytosol into the mitochondria.

Combustion reactions involve

the burning of a fuel (often a hydrocarbon, an alcohol, or another flammable organic compound) in the presence of oxygen, often from the air. When the supply of oxygen is plentiful, complete combustion occurs to form carbon dioxide (CO2) and water. The reaction of methane (CH4), a hydrocarbon fuel, with oxygen to form CO2 and water is an example of a complete combustion reaction.

Glucose 6-phosphate dehydrogenase (G6PDH)

the enzyme that catalyzes the first step in the oxidative phase of the pentose phosphate pathway; it decarboxylates glucose-6-P to form ribulose-5-P and forms NADPH in the process

tertiary structure is primarily stabilized by ------ nteractions between -----

the tertiary structure of a protein is its three-dimensional, folded form. Tertiary structure is primarily stabilized by noncovalent interactionsbetween side chains, often bringing amino acids that are far apart in the primary structure closer together.

When muscle contraction occurs, the myosin and actin filaments interact. Specifically, myosin heads bind to the actin filaments and slide them toward the central point of the sarcomere. This interaction shortens the sarcomere's total length; however, the length of each actin and myosin filament remains ------ Instead, it is the sliding of the two filament types along one another that causes the sarcomere to shorten.

unchanged.

If two genes are located close together on a chromosome (measured in centimorgans, or map units), they are relatively ______ by a recombination event.

unlikely to be separated

Fatty acid synthesis

Fatty acid synthase carries out the main reactions of fatty acid synthesis and contains an acyl carrier protein (ACP)responsible for transferring acyl intermediates. Acetyl-CoA and malonyl-CoA are activated to acetyl-ACP and malonyl-ACP, which are condensed into acetoacetyl-ACP. Subsequently, acetoacetyl-ACP is reduced, dehydrated, and further reduced to generate butyryl-ACP. The coenzyme NADPH is used for both reductive steps. The reactions are repeated until a 16-carbon fatty acid (palmitate) is formed via addition of two carbon atoms per cycle. Because ACC activity is uninhibited in the presence of AMPK phosphatases, fatty acid synthesis is stimulated and the activity of the acyl carrier protein is increased.

An objects acceleration is equal to the net force exerted on the object divided by the objects mass

Fo

Gas liquid chromatography

Gas liquid chromatography is a technique used to separate compounds based on boiling point, which depends on several factors, including molecular weight and intermolecular forces. A small amount of a liquid mixture is injected into the gas chromatograph, and the compounds are vaporized by heating. The most volatile (lowest boiling) compound will vaporize rapidly, move through the column quickly, and have the shortest retention time. Higher boiling compounds can condense and interact with the liquid stationary phase longer (ie, move more slowly through the column), resulting in longer retention times.

heterochromatin vs. euchromatin

Heterochromatin consists of DNA that is tightly coiled around histone proteins, bound by an ionic interaction between the negatively charged phosphates on the DNA backbone and positively charged lysine residues in the histone. DNA in heterochromatin is not readily accessible to RNA polymerase and so cannot be readily transcribed. Euchromatin forms when histones are modified, often by acetylation of lysine residues. The added acetyl group neutralizes the positive charge on a lysine residue, reducing interactions between histones and DNA. The reduced interactions yield a more open form that is more accessible to RNA polymerase, allowing euchromatin to be more readily transcribed. Heterochromatin is tightly wound DNA characterized by low levels of histone acetylation and high levels of DNA methylation. Genes in these regions are considered silenced because the DNA is so tightly packed that it is inaccessible to the transcription machinery. In contrast, euchromatin is marked by high levels of histone acetylation and low levels of DNA methylation. This makes euchromatin looser and the DNA more accessible to the transcription machinery, allowing gene expression.

When enough energy (transferred as heat) is either absorbed or released by a substance, a phase change can occur. During this process, the temperature of the substance remains constant until the substance has completely transformed from one phase to another. The latent heat is the amount of heat that 1 mole of a substance must absorb or release to undergo a phase change at constant temperature. The latent heat transferred for complimentary phase changes (eg, freezing and melting) is equal in magnitude but opposite in sign (ie, the sign indicates if the heat is absorbed or released). There are two common types of latent heat: What are they?

Latent heat of fusion (ΔHfusion) is the amount of heat a substance must absorb to transition from a solid to a liquid (ie, melting). The opposite process (ie, going from liquid to a solid) releases energy and the latent heat ΔHsolidification of this reverse process is equal to −ΔHfusion. Latent heat of vaporization (ΔHvaporization) is the amount of heat a substance must absorb to transition from a liquid to a gas (ie, boiling). The opposite process (ie, going from gas to a liquid) releases energy, and the latent heat ΔHcondensation for this reverse process is equal to −ΔHvaporization.

London dispersion forces,

London dispersion forces, a type of intermolecular force, occur when two neighboring, nonpolar species induce a temporary distortion of the electron clouds, resulting in weak, momentary dipoles. The strength of the attractive force between the dipoles depends on the size and shape of the species. Larger molecules have larger electron clouds that are more polarizable and yield stronger attractive London forces. Furthermore, the shape of the molecule affects the amount of polarizable orbital "surface area" available to interact with surrounding molecules. The greater the surface-to-surface contact between molecules, the greater the London dispersion forces. Higher London Dispersion forces = higher melting point

Induction

Reactivity of carboxylic acid derivatives with a nucleophile depends on various factors, including inductive effects, steric effects, and leaving group stability. Induction is an electronic property in which electrons are donated through sigma bonds. Electronegative atoms or electron withdrawing substituents pull electrons away from an adjacent atom toward themselves, creating a dipole. The closer the electron withdrawing group to an atom, the greater the inductive effect that atom experiences.

macrophage

The primary function of macrophages, which can either travel the body or remain fixed in a specific tissue, is to degrade pathogens and dead body cells. The degradative function of macrophages is performed via phagocytosis, the process of engulfing solid particles (eg, microbial pathogens) designated for destruction into phagocytic vesicles called phagosomes. Within the cell, phagosomes typically fuse with lysosomes to form phagolysosomes, which enable the degradation of the engulfed particles using specialized enzymes that work at low pH.

Maintenance of Resting Membrane Potential

The unequal concentration of charged ions between the extracellular and intracellular fluid of all living cells results in an electrochemical gradient across the membrane that determines the membrane potential (voltage difference). The resting membrane potential of neurons is due primarily to the high concentration of potassium ions (K+) and the low concentration of sodium ions (Na+) inside the cell compared to the outside. The following mechanisms contribute to maintenance of the resting membrane potential: Protein channels in the cell membrane enable certain ions to move down their concentration gradient across the membrane. For example, in resting neurons, potassium (K+) leak channels help maintain the membrane potential by enabling the passive transport (without using energy) of K+ out of the cell. The membrane is more permeable to K+ than to Na+ (ie, selective permeability) due to the presence of a greater number of K+ leak channels. Therefore, the resting membrane potential of neurons is approximately −70 mV, which is close to the negative equilibrium potential of K+ Active transport pumps embedded in the outer membrane of neurons hydrolyze adenosine triphosphate (ATP) to provide energy to transport molecules against their concentration gradient. For example, sodium-potassium pumps (Na+,K+-ATPase) transport 2 K+ into the cell for every 3 Na+ moved out. This is important for maintaining the unequal concentration of ions across the membrane; without active transport pumps, leakage of ions through the cell membrane would eventually result in equilibration and a membrane potential of 0 mV (Number II).

Acids and nucleoephility

acids can catalyze many reactions by donating protons to a reactant generating an increased positive charge. This creates enhanced electrophiles such as carbocations and increases the stability of leaving groups. Acids generally decrease nucleophilicity of the molecules to which they donate protons.

Anhydrides contain stronger electron withdrawing groups than amides, therefore

anhydrides experience a greater inductive effect and react more readily than amides

Reaction optimization is necessary to

determine under what conditions the desired product really forms while

Stroke volume

is the volume of blood pumped out in a single heartbeat. The SV depends on the change in the volume of the left ventricle before and after the contraction of the heart. The volume of the left ventricle before contraction is the end diastolic volume EDV and the volume after contraction is the end systolic volume ESV, yielding SV = EDV - ESV

Buffer

mixture of a weak acid or base and its corresponding conjugate salt resulting in a system that contains both acidic and basic species that can be protonated or deprotonated over a specific pH range.

Equilibrium Partial Pressure

molar ratio of products to reactants when equilibrium is achieved. Each product or reactant must be raised to the power of its stoichiometric coefficient in the equilibrium expression

basophils

the primary function of basophils, a type of granulocyte, is to release chemical mediators such as histamine that enhance the immune response. Released histamine causes vasodilation and permeability of vessels, which stimulates an inflammatory response by increasing blood flow and the delivery of immune cells (eg, neutrophils and macrophages) at the site of infection. Therefore, during an infection, macrophages function to phagocytose organisms and basophils release histamine.

wave velocity equation

v = fλ v can sometimes be equal to the speed of light c = 3 * 10^8 in certain situations

vacuum distillation

vacuum distillation is performed under reduced pressure, lowering a compounds boiling point relative to its boiling point at atmospheric pressure. Vacuum distillation is ideal for compounds with a boiling point about 150 degrees celcisu to prevent degradation

acceleration

velocity/time

superheating

when a liquid is heated past its boiling point but does not boil; surface tension can prevent bubbles from forming and therefore cause superheating when bulbs try to form, the surface tension can cause an increase in the local vapor pressure that goes beyond the ambient pressure, allowing the liquid to heat past its boiling point

Newtons third law of motion implies that force exists in pairs. Thus..

when an object exerts a force on a second object, the second object exerts an equal and opposite force back on the first object

Buffering range

when the buffer can neutralize added hydronoium or hydroxide ions and therefore resit changes in pH