BIO/BIOCHEM

What would be the overall charge on the oligopeptide DDKYEHHQ at physiological pH? At physiological pH (7.4), what charge would be observed on the tripeptide KHR True or false: Under physiological conditions, all basic amino acids will be predominantly positively charged. At physiological pH, what will be the charge on the dipeptide DE?

-2 +2. This tripeptide is made up of the three basic amino acids: lysine (K), histidine (H), and arginine (R). However, we must keep in mind that histidine is predominantly neutral at physiological pH, while the other two are positively charged. Therefore, we would predict the overall charge on this tripeptide to be +2 This statement is false. The basic amino acids lysine and arginine are indeed predominantly positively charged at physiological pH, but this is not true of histidine. Histidine is predominantly neutral at physiological pH. Aspartic acid (Asp, D) and glutamic acid (Glu, E) are the two acidic amino acids, and are both negatively charged at physiological pH. Therefore, a dipeptide composed of these two amino acids will have an overall charge of -2.

9% of individuals within a population of butterflies are resistant to milkweed toxins, a trait which arises from a recessive allele. If these butterflies reproduce exclusively within their population, genetic mutations do not occur, and natural selection does not play a role, what is the predicted frequency of the recessive allele after 10 generations? .0081 0.3 0.42 0.7

0.3 Use the HW equations to solve (p+q=1 and p2+2pq+q2=1): 1.If 9% of individuals have the recessive phenotype, then the homozygous recessive genotype frequency is 0.09. This means that q2 = 0.09. 2. Taking the square root of this value gives q = 0.3, which is the population's recessive allele frequency. Note that the allele frequencies should remain the same regardless of how many generations have passed as the population is not evolving.

Which of the following scenarios are examples of positive feedback? Select all that apply. Sodium ions leak through sodium channels on the membrane of a nerve cell axon arrest causing a change in membrane potential that triggers opening of additional sodium channels. Phosphorylation of a map kinase stimulates autophosphorylation which amplifies activity of the map kinase allowing it to phosphorylate several downstream targets

1 Positive feedback occurs when a downstream product of a pathway activates the pathway at an upstream point. In this case, sodium ions moving out of the axon are the downstream product. Since they trigger sodium channels to open, which results in more sodium ions moving across the membrane, the response gets amplified very quickly. This is an example of positive feedback.

In eukaryotic cells, DNA replication takes place in the: 1 nucleus 2 cytosol 3 mitochondria

1 & 3 only Both the nucleus and the mitochondria contain their own DNA genomes. In eukaryotes, mitochondrial and nuclear DNA replication occurs independently of each other and within their respective organelles.

Select all of the following events that do not occur during the same phase of meiosis one as a crossing over: Chromosomes move to opposite poles of the cell. Microfilaments begin to form the spindle apparatus is the emerge from centrosomes. All 46 chromosomes in 23 homologous pairs along with the replicated copies condense. The nuclear envelope begins to disintegrate

1 2 Chromosomes do not move to opposite poles until anaphase. Microtubules, not microfilaments, comprise the spindle apparatus.

Select all the following which are true of both the Strecker and Gabriel synthesis reactions. They can produce nonessential amino acids they involve an aldehyde is it starting reacting. Certain steps in the synthetic sequence can be catalyzed under acidic conditions. They can occur naturally in living organisms.

1 3

Which of the following statements about enzymes is/are true? Select all that apply. Proteins that catalyze reactions are enzymes. An enzyme reduces the activation energy of the forward reaction while leaving the reverse reaction unchanged. Enzymes are not consumed during the catalysis of a reaction. And enzymes activity is heavily dependent on pH and temperature.

1 3 4 not 2 bc An enzyme functions to lower the activation energy of a reaction. However, it does not do so only for the forward reaction; it necessarily reduces the reverse activation energy as well.

In semiconservative replication: One strain of each daughter molecules from the parent molecule, well the other strand in each daughter molecule is newly synthesized. The strands of both daughter molecules were previously present in a parent molecule

1 DNA replication is semiconservative. In replication, the parent molecule's double helix unwinds, and each strand acts as a template for a new strand. Therefore, DNA replication results in two daughter molecules each comprised of one parent strand and one new strand

Magnesium is an important cofactor for many biological reactions. One such reaction is the phosphorylation of glucose to form glucose-6-phosphate. Which statement is the most likely mechanism of action for magnesium? magnesium helps stabilize the phosphate as it is transferred to glucose magnesium binds outside of the active site to induce a conformational change

1 In an aqueous environment, magnesium will be oxidized and exist in its cationic form Mg2+. The positive charges will interact with and help stabilize the negative charges present on the phosphate molecule during its transfer to glucose.

Which of the following mechanisms can break peptide bonds? Select all that apply. Acid catalyzed hydrolysis. Reducing agents. Changes in pH. Changes in temperature.

1 Peptide bonds are broken through hydrolysis reactions, which can be catalyzed by acid or base in a laboratory setting or facilitated by specialized enzymes inside cells.

Which of the following examples best illustrates the bottleneck effect? A wild side contains all of the Aspen trees on the west side of Forest but the Aspen saw the southern border untouched. Arctic temperatures begin to rise melting ice caps and reducing the global polar bear population, but a small number of polar bears with lower heat sensitivity survive

1 The bottleneck effect occurs when population allele frequencies change in response to a random decrease in population size due to external events, such as natural disasters. This best exemplifies the bottleneck effect as the surviving aspen trees were simply "lucky" in the sense that they had no fitness advantage over trees located at the western edge of the forest. The wildfire did not destroy them because it did not enter the southern region. Any changes in population allele frequencies will be due to random chance alone.

A researcher is investigating the composition of the active site of a particularly important metabolic enzyme, Enzyme Y. Conversion of the enzyme's substrate to product ceases when various drugs, all hydrophobic molecules with similar structures, are administered in in vitro trials. Which of the following statements is most consistent with this information? Either the enzymes active site or allosteric sites are composed largely of hydrophobic residues. The enzymes active site features many as part taken glutamic acid residues. The enzyme contains several allosteric site. The enzyme is covalently modified by the drugs.

1 The enzyme's catalytic activity is inhibited by various hydrophobic drugs. Structural similarity indicates that they interact with the same chemically active site on the enzyme. Since the drug molecules are hydrophobic, the site they interact with is likely hydrophobic as well. However, without further information it is not possible to delineate whether they are interacting with the active site or allosteric site.

Heat shock proteins are chaperone enzymes that facilitate proper folding and assembly of other proteins. Based on the general principles of protein folding, chaperones most likely: Prevent protein aggregation during the folding process. Catalyzed peptide bond synthesis to pull out rapid polypeptide assembly. Remove the free energy barrier that prevents proteins from folding spontaneously. Reduce disulfide bridges to promote subunit aggregation and attachment

1 Unfolded and misfolded proteins tend to aggregate because exposed hydrophobic patches are attracted to each other. This is the most likely mechanism of those listed.

Which of the following are examples of exocytosis? Select all that apply. Release of neurotransmitters into the synaptic cleft Calcium mediated intracellular signaling that results in the activation of protein kinase. Secretion of insulin a peptide hormone A vesicle budding off the plasma membrane into the same cell

1 and 3

Which of the following features distinguish coenzymes from other cofactors? Select all that apply. coenzymes are organic molecules facilitate enzymatic activity contain metal ions cannot function independently

1 only Coenzymes are simply organic cofactors. Regular non-coenzyme cofactors are usually metal ions like iron, calcium, and magnesium.

A graduate student prepares pure samples of five amino acids obtained from human tissue. Four of the five samples rotate plane-polarized light, while one does not. Which of the following statements are reasonable explanations of this observation? Select all that apply. One of the samples contains glycine, which is not a chiral compound One of the samples contains a racemic mixture of L-valine and D-valine One of the samples contains valine, which is not a chiral compound One of the samples contains a racemic mixture of L-glycine and D-glycine One of the samples was contaminated by carbohydrate impurities

1 only bc Glycine is the only non-chiral amino acid, so a pure solution of glycine could not rotate plane-polarized light by definition. Glycine does not possess the four different groups at its alpha carbon required for chirality.

There are many ways to covalently modify proteins. A kinase enzyme facilitates which covalent modification? phosphorylation acetylation hydration methylation

1 phosphorylation Kinases add phosphate groups to proteins, while phosphatases remove them.

Molecular clock analysis could be used to fulfill which of the following research goals? Select all that apply. The evolution of specific viral strains. to estimate the mutation rate of a bacterial gene overtime. T o predict the future speciation events within an isolated population of birds To determine how long ago two different fish species diverged from a common ancestor

1, 4

Which of the following are mechanisms of genetic drift? Select all that apply. Founder effect. Gene flow Disruptive selection Bottleneck effect

1, 4

Osmotic pressure depends on all of the following EXCEPT: solvent concentration number dissolved particles in certain volume of solution temperature ideal gas constant

1. Solvents do not have concentrations. Concentration describes the quanity of dissolved solutes per unit of solvent. While osmosis describes solvent movement across a membrane driven by a solute concentration differential across a membrane, solvent concentration is not a factor of osmotic pressure. not last two bc According to van't Hoff's law, osmotic pressure is directly related to the ideal gas constant.

A geneticist radiolabeled a fragment of dsDNA and allowed it to replicate. After four successive replication cycles, what proportion of the double-stranded DNA molecules contain at least one strand of the original parent material? 1/4 1/8 1/16 1.32

1/8 In semiconservative replication, the parent dsDNA denatures (breaks apart into two single strands). Each denatured strand serves as a template for newly-forming DNA. As a result in the first replication cycle, the two daughter dsDNA molecules each contain a parent DNA strand and a new DNA strand. This repeats with each cycle. After the fourth replication cycle, 16 dsDNA molecules exist. Only two molecules contain an original parent DNA strand. Thus, the correct fraction is 2/16, or 1/8.

In an isolated population of 250 dragonflies, blue wing color is dominant to red wing color. If the frequency of the blue allele is 0.8, how many dragonflies are red? Assume that the population is not evolving 10 50 80 160

10 We need to calculate the number of dragonflies with the homozygous recessive phenotype. The question stem gives us the frequency of the blue allele (p), which we can use to calculate the frequency of the red allele (q) through the formula p + q = 1:0.8 + q = 1q = 0.2 If q = 0.2, then q2 = 0.04, which is the frequency of the homozygous recessive phenotype. To calculate the number of dragonflies with this phenotype, we simply multiply the frequency by the number of dragonflies in the population which yields (0.04)(250) = 10 individuals.

The average molecular weight of an amino acid is roughly 110 g/mol. A novel enzyme is composed of 100 amino acid residues. Approximately how much would a mole of this enzyme weigh?

11 kg The average molecular weight of an amino acid is roughly 110 g/mol. Therefore, an enzyme composed of 100 amino acids would have a molecular weight of 100 × 110 g/mol, or 11,000 g/mol. This corresponds to 11 kg/mol. A quick sum of the molar masses of the atoms in a typical amino acid will yield the rough 110g/mol value needed.

Which of the following is NOT required for primary active transport? Select all that apply. ATP consumption. Movement of molecules against a concentration. Molecules must be able to diffuse back to equip blurry equilibrium ate their concentrations. The presence of some sort of channel

1st and 3rd

Picrophilus torridus is a microbe that lives in extremely acidic conditions, at which the phosphate groups in ATP would be protonated and become neutrally charged. Based on this information, and the knowledge that ATP is its main source of cellular energy, which of the following is the most reasonable prediction we can make about the structure and function of P. torridus? The plasma membrane of P torridus prevents protons from diffusing into the cell P Torridus relies on energy generating pathways that do not involve ATP P t. does not require mechanisms for stabilizing negative charges on intracellular ATP we do not have Internet for enough information to make a reasonable prediction

1st one

Which of the following best describes the concept of passive transport? Moves into the cell with the help of an aquaporin which cost energy to synthesize. Sodium and potassium are passively transported in opposite directions by sodium potassium ATPase. Protons are pumped into the mitochondrial inter-membrane space to establish a concentration gradient

1st. Don't be fooled here by the mention of energy expense. Passive transport requires no energy cost to move molecules across the plasma membrane. Aquaporins use passive transport to move water across the plasma membrane. Additionally, it is expected that any protein channel would require some energy input to synthesize.

Select all of the following which are macromolecules that contain peptide bonds. Amino acids. Polypeptides. Triglycerides.

2

The end product inhibit enzyme one. Intermediate substrate A inhibits enzyme three. Intermediate substrate B activates enzyme one. Intermediate substrate be inhibits enzyme two.

2 3

Catalase is an enzyme found in especially high concentrations in the liver. This molecule catalyzes the conversion of the reactive oxidative species hydrogen peroxide into water and oxygen. Which of the following statements describe(s) what happens in the presence of this enzyme? Select all that apply. The conversion of hydrogen peroxide to water and oxygen gas is made spontaneous. The rate of conversion of hydrogen peroxide to water and oxygen gas is increase. The rate of conversion of water and oxygen gas to hydrogen peroxide is increased. The equilibrium concentrations of water and oxygen gas are increased

2 3 This is correct. By reducing the activation energy, the rates of the forward and reverse reaction increase.

Select each of the following that will always produce a free amino acid. Peptide bond hydrolysis. Strecker synthesis. Gabriel synthesis without malonic esther. Dipeptidase catalysis.

2 4

Which of the following statements are true of disulfide bonds? Select all that apply. Disulfide bonds are a type of ionic bond. Disulfide bonds can be broken by reducing agents. Disulfide bonds form between two methionine residues. Disulfide bonds are an element of quaternary structure.

2 4

The inhibitor increases Vmax. The inhibitor decreases Vmax. The inhibitor increases the substrate concentration needed to reach 1/2 Vmax. The inhibitor decreases the substrate concentration needed to reach 1/2 V max

2 4 The y-intercept of a Lineweaver-Burk plot is equal to 1/Vmax, so an increase in the y-intercept indicates a decrease in Vmax. The x-intercept of a Lineweaver-Burk plot is equal to -1/Km. We can find Km by taking the negative reciprocal of the x-intercept, so a larger negative x-intercept indicates a smaller Km.

How would you expect the osmotic pressure of a 1M solution of dissolved oxygen gas to compare to a 1M solution of dissolved potassium chloride? The solution with dissolve oxygen gas is capable of generating a higher osmotic pressure because dissolved gases can cross semi permeable membrane cytoplasm and membrane. The solution with the dissolve potassium chloride is capable of generating a higher asthmatic pressure due to the higher concentration of solutes. Both solutions will generate roughly the same osmotic pressure if they are both at the same temperature because the solution concentrations are equal. The solution with dissolved oxygen will have a higher osmotic pressure because osmotic pressure depends on the ideal gas constant so only dissolved gases will generate an osmotic pressure

2 A 1M solution of potassium chloride becomes 2M dissolved solutes in solution, as potassium chloride fully dissociates in water into K+ and Cl- ions. Oxygen (which does no dissociate into ions) will be 1M oxygen in water. Therefore, potassium chloride exerts more osmotic pressure.

Type 2 diabetes is often characterized by insulin resistance, in which tissue cells fail to respond to the hormone insulin, causing dangerous increases in levels of circulating glucose. Based on this information, Type 2 diabetes represents the loss of: A positive feedback mechanism. negative feedback mechanism. Feedforward mechanism. Either a positive feedback or a feedforward mechanism

2 Because insulin resistance prevents cellular uptake of glucose from the blood, blood glucose levels must be regulated through negative feedback. In healthy patients, increases in blood glucose prompt the release of insulin, which promotes liver, muscle, and other cells to uptake glucose, thereby decreasing blood glucose levels. Since high blood glucose levels results in a decrease in blood sugar, this is an example of negative feedback.

Convergent evolution and parallel evolution of two species differ with respect to: The type of trait that is acquired by the two species in question. The genetic similarities of the two species in question. Whether the trait in question was about the common ancestor of the two species. What are the two species in question develop similar or different traits

2 Convergent evolution is what occurs when two very different species independently evolve a similar trait, such as a bird and an insect both evolving wings for flight. Parallel evolution happens when two species with a recent common ancestor evolve a similar trait, such as two species of butterflies evolving similar coloration patterns.

Which of the following statements about enzyme structure is correct? Enzymes usually bind noncovalently to substrates but may undergo covalent structural modifications. Enzymes always buying covalently to substrates but do not undergo covalent structural modifications

2 Enzymes interact with substrates primarily through polarity and sterics-based interactions that carefully orient the substrate within the three-dimensional structure of the active site. However, several mechanisms of enzyme regulation do involve covalent modifications, such as phosphorylation, dephosphorylation, and cleavage.

In the context of protein expression, there are two classes of chromatin that exist - heterochromatin and euchromatin. Of the following options, select the most accurate description of euchromatin. DNA loosely wound around histones, allowing for replication. DNA loosely wound around histones, allowing for precise transcription

2 Euchromatin (loosely-wound DNA) has a prominent role in DNA transcription into RNA. Euchromatin's loose conformation allows RNA polymerase and other associated proteins (like transcription factors) to interact with DNA, so that it can transcribe DNA into RNA.

Which of the following is not true of meiosis? The number of chromosomes are halved. It occurs in cells in the uterine endometrium. It involves two cell divisions. Synapsis of homologous chromosomes occurs in prophase 1

2 Meiosis takes place in germ cells (eggs and sperm) only, not in somatic cells, regardless of their location. Germ cells are located in the gonads (ovaries and testes) exclusively.

Mustard gas was a popular toxin in World War I because it caused significant blistering of the skin and lungs, resulting in death. It was later discovered that the mechanism of mustard gas resulted in cell cycle disruption. Which of the following statements best describes the mechanism of action of mustard gas? Mustard gas activate Apple to fix Factice resulting in the death of expose cells. Mustard gas alters nucleotides, significantly inhibiting replication

2 Mustard gas alkylates DNA, which inhibits replication. Though unnecessary to remember for the MCAT®, the logic of inhibiting replication should be enough to conclude the correct answer choice. As the cell cycle needs replicated DNA to proceed, inhibited replication would prevent cells from undergoing the cell cycle.

All of the following statements about prosthetic groups are correct EXCEPT: They are code enzymes. They bind to enzymes allosterically.

2 Prosthetic groups bind tightly to enzymes, so they do not interact allosterically. Allosteric binding is transient and does not occur at the active site.

Which of the following choices best explains why positive cooperativity results in a substrate binding curve with a sigmoidal shape? as the concentration of substrate increases, more active sites on the enzyme become occupied until the enzyme is saturated the rate of substrate binding increases as substrate concentration increases until the enzyme is saturated

2 Substrate binding to a positively cooperative enzyme is slow at first but eventually increases because the binding of initial substrate molecules increases the affinity of other active sites for the substrate. Therefore, the substrate binding curve begins horizontally but quickly becomes ore vertical. It levels out again once the enzyme becomes saturated with substrate.

n addition to the standard representation that is typically shown, peptide bonds have what additional resonance structure? A double bond between the carbonyl carbon and carbonyl oxygen. A double bond between carbonyl carbon and amide oxygen.

2 This is the additional resonance structure that exists, where the double bond between carbon and oxygen shifts to be between carbon and nitrogen.

Which of the following statements are true about genetic drift? Select all that apply It is a type of selective pressure. It causes random changes in allele frequencies. It can lead to loss of genetic diversity. Has a greater effect in small populations.

2,3,4

Select all that apply to complete the following sentence. Histone acetyltransferase... Functions mainly to perform post-transcriptional modification. Catalyzes a transfer of an acetyl group. Increases transcription of DNA associated with the histone in question. Decreases transcription of the DNA associated with a histone in question

2,3. Histone acetyltransferase functions to add acetyl groups to histone proteins, a process that serves as a post-translational modification. This reduces the positive charge held by the basic histone proteins, loosening the DNA-histone conformation and increasing transcriptional activity.

Which of the following solutions has the highest osmolarity? 2.5M NaCl 2M MgCl2 1M CaCO3 0.5 M glucose C6H1206

2. Osmolarity takes into account ALL solute particles. Magnesium chloride dissociates into three ions in solution: two chloride anions and one magnesium cation. The osmolarity will therefore be: 2M MgCl2 x 3 particles/ MgCl2 molecule = 6 osmoles.

Which of the following statements best describes the concept of natural selection? Change in allele frequencies in a population over time. Differential survival and reproduction. And individuals probability of reproductive success. Collection of genes found within a population.

2. not the first. bc Change in allele frequencies over time refers to the concept of evolution.

Which of the following statements is LEAST applicable to endosomes? Zones are bound to the plasma membrane on the intracellular side. Enzymes are responsible for sorting material that was ingested via endocytosis and degrading material the cell does not want to use. Enzymes identify receptors that should be sent back to the plasma membrane. Endosomes are organelles

2nd

How would you expect the osmotic pressure of a 1M solution of dissolved oxygen gas to compare to a 1M solution of dissolved potassium chloride? the solution of dissolved oxygen gas is capable of generating a higher osmotic pressure because dissolved gases can cross semi permeable membranes like the plasma membrane. The solution with a dissolve potassium chloride is capable of generating a higher asthmatic pressure due to the higher concentration of solutes. Both solutions will generate roughly the same as money pressure if they are both at the same temperature

2nd . Dissolution of dissolved oxygen gas is capable of generating a higher osmotic pressure because dissolved gases can cross semi permeable membranes like the plasma membrane. The solution with a dissolve potassium chloride as capable of generating a higher asthmatic pressure due to the higher concentration of solutes. Both solutions will generate roughly the same asthmatic pressure if they are both at the same temperature is a solution concentrations are equal the solution with the dissolved oxygen will have a higher is my pressure because I

Which of the following causative relationships listed below are correct? Select all that apply. Evolution results in fitness. Natural selection results in evolution. Natural selection results in fitness. Fitness results in natural selection

2nd bc Natural selection refers to the differential survival and reproduction of individuals based on whether they have favorable traits. This is the mechanism through which evolution takes place. not third one bc Natural selection refers to differential survival and reproduction of individuals with different traits. The fitness of a trait tells us how likely it is to remain within a population over time. There is not a causative relationship between these terms.

Beta-oxidation is a process through which the body generates energy from fatty acids. Which fact about this process should be the highest priority when studying? Transport of fatty acids into the mitochondrial matrix requires the carnitines shuttle. The acetyl CoA produced from this pathway is shunted into the citric acid cycle. The final step of beta oxidization beta oxidation for odd-numbered fatty acids resulting propionyl CoA as well as acetyl CoA. Specialized enzymes exist for handing the double handling the double bonds in unsaturated fatty acids.

2nd bc Understanding the products of a pathway and what happens to them is high-priority knowledge that both can be used to deduce the answer to questions directly and to organize your understanding of the smaller-scale details of the process. not the rest bc "While this is a relevant detail, it is a lower priority than understanding the basic products and purpose of a pathway."

In cells, protein folding takes place in an aqueous environment. If protein folding were instead to take place in hexane, a nonpolar solvent, which outcome would be LEAST likely? the protein would not be able to carry out the same functions nonpolar amino acids would be more likely to be located in the core of the protein, shielded from solvent interactions polar and charged amino acids would be more likely to be buried in the core of the protein, shielded from solvent interactions nonpolar amino acids would be more likely to be located on the surface of the protein, exposed to the solvent

2nd. Nonpolar amino acids would preferentially associate with the nonpolar solvent, while polar and charged amino acids would tend to cluster away from the solvent. This would result in a tendency for nonpolar amino acids to be at the surface of the protein, facing the solvent, while the polar and charged amino acids would cluster in the core of the protein, away from the solvent. This is the opposite of what is described in choice B, making choice B the correct answer for this "least" question.

Which of the following solutions has the highest osmolarity? 2.5M NaCl 2M MgCl2 1M CaCO3 0.5M glucose

2nd. Osmolarity takes into account ALL solute particles. Magnesium chloride dissociates into three ions in solution: two chloride anions and one magnesium cation. The osmolarity will therefore be: 2M MgCl2 x 3 particles/ MgCl2 molecule = 6 osmoles.

From an evolutionary perspective, which of the following organisms is best described as 'fit'? An organism that can survive in extreme environmental conditions. An organism that integrates optimal into its ecosystem. An organism that generates a large number of progeny

3

What is the major synthetic enzyme of bacterial DNA replication? DNA polymerase... 1 2 3

3

Which of the following enzymes most likely catalyzes the formation of a dipeptide from two amino acids? Alanine racemates. valine - tRNA ligase Glutamate - cysteine ligase. Dipeptidyl - peptidase

3 Even though these enzymes may be completely unfamiliar, the correct answer can be deduced from a knowledge of enzyme nomenclature. Ligases are enzymes that form covalent bonds between two molecules, which is what the question describes. The name of glutamate-cysteine ligase indicates that it catalyzes the formation of a covalent bond between glutamate and cysteine, which corresponds precisely to what the question stem describes.

DNA is a polymer of: Nucleoside triphosphates. Nitrogenous bases. Nucleoside monophosphate.

3 Nucleic acids are nucleotide polymers, which comprise of nucleosides (a nitrogenous base, such as A, C, G, T, or U, and a five-carbon sugar) and an attached phosphate group. The nucleoside and the single attached phosphate group make DNA a nucleoside monophosphate polymer.

Protein folding is most dependent upon: Stearic repulsion between bulky amino acid side chains. Hydrogen bonding between backbone atoms. Interactions of nonpolar amino acids with solvent molecules. Peptide bond formation between adjacent amino acids

3 Protein folding is a spontaneous process that is driven by entropy. As a protein folds, nonpolar amino acids group together to avoid unfavorable interactions with polar solvent molecules.

A critical residue for the activation of Enzyme X is located in the amino acid sequence shown below (residues 141-147). AEKKSVG Enzyme X is activated by a kinase. Which of the following mutations would likely cause the largest decrease in Enzyme X activity? E142G K143R S14A V146I

3 Since Enzyme X is activated by a kinase, it must be phosphorylated. Serine has a side chain with a hydroxyl group and is the only amino acid listed that is typically phosphorylated. Mutating serine 145 to alanine would prevent phosphorylation, so it would cause the largest decrease in Enzyme X activity levels.

Which of the following characteristics regarding enzyme-substrate complexes can be explained by the induced fit, but not the lock-and-key, model? Reduction of the activation energy of the reaction Rigidity of the three-dimensional structure of the enzyme. Stabilization of the transition rate. Enzyme specificity.

3 The stabilization of the transition state is explained by the induced fit model, but not by the lock-and-key model. The induced fit theory posits that the active site of the enzyme is shaped by interactions between the active site itself and the substrate. The gradual molding of the active site to the substrate is what eventually stabilizes the transition state.

Protein X is a monomer that contains numerous antiparallel strands stabilized by hydrogen bonds that are enriched in lysine and aspartate. Based on this information, which of the following statements are likely true? Select all that apply. Protein X contains multiple polypeptide chains. Protein x is an integral membrane protein. Protein X contains at least one beta pleated sheet. Protein X contains at least one alpha helix.

3 We are told that protein X contains multiple antiparallel strands held together by hydrogen bonds. This is the definition of a beta pleated sheet.

Which of the following are the functional differences between DNA and RNA? The genome of viruses is exclusively composed of DNA. The inherent instability of RNA molecules when there's them unable to store genetic information. Certain RNA molecules possess the ability to catalyze biochemical reactions, while DNA molecules typically cannot

3 bc Ribozymes are RNA molecules capable of catalyzing biochemical reactions (such as RNA and DNA ligation and peptide bond formation). However, DNA molecules cannot catalyze biochemical reactions. not 1 bc Viruses can have either DNA or RNA genomes.

How does gene flow differ from genetic drift? Gene flow is a type of natural selection. Gene K Cruz three random chance alone. James Lue involves movement of alleles between populations by choice. Change the leads to fix station specific areas within a population of the time

3 genetic drift is random, Gene flow is migration

A novel hormone is found to require assistance from a transport protein to move throughout the circulatory system due to its poor solubility in aqueous solutions. Which other feature(s) can it be predicted to have? Select all that apply. Direction with transmembrane receptors. Molecular weight greater than 500 g per mole. Molecular weight less than 500 g per mole. Direction with nuclear receptors. Ability to freely diffuse through the plasma membrane. Inability to diffuse through the plasma membrane.

3,4,5 not 1 bc This is a feature of peptide hormones, and the question indicates that this novel hormone is a steroid hormone since it is nonpolar. not 2 bc This is a feature of peptide hormones, and the question indicates that this novel hormone is a steroid hormone. it is 3 bc The question stem states that this hormone is not soluble in aqueous solutions, meaning that it must be nonpolar. This means that it is a steroid hormone. They are also relatively small, with a common four-ring lipid structure derived from cholesterol. In contrast, peptide hormones are relatively large proteins. Therefore, we can also predict that the molecular weight of this hormone will be relatively small. it is 4 bc The question stem states that this hormone is not soluble in aqueous solutions, meaning that it must be nonpolar. This means that it is a steroid hormone. Steroid hormones freely diffuse through the plasma membrane and interact with nuclear receptors. it is 5 bc The question stem states that this hormone is not soluble in aqueous solutions, meaning that it must be nonpolar. This means that it is a steroid hormone. Steroid hormones freely diffuse through the plasma membrane and interact with nuclear receptors. not 6 bc This is a feature of peptide hormones, and the question indicates that this novel hormone is a steroid hormone.

The average molecular weight of an amino acid is 110 amu (or 110 Da), which we can estimate as roughly 100 amu for the purposes of initial estimations. A novel protein isolated from a bacterium is found to consist of 320 amino acids. Which of the following is the most reasonable estimate of its molecular weight? 3500 amu 6400 amu 35000 amu 64000 amu

35000 amu

Unlike speciation, adaptation: does not involve genetic mutations occurs in response to changing environmental conditions does not involve reproductive isolation is not influenced by selective pressures

3; Speciation occurs when two organisms undergo enough genetic change to become reproductively isolated. Adaptation is evolution on a smaller scale. It occurs when two populations of the same species adapt to slightly different environmental niches, but they are still capable of mating and reproducing offspring.

Inositol triphosphate (IP3) is a molecule released from the inner side of the cell membrane upon receptor binding at the cell surface. It initiates many signaling cascades within the cell. Disabling the IP3 pathway could be predicted to result in which of the following changes in a cell's responsiveness to hormonal signaling? Increase responsiveness to peptide hormones. Increased responsiveness the steroid hormones. Decreased responsiveness to peptide hormones. Decreased responsiveness to steroid

3rd. Peptide hormones bind with receptors on the external surface of the cell membrane because they cannot diffuse through the plasma membrane. Upon binding with membrane receptors, signaling in the cell is initiated via secondary messenger systems such as those modulated by IP3, as discussed in the question stem. Therefore, disabling the IP3 pathway would reduce the responsiveness of the cell to signals from peptide hormones. In contrast, steroid hormones freely diffuse through the cell membrane and interact with nuclear receptors inside the cell. These nuclear receptors regulate gene expression and are not involved with cytosolic second messenger systems like the IP3 pathway.

Suppose that the end product of a biochemical pathway allosterically inhibits an enzyme that functions earlier in the same pathway. The inhibitor regulates the enzyme through: Positive feedback which involves the formation of covalent bonds between the enzyme and inhibitor. Positive feedback which involves the formation of non-covalent bonds between the enzyme inhibitor. Negative feedback which involves the formation of covalent bonds between the enzyme inhibitor. Negative feedback which involves information of non-covalent bonds between the enzyme and inhibitor

4

The Strecker synthesis involves two stages, shown in picture Each stage has multiple steps in its reaction mechanism. Place steps I-IV that occur in stage 1 in their correct order. I. Nucleophilic attack by cyanide II. Loss of water III. Nucleophilic attack by ammonia IV. Protonation of the carbonyl

4 3 2 1 The first step in the Strecker synthesis is protonation of the carbonyl oxygen, followed by nucleophilic attack by NH3 on the carbonyl carbon. This produces a protonated amine, as shown below. Proton transfer occurs before loss of H2O. The final step that produces the ɑ-amino nitrile is nucleophilic attack by CN- at the electropositive carbon of the protonated imine.

If an M cyclin inhibitor was applied to epithelial cells in culture, then which of the following is most likely to occur? Cyclin dependent kinases levels would decline. Levels of other cyclones would likely increase to compensate. DNA replication might not occur. The mitotic spindle might not form.

4 Cyclins activate cyclin-dependent kinases, which phosphorylate protein targets that initiate a specific phase of the cell cycle. In the presence of an M cyclin inhibitor, the cultured cells would be unlikely to initiate or complete mitosis. Therefore, it is likely that the mitotic spindle would not form as prophase would not occur.

Which of the following enzymes is LEAST likely to be an oxidoreductase? Superoxide reductase. Xanthine dehydrogenase. NADH peroxidase. Carnitine decarboxylase

4 Decarboxylation is loss of a carboxylic acid group via bond cleavage; decarboxylases fall into the category of lyases, which catalyze non-hydrolytic cleavages.

Although inhibitors operate through different mechanisms, reversible inhibitors generally: Reduce enzyme activity by forming covalent bond to the enzyme. Reduce enzyme activity by interacting noncovalently with the enzyme. Block enzyme function by forming covalent bond to the enzyme. Block enzyme function by interacting noncovalently with the enzyme

4 Reversible inhibitors interact noncovalently with enzymes, which allows them to detach readily. Once bound, they tend to prevent the enzyme from functioning, such that only enzyme molecules not bound to an inhibitor molecule are able to catalyze the reaction.

Salt bridges are: Covalent bonds form between Polar amino acid side chains in influence tertiary but not quaternary structure Covalent bonds that form between polar amino acid side chains and influence both tertiary and quaternary structure. Ionic bonds that form between charged amino acid side chains and influence tertiary but not quaternary structure Ionic bonds that form between charged amino acid side chains of influence both tertiary and quaternary structure

4 Salt bridges are ionic bonds that form between a basic and an acidic amino acid, such as lysine and aspartate. These bonds are an important aspect of protein tertiary structure and quaternary structure, since they influence protein folding and subunit assembly.

Tertiary structure is driven by all of the following interactions EXCEPT: The formation of salt bridges between charged residues. The tendency of nonpolar amino acids to group together. Hydrogen bonding between polar side chains. The reduction of cysteine residues to form disulfide bonds.

4 This statement is nearly correct, but cysteine residues are oxidized, not reduced, during disulfide bond formation.

The allele W, for white wool, is dominant over the allele w, for black wool. If 16% of a sheep population is black, and the population is unaffected by evolutionary forces, what percentage of the population is heterozygous for wool color? 36% 40% 48% 60%

48% Use the HW equations to solve. The HW equations are p+q=1 and p2+2pq+q2=1: 1. The homozygous recessive genotype frequency is provided q2 = 0.16. 2. Take the square root of .16 to find q. The black allele frequency (q) is 0.4. 3. Since the frequencies of the recessive and dominant allele must add to 1, p = 0.6. This is the frequency of the white allele. 4. According to the Hardy-Weinberg equation, 2pq is equal to the frequency of the heterozygous genotype. Plugging in the values for p and q, we get 2pq = (2)(0.4)(0.6) = 0.48. In other words, 48% of the sheep population is heterozygous for wool color.

Should these cell types is least likely to express the enzyme telomerase? HeLa cells which are derived from cervical cancer cells. Hematopoietic stem cells. Embryonic stem cells. Adult B lymphocytes.

4th bc Adult somatic cells, such as B lymphocytes, have little telomerase activity as they do not need to divide frequently. not the 2nd bc These cells must divide often. Thus, telomerase is a necessary enzyme to express to preserve their telomere lengths.

At which of the following pH levels would a lysosome's enzymes function best? If Acidic pH < 7 1 5 7 9

5 Lysosomes are spherical organelles that contain enzymes that best function under slightly acidic conditions (pH 4.5-5.0) and can break down most biomolecules. Lysosomes act as the cell's waste disposal system by digesting unwanted materials.

Glucose 6-phosphate dehydrogenase catalyzes a reaction involving glucose 6-phosphate. What is the most likely product formed in this reaction? 6 phosphogluconolactone glucose glucose 1 phosphate fructose 6 phosphate

6 phosphogluconolactone Even if the pentose phosphate pathway is unfamiliar, focusing on the type of enzyme in conjunction with process of elimination can help you arrive at the correct answer. Phosphogluconolactone contains word stems that can be used as clues, such as 'phospho' and 'gluco'. The lactone ending suggests a C=O bond resulting from oxidation of an O-H, i.e. a redox process catalyzed by the oxidoreductase enzyme glucose 6-phosphate dehydrogenase.

Suppose that a population of deer is in Hardy-Weinberg equilibrium and that all deer within this population have either straight or curved horns, and curved horns are dominant to straight horns. The frequency of the allele for curved horns is 0.7. What percentage of the deer have straight horns? 9% 30% 42% 49%

9% Use the HW equations to solve (p+q=1 p2+2pq+q2=1) 1. Find the frequency of the straight horns allele (q) within the population. From the question stem, we know that p = 0.7. Plug this into the equation p + q = 1 to obtain 0.3 for q. 2.From the Hardy-Weinberg equation, we know that q2 is the percentage of deer that are homozygous recessive, so we can simply square 0.3 to get the correct answer: 0.09 or 9%.

Which of the following amino acids would likely compose an internal alpha helical domain of a receptor embedded within the cell membrane? Select all that apply. ALA HIS PRO ASP

ALA First, recall that alpha helices are stabilized by hydrogen bonding between backbone atoms. Therefore, all amino acids are good candidates unless they disrupt the hydrogen bonding pattern or have R group properties that make them unsuitable for the environment in which the helix will be located within the cell. Remember that alpha-helix amino acids have their R-groups pointing outwards, towards the surroundings of the helix. Because we are talking about a receptor which will be embedded into the membrane, we are looking for nonpolar amino acids. Alanine is a perfect fit.

What happens to osmotic pressure when the temperature is decreased to one-third the original value and the concentration of solutes increases fourfold? pi = IMRT The osmotic pressure decreases by half. The osmotic pressure increases 0.75 fold. The osmotic pressure increases 5.2 fold. the osmotic pressure increases 1.3 fold

According to the osmotic pressure formula, π = iMRT, the osmotic pressure (π) is directly proportional to temperature (T) and solute concentration (M). Increasing the solute concentration by a factor of 4 and decreasing the temperature by one-third would leave us with a net increase in osmotic pressure of approximately 1.3 fold.

Aminonitrile and NH4Cl. Strecker or Gabriel? Malonic ester and hydrazine. Strecker or Gabriel?

Aminonitrile and NH4Cl = strecker malonic esther and hydrazine = gabriel

Which of the following terms must refer to a negatively-charged compound? Select all that apply. Glutamic Acid Aspartic Acid Aspartate Glutamate

Aspartate and Glutamate

Which of the following is NOT a similarity between nuclei and mitochondria? Double membrane Presence of DNA Membrane-embedded proteins Use of binary fission

Binary fission While the nucleus divides during mitosis, only mitochondria replicate independently of the cell cycle (via binary fission).

Which of the following would be significantly increased by mutations affecting microtubule function? Select all that apply. Birth defects Mucus build up in throat Male sterility DNA replication errors

Birth defects Mucus build up in throat Male sterility Mutations affecting microtubules would cause birth defects by impacting the ability for chromosomes to be "pulled apart" during anaphase of meiosis. Mutations affecting microtubules would cause mucus buildup in the throat by inhibiting throat epithelial cells' ciliary action, which normally clears debris in the throat. Mutations affecting microtubules could cause male sterility in at least two ways: 1) chromosomal nondisjunction might affect cellular functionality, and 2) flagellum dysfunction would inhibit sperm motility.

A biochemist is evaluating an unknown inhibitor and determines that it does not bind to its target enzyme in the absence of substrate. Based on this information, which of the following mechanisms of inhibition are NOT possible? Select all that apply. Competitive inhibition. Noncompetitive inhibition. Uncompetitive inhibition. Mixed inhibition.

Competitive inhibition & Noncompetitive inhibition. Competitive inhibitors bind to the free enzyme at the active site. Since the unknown inhibitor does not bind the free enzyme, it cannot be a competitive inhibitor. Noncompetitive inhibitors bind to enzymes at an allosteric site, regardless of whether the substrate is already bound. If the unknown inhibitor was noncompetitive, it should be able to bind the enzyme in the absence of substrate.

Which of the following would NOT be considered an energy source for primary active transport? Light. Concentration gradient. ATP. Redox reactions

Concentration gradient. bc it can be used to power secondary active transport and is the driving force behind forms of passive transport. Primary active transport is not powered by a concentration gradient. Rather, primary active transport can be used to set up a concentration gradient that can be used to power secondary active transport.

In physics, there are four fundamental forces that explain all interactions in the universe: gravitation, electromagnetism, and the strong and weak nuclear forces. Which of these forces primarily drives metabolic processes?

Electromagnetism. All charge and polarity-based interactions are driven by the electromagnetic force. This answer is further supported by the importance of oxidation/reduction reactions in metabolism, which involve electron transfer, as well as the fact that organic chemistry mechanisms involve moving electrons around.

Which of the following types of cells are most likely to contain large amounts of smooth ER? Neurons RBC Epithelial liver Cells Cardiac Muscle Cells

Epithelial liver Cells The smooth endoplasmic reticulum (ER) is a membrane-bound organelle that participates in lipid synthesis, calcium ion storage, and detoxification. The liver is a site of extensive detoxification and lipid metabolism. Therefore, liver cells have abundant smooth ER.

Which of the following amino acids are aromatic? Select all that apply. F L M V W Y

F W Y

True or false: Single nucleotide polymorphisms necessarily result in differences in the amino acid sequence of a protein. True or false: Centromeres contain highly conserved gene sequences. (A highly conserved sequence is one that has remained relatively unchanged far back up the phylogenetic tree, and hence far back in geological time.)

F. Single nucleotide polymorphisms (SNPs) are single-nucelotide substitutions at a specific genetic locus. They may result in different amino acid substitution at the SNP's position, or the SNP may still encode the same amino acid as the original sequence. Furthermore, many SNPs fall in non-coding regions of the genome and consequently do not affect protein sequences. F.Centromeres are the sites of attachment for sister chromatids and contain repetitive DNA highly condensed as heterochromatin. Although centromere structure is integral to cell function, the centromeric DNA sequence itself is not highly conserved.

True or false: Dyneins are the accessory proteins that carry neurotransmitter-containing vesicles to a neural synapse.

False Kinesins, not dyneins, move from the center of the cell towards the cell's edge. Kinesins move towards the plasma membrane and the synapse. On the contrary, dyneins travel from the cell's edge (or synapse) towards the cell center.

Which of the following is a function of the rough endoplasmic reticulum? Folding and modifying newly synthesized proteins digesting toxic materials in the cytoplasm Packaging proteins for leaving the cell Transporting proteins to the Golgi apparatus

Folding and modifying newly synthesized proteins Ribosomes bound to the rough ER synthesize proteins. Within the ER, newly-synthesized proteins may be modified or folded with the help of chaperone proteins.

Of the options below, which of the following is a single actin monomer? F-actin G-actin H-actin Keratin

G-actin G-actin, or globular actin, is a single actin monomer. Recall that G-actin is the monomeric form of actin that polymerizes to form F-actin. Can't be F-actin bc F-actin is the polymeric and multimeric form of actin (multiple actins polymerized together). A multimeric protein describes a protein that contains two or more subunits. H-actin doesn't exist Keratin is an intermediate filament. It is not composed of actin.

Which of the following amino acids, as indicated by their three-letter abbreviations, contains a functional group that most typically functions as a proton acceptor? Select all that apply. His Lys Asp Arg Glu Asn

His, Lys, Arg According to the Brønsted-Lowry definition, bases are proton acceptors. Histidine (His), lysine (Lys), and arginine (Arg) are the three basic amino acids.

What characteristics could prevent a molecule from diffusing across the plasma membrane? Select all that apply Hydrophobicity. Hydrophilicity. Small size. Non-polar. Large diameter. Polar. High surface area to volume ratio. Amino acid-based

Hydrophilicity, large diameter ,polar

Which of the following modifications to an enzyme-catalyzed reaction would affect its maximum velocity? Select all that apply. Increasing the enzyme concentration. Decreasing the substrate concentration. Adding a competitive inhibitor. Add an uncompetitive inhibitor. Adding a noncompetitive inhibitor.

Increasing the enzyme concentration, Add an uncompetitive inhibitor, Adding a noncompetitive inhibitor The concentration of enzyme determines the maximum reaction rate. When we add more enzyme, more substrate will be converted into product over time. Uncompetitive inhibitors bind to enzyme substrate complexes, which prevents affected enzymes from converting substrate to product molecules, thereby reducing the maximum reaction speed. Noncompetitive inhibitors bind to allosteric sites on an enzyme, blocking enzymatic activity regardless of whether the substrate is bound to the enzyme. Since this reduces the number of functional enzymes, the maximum reaction rate declines.

Which of these events is most directly responsible for the release of neurotransmitter molecules from synaptic vesicles at the axon terminal? Influx of extracellular Na Efflux of intracellular K Influx of extracellular Ca Influx of extracellular Neurotransmitter

Influx of extracellular Ca Membrane depolarization at the axon terminal causes voltage-gated calcium channels to open, resulting in calcium influx. This increase in intracellular calcium causes conformational changes in calcium-sensitive vesicle docking proteins, ultimately leading to release of neurotransmitter molecules.

All naturally synthesized amino acids in humans are in the __ configuration. S R L D What is the IUPAC name for alanine?

L 2-Aminopropanoic acid

Which of the following would you expect to be ingested via receptor - mediated endocytosis? Select all that apply. Dissolved electrolytes. Food particles. Solvents. Bacteria. Low density lipoproteins

Low density lipoproteins

Which two amino acids contain sulfur? A L M C P True or false: Gln has a longer side chain than Asn.

M is the 1-letter abbreviation for methionine; C for cysteine, and both contain sulfur. True

Place the following fibers in order of decreasing diameter: microtubules, actin microfilaments, and intermediate filaments.

Micro, Inter, Actin Microtubules have a larger diameter (25 nm) than do intermediate filaments (10 nm), which have a larger diameter than do actin microfilaments (6 nm).

Neurotransmitters are delivered by kinesins, taken from the cell body of a neuron to the axon terminal. Neurons must have extensive: Keratin Microfilaments Microtubules Intermediate filaments

Microtubules are tracks made of tubulin which extend out from the microtubule organizing center of a cell. They are heavily implicated in transporting cargo around a cell - for example, vesicles containing neurotransmitters. Kinesins and dyneins are motor proteins which "walk" along microtubules like a road.

Which of the following organelles is capable of replicating itself? Mitochondrion Ribosome Golgi Apparatus Endoplasmic Reticulum

Mitochondria they have their own DNA genome, separate from the cell's nuclear genome. This allows mitochondria to replicate independently of the cell cycle.

Pick which one is the reduced form NAD+ or NADH FAD or FADH

NADH and FADH

Threonine deaminase catalyzes the conversion of L-threonine to alpha-ketobutyrate and ammonia. Kinetics experiments have shown that this enzyme is subject to complex allosteric control. It is inhibited by isoleucine, which is the end product of the pathway in which it functions, and it is activated by valine, which is generated in a separate pathway. Based on this information, threonine deaminase is regulated through which of the following mechanisms? + feedback - feedback feed forawrd both +/- feedback

Neg Negative feedback regulation occurs when a downstream product of a pathway inhibits an enzyme that functions earlier in the pathway. The net result is that the pathway gets shut off when there is plenty of product. Since isoleucine is the end product of the threonine deaminase pathway, isoleucine regulates threonine deaminase through negative feedback.

mixed inhibition Competitive inhibition uncompetitive inhibition noncompetitive inhibition

Noncompetitive inhibition The Michaelis-Menten curve shows a decrease in Vmax when the inhibitor is added, which is consistent with noncompetitive inhibition. Remember that Vmax is the reaction rate at which the curve plateaus horizontally. Next, let's check Km. If we divide each Vmax in half, draw a line out horizontally to each curve, and then drop it down to the x-axis, we end up at approximately the same substrate concentration. Since Km remains the same, the unknown inhibitor is most likely a noncompetitive inhibitor.

Which of the following is NOT a tenet of cell theory? All cells are capable of reproducing The cell is the basic unit of life All cells arise from pre existing cells All organisms are composed of one or more cells

Not all cells are capable of producing some cells (such as mature erythrocytes that do not possess nuclei) do not reproduce

In which of the following structures are ribosomes assembled? Nucleolus Cytoplasm Cell membrane Mitochondrial membrane

Nucleolus The nucleolus is a structure within a eukaryotic nucleus that is primarily responsible for ribosome synthesis and assembly. Ribosomes are RNA-protein complexes that translate mRNA into protein.

The administration of a specific antimitotic drug to E. coli would almost certainly result in cell death. This is false. Why? Hint: it has something to do with being a prokaryote

Prokaryotes do not undergo mitosis. Consequently, drugs that specifically target the mitotic process should have minimal effects on bacteria.

Which of the following are most likely NOT potential functions of cytoskeletal capping proteins? Select all that apply. Cell movement Promoting cytoskeletal polymer degradation Muscle contraction Promoting the Krebs cycle

Promoting cytoskeletal polymer degradation: Capping proteins inhibit cytoskeletal protein degradation by preventing actin polymer breakdown. Promoting the Krebs cycle: Aerobic respiration (including the Krebs cycle) occurs in mitochondria to provide cellular energy as ATP. As the Krebs cycle occurs in the mitochondria, it is likely unrelated to cytoplasmic cytoskeletal proteins, such as actin and microtubules.

In the stomach, proteins are broken down primarily by: Acidic conditions. Proteases.

Proteases (shocker!) bc The protease pepsin is the main driver of peptide bond breakdown in the stomach. Although it is true that the stomach is a highly acidic environment, and peptide bonds can be broken down by acidic conditions. However, the acidic environment of the stomach primarily serves to activate the molecule pepsin from the inactive pepsinogen, which in turn is responsible for peptide bond breakdown.

A cell is isolated that contains no organelles. Which of the following cell types is this cell most likely to be? Platelet Red blood cell Leukocyte Neuron

RBC Red blood cells expel their nuclei, genetic material, and organelles during their maturation process. MCAT® questions often test this understanding. For example, "mature red blood cells" would likely answer a question that asks which cell type is least helpful for studying genetic mutations. Can't be platelets bc Platelets are cell fragments, not cells. Therefore, they do not contain organelles.

Suppose we encounter life on another planet. Which of the following discoveries would indicate that their metabolic pathways function extremely differently to humans? Do use of seven carbon carbohydrates rather than six carbon carbohydrates for metabolic purposes The presence of an additional carbon in all amino acids. Metabolic pathways that bypass redox reactions. The use of cytosine triphosphate instead of ATP for intracellular energy

Redox

Which of the following statements are true regarding protein secondary structure? Select all that apply. It is the second layer of protein folding. It refers to local regions of protein folding. It is limited to alpha helices and beta pleated sheets. It involves interactions between amino acid side chains. Is stabilized by hydrogen bonding.

Refers to local regions of protein folding and is stabilized by hydrogen bonding

What is the earliest stage of the cell cycle in which a cell has sufficient genomic material to undergo mitosis? G1 G2 S M

S phase is cell cycle stage that the cell replicates its DNA. Consequently, the cell has sufficient genomic material to undergo mitosis by S phase's completion.

During which phase of the cell cycle does DNA replicate? G1 G2 S M

S phase of the cell cycle. The cell cycle includes a growth phase (G1), an S phase (DNA replication), a second growth phase (G2), and mitosis (cell division).

SEVEN UP acronym for the path taken by spermatozoa

Seminiferous tubules Epididymis Vas deferens Ejaculatory ducts Nothing (placeholder) Urethra Penis

Osmotic pressure depends on all of the following EXCEPT: Solvent concentration. Number of dissolved particles in a certain volume of solution. Temperature. Ideal gas constant

Solvents concentration bc they do not have concentrations. Concentration describes the quanity of dissolved solutes per unit of solvent. While osmosis describes solvent movement across a membrane driven by a solute concentration differential across a membrane, solvent concentration is not a factor of osmotic pressure.

Where do lysosomal enzymes originate? Packaged at Golgi Apparatus Synthesized at ER Pinched off from cell membrane Imported from outside the cell

Synthesized at ER Lysosomal enzymes are proteins that are synthesized in the rough endoplasmic reticulum. After synthesis, they are packaged within the Golgi apparatus into lysosomes, where they break down waste.

Telomerase replicates the ends of chromosomes using a(n) ______ template. DNA RNA protein lipid

Telomerase uses an RNA template complementary to the 5'-TTAGGG-3' (the telomere repeat) to replicate chromosome ends.

The smooth ER participates in several metabolic processes, including ___ synthesis, ___ metabolism, and ___. They have 3 functions:

The smooth ER participates in several metabolic processes, including lipid synthesis, carbohydrate metabolism, and detoxification. lipid synthesis, detox, steroid hormone synthesis

True or false: Secretory proteins are transported from the endoplasmic reticulum to the trans-face of the Golgi apparatus.

This statement is false. Secretory proteins are transported from the endoplasmic reticulum to the cis-face of the Golgi appartus. There, they will undergo packaging as they are transported first to the medial- then trans-face of the Golgi apparatus, before release in the form of vesicles that can subsequently fuse with the plasma membrane to exocytose their contents.

True or false: According to the Michaelis-Menten equation, reaction rate = (½ Vmax [S]) / (Km + [S]).

This statement is false. This equation would yield a reaction rate that is half the size that it should be. The Michaelis-Menten equation states that reaction rate is equal to (Vmax [S]) / (Km + [S]).

Which of the following are NOT part of a replicated chromosome? Select all that apply. Tubulin. Centromere. Sister chromatids. Histones.

Tubulin. Polymerized tubulin is a fibrous protein that enables cells to undergo mitosis. It is found in spindle fibers, but is not part of the replicated chromosome.

Several molecules that assist catalysis are listed below. Which of these molecules are coenzymes? Select all that apply. Ca2+ Vitamin B12 Magnesium FAD

Vitamin B12, FAD

Brønsted-Lowry acids proton ___; bases are proton ___

acids are proton donors and bases are proton acceptors

Tertiary structure includes which of the following interactions between amino acids? Select all that apply. Hydrogen bonding ionic bonding covalent morning hydrophobic interactions

all

Which of the following forms of transport are considered passive? Select all that apply. Osmosis oxygen diffusion aquaporin - mediated transport ion channel mediated transport

all

Which of the following forms of transport are considered passive? Select all that apply. Osmosis. Oxygen diffusion. Aquaporin mediate transport. ion channel mediated transport

all

Select all that apply that complete the following statement. In the human cell, nucleic acids can be found in: the nucleus mitochondria cytoplasm smooth ER

all 3 except smooth er

Which of the following can be features of active transport? Select all that apply. Requires energy. Establishes a concentration gradient. No direct consumption of ATP. A sodium potassium pump

all even C because Active transport requires the consumption of energy, usually through ATP hydrolysis, either directly (primary) or indirectly (secondary). In secondary active transport, active transport generates a concentration gradient that powers the passive transport of something else. More specifically, the spontaneous transport of one substance down its electrochemical or concentration gradient is coupled to the non-spontaneous transport of another substance against its gradient. Secondary active transport is not directly powered by ATP.

Which of the following are components of nucleosomes? Select all that apply. Amino acids. Deoxyribonucleotides. Ribonucleotides. Phosphate groups

all except Ribonucleotides.

Which of the following are examples of diffusion? Select all that apply. Dissolved glucose molecules move randomly in solution until the concentration of glucose throughout the solution is equal. Enter glucose moves down its concentration gradient into the cell through symporter protein channel. Large amounts of water enter and exit the cell through Aquaporins. A lipid soluble hormones enters a sound travels to the nucleus to regulate transcription

all except the 2nd one bc it uses a symporter, which is active transport. the last one is correct too bc A lipid-soluble molecule is hydrophobic and can therefore diffuse down its concentration gradient across the hydrophobic plasma membrane core. As this molecule is a hormone, it travelled through the circulatory system to reach this cell. Therefore, assume there is a higher hormone concentration extracellularly than intracellularly. Thus, when the hormone crosses the plasma membrane. it is passively diffusing down its concentration gradient.

Which of the following are the most likely regulators of an energy-producing pathway? Select all that apply. Energy levels within the cell. Byproducts of the pathway. Hormonal signaling. Body temperature

all of them apply

Suppose that a researcher has designed a reversible inhibitor of a kinase that is overexpressed in certain cancer cell lines. In the presence of the inhibitor, the kinase's affinity for its substrate declines and phosphorylation rate is reduced even at extremely high substrate concentrations. The inhibitor most likely binds to: The enzyme substrate complex. The empty active site of the enzyme. The allosteric site of an enzyme. Neither the active site of the enzyme or an allosteric site

allosteric site on enzyme Several types of reversible inhibitors bind allosteric sites. Noncompetitive inhibitors do not affect substrate binding affinity; the researcher's new inhibitor cannot be noncompetitive. However, certain mixed inhibitors which prefer to bind the free enzyme rather than ES, reduceVmax and may also reduce the substrate's affinity for the enzyme, causing an increase in Km.

Identify the term that is correctly defined. A peptide is any structure containing and my bonds. an oligopeptide is a composed of 2 to 20 amino acid residues. A protein is a long unbranched chain of amino acids. A polypeptide contains one or more peptide chains

an oligopeptide is a composed of 2 to 20 amino acid residues. "Oligo-" means "few," so an oligopeptide is a peptide composed of a few (2-20) amino acid residues."Peptide" is a general term that refers to a short amino acid chain with up to 50 amino acid residues that are connected to each other by amide bonds.

Which of the following transport channels use secondary active transport? Select all that apply. Anti-porters. ATP synthase. Electron transport chain complex. Ligand gated calcium channels

antiporters Secondary active transport is a combination of active and passive transport. The active transport generates a concentration gradient that powers the passive transport of something else. Antiporters move two solute types in opposite directions. One solute moves with its concentration gradient and the other moves against its own concentration gradient.

Which of the following amino acids, as indicated by their three-letter abbreviations, contain a functional group that primarily functions as a proton donor at physiologiccal pH? Select all that apply. asn lys asp arg glu gly

asp glu According to the Brønsted-Lowry definition, acids are proton donors. Aspartic acid (Asp) and glutamic acid (Glu) are the two acidic amino acids, making them the correct answers to this question.

Which of the following statements about primary active transport is/are FALSE? Select all that apply. Proton pumps of the electron transport chain are involved in the direct hydrolysis of ATP. Proton pumps of the electron transport chain transport protons down there concentration gradient to drive the synthesis of ATP

both

Sulfanilamide is a common antibiotic that functions as a substrate analog for dihydropteroate synthase (DHPS), a bacterial enzyme that catalyzes an intermediate step in folate synthesis. Sulfanilamide is most likely a(n): mixed inhibition Competitive inhibition uncompetitive inhibition noncompetitive inhibition

competitive inhibitor Substrate analogs share structural features with the enzyme's endogenous substrate, which allows them to bind to the active site.

Which of the following statements are true of all enzymes that exhibit cooperativity? Select all that apply They contain multiple active sites. They are allosterically regulated. Substrate binding changes binding affinity for the substrate. Substrate binding at one side promotes substrate binding at another site

everything but 4 bc This statement describes positive cooperativity, which is not the only type of cooperative binding that exists. Some enzymes display negative cooperativity, which occurs when substrate binding at one site reduces the affinity of other active sites for the substrate.

True or false: Coenzymes are defined as cofactors that are covalently linked to the enzymes they assist.

false. Although coenzymes can be covalently bound to enzymes, this is not true of all coenzymes. Coenzymes are simply cofactors with an organic structure.

True or false: Protonating aniline (C6H5NH2) to form C6H5NH3+ would improve its solubility in hexane, a nonpolar solvent.

false. As the question indicates, protonating aniline would make it positively charged. Charged substances are poor solutes in nonpolar solvents such as hexane.

True or false: Based solely on the observation that in the presence of 2,3-bisphosphoglyceric acid (2,3-BPG), the metalloprotein hemoglobin exhibits a diminished ability to bind oxygen, we can conclude that 2,3-BPG is an allosteric regulator of hemoglobin.

false. In fact, 2,3-BPG is indeed an allosteric regulator of hemoglobin, but the information given in the question stem is not sufficient to reach this conclusion. In order to conclude that 2,3-BPG is an allosteric, not an orthosteric, regulator, we must have some information indicating that it does not bind at the active site of hemoglobin.

True or false: Michaelis-Menten plots show how changes in enzyme concentration affect the rate of an enzyme-catalyzed reaction.

false. Michaelis-Menten plots show how changes in SUBSTRATE concentration affect the speed of the reaction. Enzyme concentration is held constant in Michaelis-Menten kinetics experiments.

True or false: Primary structure refers to the noncovalent interactions between amino acids within a peptide or protein

false. Primary structure refers to the linear chain of amino acids that forms the backbone of a protein or peptide. These amino acids are covalently linked. Noncovalent interactions are a feature of secondary and tertiary structure.

True or false: Proline can break up secondary structure motifs because of its unusually strong hydrogen bonding.

false. Proline does have the ability to break up secondary structure motifs, but it can do so because its side chain has the unique property of connecting back to the amino acid backbone, not because it engages in unusually strong hydrogen bonding.

True or False: Prosthetic groups typically assist enzymes by transporting functional groups from one cellular location to another.

false. Prosthetic groups are permanently bound to the enzymes they assist, so they cannot travel from place to place. They tend to play a specific role in the catalytic mechanism that occurs in the active site.

True or false: both kinases and phosphatases catalyze their respective reactions through an addition of water.

false. While a phosphatase does catalyze the removal of a phosphate through a hydrolysis reaction, a kinase does not catalyze the transfer of a phosphate through a hydrolysis reaction.

True or false: Two organisms must not be able to produce viable offspring in order to be considered members of two different species.

false; mules Although most species are reproductively isolated, there are some separate species that can reproduce and generate viable offspring. For example, a horse and a donkey can reproduce. Their offspring is a hybrid mule. In these cases, the offspring, such as the mule, are often infertile.Note that the MCAT® is unlikely to test the various definitions of the species concept, but that the biological species concept (used above) is the one you will most likely encounter unless specified otherwise.

The formation of a peptide bond can be classified as what type of reaction? Select all that apply. Dehydration. Nucleophilic substitution. Condensation. Hydrolysis

first 3

Trypsin, an enzyme found in the duodenum of the small intestine, plays an important role in breaking down proteins in ingested food. This enzyme most likely belongs to which classification(s) of enzymes? Select all that apply. ligase oxidoreductase hydrolase isomerase protease

hydro and protease The question stem indicates that trypsin is a protease, or an enzyme that breaks down proteins. Most proteases are hydrolase enzymes, meaning that they break bonds via the addition of water. Note that enzymes can belong to multiple categories: hydrolase is the more general category, and protease is a specific category of hydrolases.

Which type of bond is primarily responsible for maintaining the secondary structure of a protein? Covalent bond. Hydrogen bond. Ionic bond. Disulfide bond.

hydrogen bond. The secondary structure of a protein is formed through hydrogen bonding interactions between backbone atoms of the constituent amino acids.

If there is a lower relative extracellular concentration of solutes, the solution is: hypertonic hypotonic isotonic

hypo. "Hypotonic", "hypertonic", and "isotonic" describe a cell's solute concentration relative to the solute concentration of the surrounding solution. A hypotonic solution has a lower extracellular solute concentration. If a cell is placed in a hypotonic solution, there will be a net flow of water into the cell.

If there is a lower relative extracellular concentration of solutes, the solution is hypotonic hypertonic isotonic

hypotonic because "Hypotonic", "hypertonic", and "isotonic" describe a cell's solute concentration relative to the solute concentration of the surrounding solution. A hypotonic solution has a lower extracellular solute concentration. If a cell is placed in a hypotonic solution, there will be a net flow of water into the cell.

Which of the following statements comparing symporters and antiporters in the plasma membrane is FALSE? Select all that apply. Both symporter is an anti-porters are examples of primary active transport but only symporters move molecules down there concentration gradient. Both supporters and anti-Porter is used osmotic pressure to drive transport but symporter's transport molecules in the same direction while anti-porters transport molecules in opposite directions. Both symporters and anti-porters are examples of secondary active transport but only anti-porters will always promote the movement of molecules into the cell. Both importers and anti-porters help molecules diffuse down there concentration gradient but when does so using facilitated diffusion while the other does Sophia osmosis

it's all three except for the third one. not the third one bc: Symporters and antiporters use secondary active transport, as they do not directly consume energy. Both allow molecules to move down their concentration gradients to harness their energy to power an unfavorable transport task. More specifically, the spontaneous transport of one substance (usually an ion) down its electrochemical or concentration gradient is coupled to the non-spontaneous transport of another substance against its gradient. Both symporters and antiporters can move molecules into the cell.

kinases phosphatases oxidoreductases none of the above

kinases It is clear in step A that a phosphate is being added to glucose to form glucose 6-phosphate. Thus, a kinase is very likely involved. In most cells, the kinase that mediates this step is hexokinase. In special cells, including those of the liver, the kinase responsible is a specific hexokinase isoform called glucokinase.

Which of the following features are common to all proteins that exhibit positive cooperativity? Select all that apply. Hill coefficient less than 1 catalytic activity sigmoidal substrate binding curve multiple substrate binding sites

last 2

Initital enzyme-substrate binding involves which of the following interactions? Select all that apply. polar covalent bonds nonpolar covalent bonds steric effects hydrophobic interactions hydrophilic interactions

last 3

Research has found that certain amino acid residues in histones can be phosphorylated through the enzyme-catalyzed addition of a PO32− group. If DNA is negatively-charged, which of the following is the most likely effect of histone phosphorylation? Lower levels of transcriptional activity. Increase levels of oxidative stress experience by DNA. Decreased levels of oxidative stress experience by DNA. Loosening of the DNA coiled around histones

last. The question stem indicates that phosphorylation adds a strongly negatively charged group to histones. These groups will experience electrostatic repulsion from the negatively charged phosphate groups on the DNA backbone, because like charges repel. This means that the histones will associate more loosely with the DNA, providing more room for transcription factors.

Which of the following statements are true of positive feedback regulation in biological systems? Select all that apply. helps maintain homeostasis leads to activation of enzymes amplify physiological processes generally paired with negative feedback mechanisms

leads to activation of enzymes, amplify physiological processes, generally paired with negative feedback mechanisms

DNA repair requires several specialized enzymes, which must be able to access the damaged region of DNA in order to function properly. If DNA is negatively-charged, which histone modification would NOT create space for these enzymes to work? Serine phosphorylation (change OH- to OPO3(2-) ) Lysine methylation (NH3+ to NH2+CH3)

lysine methylation As described in the answer choice, methylating lysine does not change its charge, and therefore does not create space by weakening the attraction between positively-charged lysine residues and the negatively-charged phosphate backbone of DNA.

If a cell has 42 chromosomes to begin with, how many does it have after meiosis II? 21 42 63 84

meiosis produces haploids from diploids remember Meiosis is associated with sexual reproduction, where an organism produces haploid gamete cells from a diploid parental cell. At the end of meiosis II, the daughter cells will have half the chromosome number as the parental cell.

If a person had a genetic mutation that impaired the microtubules from forming efficiently, which of the following would NOT occur? Cells would have difficulty completing mitosis Neurons would have difficulty secreting neurotransmitters All motile cells would have difficulty moving Vesicular transport would be disrupted

motile cells can't move While flagellated and ciliated cells would have trouble moving, many cells (like the immune system cells) rely on actin reorganization for motility, and would thus be unaffected.

In which stage, if any, does a cell become committed to the cell cycle? G1 G2 S

n G1, the most crucial growth phase, the cell makes organelles and proteins to support two progeny cells. If a cell is able to invest enough resources into doubling the necessary structures and machinery, the cell "commits" to the cell cycle. The cell cycle may be interrupted after this checkpoint, but such circumstances are uncommon.

What will be the net direction of water movement when there is 1M NaCl on the right side of a membrane and 2M glucose on the left side of the membrane? net movement to the left side net movement to the right side no net movement net movement of glucose to right, net movement to NaCl towards left

no net movement of water. For osmosis, it is the total solute molecule concentration that matters, even if they're chemically different. A 1M solution of NaCl will create 2M total ions: 1M of Na+ and 1M of Cl-. 2M of ions on one membrane side and 2M of glucose on the other membrane side results in no net movement of water across the membrane.

What will be the net direction of water movement when there is 1M NaCl on the right side of a membrane and 2M glucose on the left side of the membrane?

no net mvmt. For osmosis, it is the total solute molecule concentration that matters, even if they're chemically different. A 1M solution of NaCl will create 2M total ions: 1M of Na+ and 1M of Cl-. 2M of ions on one membrane side and 2M of glucose on the other membrane side results in no net movement of water across the membrane. D

A researcher discovers that a particular inhibitor does not affect Km, but reduces Vmax. This inhibitor is most likely: mixed inhibition Competitive inhibition uncompetitive inhibition noncompetitive inhibition

noncompetitive inhibitionis correct. Noncompetitive inhibitors bind to enzymes allosterically regardless of whether substrate is bound at the active site. They do not affect Km. The enzymes that are not bound by the inhibitor are free to catalyze the reaction normally, but Vmax is reduced as fewer active enzymes are available to catalyze the reaction.

Of the following stages of mitosis, which is the earliest that genomic material is haploid? propahse metaphase anaphase none of the above

none. In mitosis, a diploid parental cell generates two diploid daughter cells. There is no mitosis stage in which a cell has a haploid genotype.

In the electron transport chain, electrons are transferred from electron carriers to protein complexes, which generate an electrochemical gradient used to make ATP. Which class of enzymes is most likely responsible for this transfer of electrons? hydrolases oxidoreductases ligases transferases

oxidoreductases The electron carriers involved in this process are NADH and FADH2. The transfer of electrons from these carriers to protein complexes is facilitated by oxidoreductases, which are responsible for catalyzing redox reactions. When a process involves the transfer of electrons, it is likely that this class of enzymes is involved.

A loss-of-function mutation in a gene that codes for tubulin would most directly inhibit which of the following processes in meiosis? Chromie duplication Chromie separation Genetic recombination Chromie condensation

separation Chromosome separation occurs during anaphase. The cell spindle coordinates chromosome separation and is made of microtubules. Microtubules are tubulin polymers.

A microfilament capped at the plus (+) end would tend to: grow stay the same length shrink idk u can't predict

shrink Capping prevents the addition or removal of monomers to the capped end of the filament. Actin filaments capped at the plus (+) end would likely shrink, as actin monomers readily fall off the minus (-) end, shrinking the filament size. can't stay the same length bc that only occurs when a microfilament is capped at both ends can't grow bc that only occurs when a microfilament is capped at the minus end

Which of the following statements are true of peptide bonds? Select all that apply. they are amide bonds covalent bonds highly flexible stabilized through resonance vulnerable to changes in temp and pH

they are amide bonds covalent bonds stabilized through resonance

truncated proteins are created when there is a premature stop codon. T/F? Bonus: what are the three stop codons (Think of the start codon)

true In humans, the three stop codons are UAA, UAG, and UGA. Since the mRNA transcript consists of four codons, divide the sequence into three-nucleotide segments.

True or False: The primary difference between facilitated diffusion and passive diffusion is the presence of a protein channel with facilitated diffusion.

true. Facilitated diffusion does not require any energy (either directly or indirectly) and nor does passive diffusion. Both rely on diffusion, which is the tendency of molecules to spread out and their concentrations throughout a solution to equilibrate. Facilitated diffusion is passive diffusion through a protein channel, and it helps very polar molecules cross the hydrophobic plasma membrane core.

True or false: The structural backbone of all amino acids contains two carbon atoms and a nitrogen atom.

true. The structural backbone of an amino acid includes an amine group (-NH2), a central alpha carbon, and a carboxylic acid group (-COOH).