Chapters 1,2,3,4,11 reading quiz

The rules of which fundamental process were elucidated in the bacterium Escherichia coli (E. coli)? Correct!

DNA replication Feedback;The rules behind the process of DNA replication (as well as transcription and translation) were determined by experiments with the bacterial model organism E. coli. These simple prokaryotes are single-celled and do not have a cell cycle or mitosis, thus are best for studies of the most evolutionarily conserved cell processes.

Which way do the fatty acid tails of a phospholipid face in a cell membrane?

both directions FEEDBACK: To form cell membranes, phospholipids form a bilayer, with the fatty acid tails facing each other. Thus, one layer has the fatty acid tails facing inward and the other layer has the fatty acid tails facing outward.

All amino acids have which of the following chemical groups in common?

carboxyl group FEEDBACK: All amino acids have an amino group (NH2) and a carboxyl group (−COOH) attached to a central carbon. They differ in which side groups are attached to the central carbon, such as a methyl group or aromatic rings, for example.

The defiining property that differentiates prokaryotic cells from eukaryotic cells is their

lack of a nucleus Feedback:Prokaryotes are small, single-celled organisms with a simple cell structure and no membrane-bound organelles. There is no nucleus surrounding the DNA of prokaryotic cells.

Glucose has a molecular weight of 180 grams per mole. To prepare 1 liter of a 100 mM solution, how many grams of glucose would you dissolve in water for a total volume of 1 liter?

18 Glucose has a molecular weight of 180 g/mole, which means that dissolving this mass of glucose in a liter would give a 1 M solution. Because 100 mM is 0.1 M, it is 1/10 of the concentration. Using 1/10 of the molecular weight (18 g) in the same volume would give a 1/10 concentration, thus a 0.1 M or 100 mM solution.

How many bonds are made by a carbon atom?

4 Feedback:Carbon has four electrons in its outer shell and it needs eight to fill it. To fill its outer shell, carbon can share electrons with four different atoms, forming four bonds.

Given the periodic table below, how many electrons does an oxygen atom have?

8 FEEDBACK: The atomic number is the number of protons in the nucleus of an atom. For an atom to remain electrically neutral, the number of electrons is equal to the number of protons. Thus oxygen, with an atomic number of 8, has 8 electrons.

In the following condensation reaction, how does ATP power the formation of product A-B?

A phosphate is first transferred to reactant A−OH to form a high energy intermediate. FEEDBACK: ATP powers the formation of energetically unfavorable bonds between two molecules by first breaking its own high-energy phosphoanhydride bond and transferring the phosphate to another molecule. This new phosphate linkage can then be broken to power the bond formation between molecules.

Which of the following is a role of the cytoskeleton in plant cells?

Microtubules form tracks for movement of cell components. Feedback:While plant cells are immobile, actin filaments and microtubules still play a major role in the movement of organelles and cell components within the cell. Intermediate filaments are not found in the cytoplasm of plant cells.

Which of the following has a higher concentration in the cell to allow it to be available to accept electrons from oxidation of food molecules?

NAD+ FEEDBACK: Cells maintain high concentrations of NAD+ so that it is readily available to accept electrons from the oxidation of food molecules in catabolic reactio

For the following uncatalyzed reaction at equilibrium, how would the reaction change if it was now an enzyme-catalyzed reaction at equilibrium?

Forward reaction A would increase. FEEDBACK: Enzymes lower the activation energy for reactions and thus increase the probability that the energy barrier can be surpassed for the reaction to proceed. They do not change the equilibrium point (the relative levels of reactants and product at equilibrium).

(Q011) ________ are the most abundant molecules in the animal cell membrane, whereas ________ make up 50% of the membrane by mass.

Lipids, proteins FEEDBACK: Lipids are the most abundant molecule in the cell membrane. Proteins, however, are much more massive and thus, by mass, make up about 50% of the mass of the plasma membrane.

Why is the oxidation of NADPH energetically favorable? Correct!

The oxidized form of NADPH is more stable than the reduced form. FEEDBACK: NADPH carries two high-energy electrons. Losing these electrons in an oxidation reaction is energetically favorable because the oxidized form, NADP+, is more stable than the reduced form (NADPH).

What is the role of activated carriers in cells?

They capture energy from energy releasing reactions and transfer it to other reactions. FEEDBACK: Activated carriers collect electrons from oxidation of molecules in catabolic reactions and transfer them to anabolic reactions that require electrons for the reduction of molecules.

Which of the following is UNLIKELY to be hydrophilic?

a molecule with primarily nonpolar covalent bonds FEEDBACK: Hydrophilic molecules carry positive or negative charges, allowing them to interact with the partial charges on water molecules. Polar covalent bonds form partial charges, whereas nonpolar covalent bonds do not.

Which of the following is true about amyloid protein structures?

They consist of stacked β sheets. FEEDBACK: Amyloid protein structures are β sheets that interlock with each other through their side chains and form stacks. Since they are made from many β sheets, they form strong structures that have many roles in the cell, including formation of important cellular compartments. However, some amyloid structures, but not all, are abnormal and cause disease.

(Q017) Detergent molecules are ___________ in nature and bind with membrane proteins and membrane lipids to disrupt their interactions and release the proteins from the membrane.

amphipathic FEEDBACK: Detergents have a hydrophobic portion that disrupts the hydrophobic interaction of lipids with membrane proteins. They also have a hydrophilic region that stabilizes the protein in solution by interacting with the aqueous environment.

Reactions that build larger molecules in the cell are called ___________; reactions that break down molecules into smaller ones are called ___________.

anabolic; catabolic FEEDBACK: Metabolism is the sum total reactions in a cell, which are of two types. Catabolic reactions are the reactions where cells break down the large molecules in foodstuffs into their constituent building blocks. Anabolic reactions are biosynthetic—they build larger molecules from smaller building blocks.

The genes in the genome of an adult organism

are expressed or silenced depedning on whether a gene is needed in that cell type anf environement Feedback: the cells of an adult organism can be quote varied in their structure and function despite having the same information in their genome. Not all gene in the genome are expressed at all times, or in all cell types; some genes are exdpressed for specific purposs and might be uniqure for a particular type of cell or situation

Long polymers are made from single subunits in cells using a ___________ reaction, which ___________ water.

condensation; releases FEEDBACK: A condensation reaction joins two monomers together, releasing water. A hydrolysis reaction uses water to split the bond that joins two subunits of a polymer.

How does phosphorylation of a protein affect its activity?

could increase or decrease activity FEEDBACK: Phosphorylation of amino acid side chains in a protein changes their charge to a negative charge. It could lead to changes in conformation of the protein, differences in binding to partners, and either increased or decreased activity of an enzyme. Thus, the effects of protein phosphorylation are particular to the protein itself.

What is a protein family?

a structurally related group of proteins FEEDBACK: A protein family is a set of proteins that have similar primary structures (amino acid sequences) and thus have related three-dimensional structures. If the structure of one member of a protein family is determined, it can be used to make predictions about the structure of other members of the protein family.

A base is a molecule that will ___________ a proton in water.

accept FEEDBACK: Bases accept protons in water, removing a proton from a water molecule, forming OH?2_ ions. If the hydrogen atoms in water are more attracted to the electronegative atom of a base, they can be stripped off as a proton.

Amino acids with side chains that contain −COOH groups, like those shown below, would be ___________ in the aqueous environment of a cell.

acidic FEEDBACK: Amino acids like glutamic acid and aspartic acid have side chains that terminate in carboxylic acid groups (−COOH). This group loses a proton in water and is acidic in nature.

Which method is used for separating proteins based on specific interactions with other molecules?

affinity chromatography FEEDBACK: Affinity chromatography separates proteins from one another by using a known molecular interaction with the protein of interest. Gel electrophoresis and mass spectrometry separate protein fragments by size and charge. X-ray crystallography is a method for determining the three-dimensional structure of a protein; it is not used for separation.

How does binding of GTP to a GTP-binding protein affect its activity?

always activates the protein FEEDBACK: Proteins in the GTP-binding protein family are always in their active conformation when GTP is bound, in contrast to phosphorylation of a protein, which can activate or inactivate a protein. The hydrolysis of GTP to GDP returns the protein to the inactive state.

Which of the following occurs by bringing nonpolar surfaces together to exclude water?

hydrophobic forces FEEDBACK: Surfaces with nonpolar bonds cannot favorably interact with water. These hydrophobic surfaces prefer to come together to exclude water. This is referred to as hydrophobic force.

(Q002) Phospholipids assemble into in a membrane using

hydrophobic forces. FEEDBACK: Because phospholipids have a polar head group and a nonpolar fatty acid tail, the hydrophobic nature of the tails will drive them together into a structure that excludes water from the tail group. This drives the spontaneous formation of closed vesicles and membrane bilayers.

If a reaction is energetically favorable (exergonic), then it must produce a(n)

increase in entropy. FEEDBACK: Reactions that are energetically favorable increase the entropy (or disorder) of the universe. This can be through either the release of free energy in different forms, or the release of energy as heat (energy in its most disordered form).

Enzymes increase the speed of a chemical reaction because they

lower the activation energy needed to start the reaction. FEEDBACK: Enzymes work by lowering the threshold energy input, called the activation energy, needed to start a reaction.

The fruit fly, Drosophila melanogaster (D. melanogaster) is an excellent model for studying fundamentals of development because

many of the genes involved in the development of the fruit fly are also found in humans. FEEDBACK: Fruit flies have been studied for over a century, and their complex body plan can be manipulated genetically to uncover which genes govern development of which parts. Many of these genes have direct counterparts in the human genome.

Strong and specific associations between macromolecules or between an enzyme and its substrate are due to

many weak noncovalent bonds. FEEDBACK: Two macromolecules in a cell come together in a very specific way through many weak noncovalent associations between them. This allows more specificity, but also easier reversibility, as molecular interactions often must be relatively short lived in cells.

If the products of a reaction have more free energy than the reactants, then that reaction is

not energetically favorable. FEEDBACK: Reactions that have products with LESS free energy than the reactants will release free energy and create more disorder in the system. These will proceed spontaneously and are energetically favorable. However, when products of a reaction have MORE free energy than the reactants, there is no release of energy, and the reaction is not energetically favorable.

(Q001) Which of these macromolecules is NOT commonly found in the plasma membrane?

nucleic acids FEEDBACK: The plasma membrane is primarily made up of a lipid bilayer with the fatty acid tails facing each other, and membrane proteins are also found throughout the membrane. Both membrane lipids and proteins are frequently modified with carbohydrate groups to form glycolipids and glycoproteins.

(Q014) Proteins that are associated with the membrane by noncovalent interactions with other membrane proteins are called ___________ proteins.

peripheral membrane FEEDBACK: A protein that is associated with the membrane simply by virtue of interacting with another membrane protein are called peripheral membrane proteins. On the other hand, transmembrane, monolayer associated, and lipid-linked proteins are all directly associated with the membrane and are called integral membrane proteins.

A stretch of amino acids in a polypeptide chain that is capable of independently folding into a defined structure is called a

domain FEEDBACK: A domain is a sequence of amino acids in a polypeptide chain that adopts a defined folding pattern based on the interactions of the side chains, as well as contributions from the polypeptide backbone molecules. This is distinct from a subunit, which is a term used for a single, complete polypeptide chain that can interact with other subunits to form a larger complex.

Which of the following shows protein organizational units in the correct order from smallest to largest?

domain < subunit < complex FEEDBACK: A domain is a portion of an amino acid sequence that folds into a three-dimensional structure and is the smallest of the organizational units. A subunit is a single, complete polypeptide chain and may be made up of one or more domains. Two or more subunits can assemble into a complex.

What purpose does NADPH serve in biosynthetic reactions like the one pictured below?

donating electrons for a reduction reaction FEEDBACK: NADPH is a carrier of electrons that are used in reduction reactions often used in biosynthesis of molecules. In the process, NADPH donates electrons, and itself becomes oxidized to NADP+.

(Q008) Where are new phospholipids made?

endoplasmic reticulum FEEDBACK: Enzymes that are bound to the cytosolic face of the ER membrane make new phospholipids and insert them into the ER membrane.

The organelle shown in the figure is the _ and one of its main functions is to _

gologi apparatus; package and modify proteins for secretion feedback; The Golgi apparatus is a series of flattened sacs that receives proteins from the ER. It modifies and prepares these proteins for secretion outside of the cell.

Living systems can generate and maintain order without violating the second law of thermodynamics because they generate

heat FEEDBACK: Even though living systems produce ordered structures from smaller building blocks, this does not violate the second law of thermodynamics because they still create disorder by releasing energy in the form of heat. Heat is energy in its most disordered form.

Biochemical subcompartments that form inside the nucleus are distinct from their immediate surroundings because of the

high concentrations of interacting proteins and RNA. FEEDBACK: Biochemical subcompartments can form inside of organelles by the aggregation of interacting proteins, RNA, and protein complexes that perform a concerted function. These "intracellular condensates" are simply concentrations of molecules; they are not bound by a membrane, nor are they hydrophobic droplets.

If a gene sequence in one organism is highly similar to the sequence of another gene in another organism it is called Correct!

homologous Feedback:Gene sequences from one organism can be compared to another organism to see if they are homologous. Homology between genes (and thus also their protein products) strongly suggests that they evolved from a common ancestral gene.

The main function of the nucleus is to

house the DNA in a separate cell compartment Feedback:DNA, in the form of chromosomes, is stored in the nucleus. Keeping the DNA separate from other cell components helps eukaryotic cells regulate access to the genetic information.

Which type of noncovalent interaction can involve either the polypeptide backbone or amino acid side chains?

hydrogen bonds FEEDBACK: The backbone of the polypeptide consists of uncharged polar covalent bonds. Because the bonds in the backbone are neither charger nor hydrophobic (i.e. nonpolar), hydrophobic forces and electrostatic interactions do not involve the backbone. Hydrogen bonds, however, are formed between atoms in the polar covalent bonds found in both amino acid side chains and in the carboxyl group and amino groups of the polypeptide backbone.

Lysosomes and peroxisomes both perform a series of reactions to break down molecules, but one difference between them is that

peroxisomes contain hydrogen peroxide Feedback:Both peroxisomes and lysosomes are small organelles that break down materials, but lysosomes generally digest biomolecules like proteins so that the building blocks can be reused. Peroxisomes deactivate toxic materials, often using hydrogen peroxide.

A nucleotide is different from a nucleoside because a nucleotide has a

phosphate group(s). FEEDBACK: A nucleotide is a sugar (either ribose or deoxyribose), attached to a nitrogen-containing base, and one or more phosphate groups. A nucleoside simply lacks any phosphate groups.

A readily available source of energy that cells use to drive reactions is stored in the ___________ bond.

phosphoanhydride FEEDBACK: Nucleotide triphosphates, notably ATP, have three phosphoanhydride which can be hydrolyzed easily to release energy.

What is the name used for a molecule in which two carbons of glycerol are attached to fatty acid chains, and the third carbon is attached to a phosphate group?

phospholipid FEEDBACK: Glycerol molecules have three carbons attached to −OH groups that can be linked to fatty acids or other molecules. When two fatty acids and a phosphate are attached to glycerol, it is called a phospholipid. If three fatty acids are attached, it is called a triacylglycerol.

(Q003) What kind of lipid molecule is represented in this figure?

phospholipid FEEDBACK: Phospholipids, glycolipids, and triacylglycerol all consist of a 3-carbon glycerol molecule with fatty acids attached to two of its carbons. The molecule attached to the third carbon differs between the three lipid categories: in triacylglycerol it is another fatty acid, in glycolipids it is a sugar molecule, in phospholipids it is a phosphate.

(Q020) Which of the following is NOT a way that cells restrict the lateral movement of membrane proteins?

reducing the temperature of the membrane FEEDBACK: Cells restrict lateral movement of membrane proteins by tethering them to internal or external components, or by creating barriers to their movement. Temperature changes are not a way that protein movement is regulated by the cell.

In an enzymatic reaction, a molecule gains an electron. This is known as a(n) ___________ reaction.

reduction FEEDBACK: Gain of electrons by a molecule is called reduction; loss of electrons is called oxidation.

Which of the following is an inorganic compound?

table salt (e.g., NaCl) FEEDBACK: Organic compounds are made up of carbon atoms linked together, frequently along with other atoms and chemical groups. Inorganic compounds do not contain multiple linked carbon atoms.

One piece of evidence indicating that chloroplasta evolved from engulfed photosynthetic bacteria is

that they contain their own dna Feedback:Chloroplasts, like mitochondria, contain their own DNA and reproduce by dividing in two. Both are thought to have evolved by symbiotic engulfed bacterial cells, but in two separate engulfment events.

Archar and bacteria are two seperate domains of prokaryotes that were distinguised by examing

their DNA sequence Feedback:Archaea and bacteria are similar in size and cell appearance under a microscope, but they differ significantly in their genome sequences. Because they are both prokaryotes, they lack a nucleus and any organelles.

(Q007) Why do cells regulate their membrane fluidity?

to allow membrane proteins to diffuse to where they are needed for their function FEEDBACK: Membrane fluidity can be regulated by cells by changing the lipid composition of the membrane. This is important for allowing proteins to move within the membrane, from their place of insertion to the location where they function. In addition, membrane proteins have to come into contact other proteins for signaling.

The cell components that move materials from one organelle to another are called

transport vesicles feedback:Transport vesicles are small membrane-bound compartments that bud off of one organelle, move to another organelle and fuse with it to release its contents into the interior.

(Q012) Plasma membrane proteins that move ions in and out of cells using active transport are called

transporters. FEEDBACK: Transporters move ions using active transport. Channels allow cells to move in and out of cells down their concentration gradient.

The function of feedback inhibition of an enzymatic pathway is to

turn off synthesis of a product when it is in abundance. FEEDBACK: Feedback inhibition keeps the cell from accumulating unnecessarily large amounts of biological compounds by reversibly inhibiting an enzyme in the biosynthetic pathway for that compound. These mechanisms shut down the enzymes early in the pathway so that wasteful intermediates do not accumulate.

The technique that scientists used to determine that hemoglobin was a single large macromolecule rather than a loose conglomeration of small organic molecules was

ultracentrifugation. FEEDBACK: Scientists at first did not believe that molecules could be as large as hemoglobin, and thought they were a lot of smaller molecules held together in close association. Separating molecules by size in ultracentrifugation allowed scientists to see if macromolecules were just one molecule of a large size, or many small molecules.

Condensation reactions are energetically ___________ and hydrolysis reactions are energetically ___________.

unfavorable; favorable FEEDBACK: Condensation reactions reduce the disorder in the universe and are energetically unfavorable. Hydrolysis reactions increase the disorder in the universe and are energetically favorable.

A folded protein structure with which free-energy (G) value would likely have the most stable conformation?

1 FEEDBACK: Free energy is designated by the letter G. If the free-energy value decreases during protein folding, the reaction is energetically favorable. Proteins generally fold along the most energetically favorable pathway, so the conformation with the lowest free-energy (G) value, 1, is the correct answer.

The figure below shows a depiction of an antibody. Which label correctly identifies the region(s) of the antibody that contains variable amino acids for binding of a specific antigen?

A FEEDBACK: Unique antigen-binding sites in antibodies are formed by varying the terminal amino acid sequences in the heavy chain and the light chain, which come together into a unique three-dimensional conformation for specific side-chain interactions with the antigen. Since each antibody is made up of two heavy chains and two light chains, there are two antigen-binding sites per antibody.

If protein folding is determined by the sequence of amino acids in the polypeptide chain, why are chaperone proteins needed to assist folding in the cell?

Certain proteins easily aggregate with other proteins. FEEDBACK: All proteins can fold on their own without assistance due to the energetically favorable interactions between amino acid side chains and/or the polypeptide backbone. However, the cytoplasm is crowded and some proteins can form favorable interactions with other proteins before they have a chance to fold. These aggregates could impede proper folding.

Which of the following is INCORRECT regarding how enzymes lower the activation energy of a reaction?

Enzymes reduce the free energy of the products of the reaction. FEEDBACK: Enzymes lower activation energy of a reaction by promoting changes in the substrate that will encourage the reaction to occur. This can include changes in shape, alignment of two substrates, or changes in the electron density to encourage bond breakage and formation. Enzymes do not change the overall free energy of the reaction.

(Q013) How is the protein shown in the diagram associated with the plasma membrane?

It is associated with one layer of the lipid bilayer. FEEDBACK: Proteins can be directly associated with the membrane by being fully inserted into the membrane (transmembrane) or they can be inserted into one of the layers of the bilayer (monolayer associated). The protein shown has one alpha helix that interacts with one face of the lipid bilayer, making it monolayer associated.

Genome size does not precisely determine gene number, as illustrated in the table below. What is a plausible explanation as to why A. thaliana, a plant, has a similarly sized genome as the fruit fly, but twice the number of protein-coding genes?

Plants have more genes that were duplicated during evolution. Feedback:Plants have genes that were duplicated during evolution, and thus their protein-coding gene number is higher. Repeated noncoding sequences cannot explain this observation, since these do not get counted in the number of protein-coding genes.

(Q019) In a fluorescence recovery after photobleaching (FRAP) experiment, a fluorescently tagged membrane protein, A, shows very little recovery of fluorescence ten minutes after photobleaching, while membrane protein B shows a rapid increase in fluorescence after bleaching, recovering nearly 80% of its original fluorescent signal by ten minutes. Based on this information, which of the following statements can be made?

Protein B is diffusing in a more fluid membrane. FEEDBACK: The recovery of fluorescence in FRAP experiments is directly related to the amount of mobility the protein exhibits. This can be due to increased fluidity of the membrane, as well as whether the protein is relatively unconstrained by interactions that would impede on its motion.

What is one of the main differences between DNA and RNA?

RNA has two hydroxyl groups on the sugar, DNA has one FEEDBACK: RNA uses the sugar ribose, which has a 2′ and a 3′ −OH, whereas DNA uses the sugar deoxyribose, which only has a 2′ −OH. This leads to fundamental differences in the self-replication and stability of these molecules.

For a reaction Y à X with a very high equilibrium constant, K, which of the following is true? You can refer to the following two equations in formulating your answer.ΔG = ΔG° + RT ln

The amount of product will be higher than the amount of substrate at equilibrium. FEEDBACK: If the equilibrium constant, K, is very high, it means that there is far more of the product X than substrate Y at equilibrium (i.e., when forward and reverse reaction rates are balanced). This corresponds to a free-energy change that is large and negative.

Shown below is the ATP hydrolysis cycle of a motor protein. What sentence BEST describes the state of the motor protein in "C"?

The hydrolysis of ATP to ADP caused a conformational change in the protein. FEEDBACK: (A) is the state where no ATP or ADP is bound. The protein is bound to the filament with one of its two filament-binding domains, while the other binding domain is unbound. (B) shows that upon ATP binding, a conformational change moves the unbound domain forward one step to interact with the filament. In (C), ATP is hydrolyzed to ADP, creating a conformational change to release the rear filament-binding domain and bring it forward.

(Q018) In a famous experiment, mouse cells and human cells were fused into hybrid cells and the membrane proteins of human origin and mouse origin were specifically tagged and examined. After cell fusion and incubation, what was observed by investigators?

The mouse and human proteins mixed evenly throughout the membrane of the hybrid cell. FEEDBACK: In the 1970s investigators made mouse-human cell hybrids by fusing cells together and tracked the location of human membrane proteins and mouse membrane proteins. The proteins evenly mixed throughout the membrane over time, demonstrating the mobility of the proteins in the lipid bilayer.

Which of the following is a reason why ATP hydrolysis has a negative ΔG0?

The removal of the phosphate is energetically favorable. FEEDBACK: The products of the ATP hydrolysis reaction—ADP and free phosphate—are more stable and have a lower free energy. Release of free phosphate is energetically favorable because it relieves the repulsion of the negative charges of the neighboring phosphate groups and the aqueous environment to make hydrogen bonds with the phosphate.

A molecule with a lot of polar covalent bonds is likely to

be highly soluble in water. FEEDBACK: Polar covalent bonds are formed when two atoms unequally share an electron, forming partial positive and partial negative charges at either end of the bond. Water also has partial positive and negative charges, and thus will easily interact with other molecules' partial charges, thus making it soluble.

(Q015) If the backbone of a polypeptide is hydrophilic, how can a transmembrane alpha helix span the hydrophobic portion of the lipid bilayer?

because amino acid side chains in a transmembrane helix are hydrophobic and interact with the hydrophobic interior of the bilayer FEEDBACK: Although the backbone is hydrophilic, the amino acid side chains of an alpha helix stick out from the helix. If those amino acid side chains are hydrophobic, they will interact with the hydrophobic tails in the bilayer and shield the hydrophilic backbone from unfavorable interactions.

Why is CO2 an end product of cellular respiration? Correct!

because it is the most stable form of carbon in our atmosphere FEEDBACK: Cellular respiration is the breakdown of carbon-containing molecules through oxidation to release energy. Because the most energetically stable form of carbon in the presence of oxygen is carbon dioxide, this is the final end product of respiration.

Why is sunlight the ultimate source of energy for nearly all living things on Earth?

because photosynthetic organisms produce food molecules using light energy FEEDBACK: Organic molecules for energy are obtained by animals through their diet, by consuming either plants or animals that eat plants. Plants produce organic molecules using energy from the sun, thus the source of energy from food molecules in plants is ultimately from the sun.

(Q016) Which of the following is a common transmembrane protein structure that can traverse the membrane to form a pore or channel by alternating hydrophobic and hydrophilic amino acids?

beta barrel FEEDBACK: A beta barrel is a beta sheet structure that is rolled into a cylinder. In beta sheets, the amino acid side chains protrude out from the sheet in an alternating fashion from one side of the sheet to another. For a beta barrel to form a transmembrane pore, the side chains facing the lipid bilayer must be hydrophobic, while the adjacent side chains, which face the aqueous pore, must be hydrophilic.

The chemical reactions that take place in a cell, as compared to the chemistry in nonliving matter, primarily occur

between carbon-based molecules. FEEDBACK: The chemistry of living things follows all the same chemical and physical laws of the chemistry that occurs in the nonliving world. The difference is that the chemical compounds of life are mostly carbon-based polymers that undergo complex reactions in an aqueous environment.

A segment of DNA in the genome that is not a protein-coding gene

can be used to regulate gene activity. Feedback:The genome of a complex organism is made up of protein-coding genes, sequences that encode functional RNAs, and regulatory sequences used to finely tune gene activity. Other DNA noncoding sequences seem to be unimportant to the cell, but we might just not understand their function yet.

Mistakes in replicating the DNA of a cell before division

can have positive, negative, or neutral effects Feedback: mistakes in the DNA sequence depending on where they oocur, can have positive, negative, or neutral effects on cell growth survival. CHanes that have positiv eeffects on survival and reproduction can lead to the enrichment, called selection, of cells, with that change in the population.

Disulfide bonds stabilize protein shape outside the cell by

covalent bonds between cysteines. FEEDBACK: Using mechanisms such as noncovalent bonds between charged side chains, proteins fold into their final conformation based on their amino acid sequence inside the cell. However, in the harsh environment outside the cell, this structure needs to be stabilized to keep its final form and function. Disulfide bonds are covalent cross-linkages between cysteine groups juxtaposed in the three-dimensional structure, and they act to hold the shape of the protein.

Which method is most suitable for determining the three-dimensional structure of an extremely large integral membrane protein complex?

cryoelectron microscopy FEEDBACK: Large proteins produce confounding signals on NMR spectra, and large integral membrane complexes are hard to crystallize for x-ray crystallography. Structural studies of large integral membrane protein complex could be performed with cryoelectron microscopy. In this method, the purified protein complex is embedded in ice and a beam of electrons is used to collect projected images in multiple orientations.

Which cell component is indicated in the figure below the line labeled "1"?

cytosol FEEDBACK: The cytosol is an aqueous solution of soluble proteins and other macromolecules. It is the part of the cytoplasm that is not contained within organelles.

(Q004) Which type of movement is the least common for lipids in a bilayer?

flip-flop FEEDBACK: Lipids rarely flip-flop between the different faces of the bilayer because the polar heads would have to contact the hydrophobic interior of the membrane. This only happens when catalyzed by transporter proteins.

which of the following microscopy techniques allows the observation of living cells (i.e. NOT fixed cells)?

fluorence microscopy Feedback:Light microscopy, which also includes fluorescence microscopy, can be used to view living cells. Electron microscopy requires cell fixation and extensive preparation of the samples, which kills the cells.

The inner membrane of the mitochondrion appears _ because it provides _

folded, a large surface area for staging energy production processes Feedback:In mitochondria, the outer membrane is smooth, while the inner membrane is highly folded and convoluted. The proteins that are responsible for energy production via respiration are found in the inner membrane.

Which of the following is a role that sugars can play outside of their role in energy production and storage?

formation of support structures FEEDBACK: Sugars play many roles outside of being an energy source that is stored and/or harvested for powering cellular processes. Sugars also form support structures like cell walls, exoskeletons, or adherent structures on the cell surface.

When a ligand binds to an allosteric enzyme's regulatory site, it changes the activity of that enzyme by

inducing a conformational change. FEEDBACK: Once a regulatory molecule or ligand binds to a regulatory site, an allosteric protein undergoes a conformational change that is transmitted to the active site. Inducing the conformational change can change the activity of the enzyme, but it does NOT directly block the active site.

Covalent bonds in macromolecules are primarily important for Correct!

linking together monomers. FEEDBACK: Covalent bonds are strong and are used within molecules to form the linkages between monomers that form the polymer. Noncovalent bonds are more important for the three-dimensional conformation and for interactions with other molecules.

(Q005) A cell membrane made up primarily of lipids with which characteristics would be the least fluid (i.e., most stiff)?

long, saturated fatty acid tails FEEDBACK: The longer the fatty acid tail, the more tendency for interaction between the tails, which reduces the fluidity of the membrane. In addition, the more closely packed the fatty acid tails, the less fluid the membrane; saturated fatty acid tails have no double bonds and can pack more closely together.

A binding site on the surface of a protein interacts specifically with another protein through Correct!

many weak noncovalent interactions. FEEDBACK: Covalent interactions are rarely used between protein molecules because they are difficult to break, often requiring an enzyme. Interactions between proteins and their partners need to be reversible but very specific. A specific interaction, but one that is able to be altered, can be achieved through formation of many weak noncovalent interactions between proteins and their binding partners.

Which of the following chemical groups could confer nonpolar/hydrophobic characteristics on the region of a molecule in which it is found?

methyl group (−CH3) FEEDBACK: Bonds between carbon and hydrogen are nonpolar and molecules with mostly nonpolar bonds are hydrophobic. Bonds between H and electronegative atoms like O and N are polar and tend to impart hydrophilic characteristics.

Which of the following accurately matches the type of filaments in the cytoskeleton with their cellular function?

microtubules-chromosomes segregation; intermediate filaments; strength/suport;actin filaments-cell movement Feedback:Microtubules form the mitotic spindle that functions in accurate chromosome segregation, intermediate filaments have a primary function of providing strength and support to the cell, and actin filaments are involved in dynamic processes such as cell motility.

Compared to eukaryotes, prokaryotic organims are

more abundant and more widespread on earth Feedback:Prokaryotic organisms are everywhere, and they live in a very wide range of habitats on Earth, including some of the harshest environments on the planet.

(Q006) A less permeable membrane is likely to have

more cholesterol. FEEDBACK: Lower permeability membranes have lower fluidity. Attributes that lead to lower permeability are: high amounts of cholesterol, more saturated fatty acids, and longer fatty acid tails.

The function of a(n) cell, which has a long, branched structure, required many connections to be made with neighboring cells.

nerve Feedback: nerve cells have long, branched protrusions that form many contacts with other cells. This allows communicaton between the nerve cells, and the sending of signals.

Cellular respiration ___________ energy and produces ___________, whereas photosynthesis ___________ energy and produces ___________.

produces; water + carbon dioxide; consumes; oxygen + sugars FEEDBACK: Cellular respiration is the process by which cells break down food molecules for energy, producing water and carbon dioxide as waste products. Photosynthesis uses energy from the sun to make food molecules (sugars) and oxygen.

Self-replication of living cells occurs through the catalytic action of...

proteins Feedback: to self replicate, cells must first replicate their DNA, followed by division in two. DNA replication is performed by enzymes, which are proteins.

Which of the following levels of protein structure involves the interaction of more than one polypeptide chain into a three-dimensional structure?

quaternary FEEDBACK: Primary structure is the linear order of amino acids in a polypeptide chain. The secondary structure is the formation of organized arrangements to form segments like α helices and β sheets. The tertiary structure is the overall three-dimensional shape of a protein. The quaternary structure is the assembly of multiple folded polypeptide chains into a larger complex.

wo atoms held together solely by ionic bonds are referred to as a(n) Correct!

salt Feedback;Atoms are the simplest form of an element that still retain the properties of that element. When multiple atoms come together, it is called a molecule, but when those bonds are solely ionic bonds, it is often called a salt.

Which of the following microscopy techniques would allow the most detailed image showing the 3=D structure of a flagellun?

scanning electron microscopy Feedback: of all the microscopy tehcniques listed, electron microscopy provdies the most high resolution and detailed images. Scanning electron microscopy examines the outer surface of the cell structure and gives a 3-d image

(Q009) A phospholipid is inserted into the cytosolic side of the ER membrane. Which of the following could randomly reposition this phospholipid to the other (lumen) side of the ER membrane?

scramblase FEEDBACK: Scramblase is an enzyme that randomly mixes phospholipids from one face of the ER membrane to the other. Flippases selectively move phospholipids from one face to another.

All living cells...

share the same basic chemistry Feedback: living cells are remarkablly diverse in size and shape but are governed by the same chemical principles.

Chemical modifications like phosphorylation and acetylation of proteins occur on ___________ of amino acids and can affect interaction of proteins with other cell components or structures.

side chains FEEDBACK: The chemical modification of phosphorylation and acetylation occurs on the side chain of the amino acid and can affect how proteins interact with other proteins or components of the cell. This effect can occur through the direct alteration of binding sites if the phosphorylation and acetylation occur on an amino acid in a binding site, or through a conformational change that indirectly alters the binding site.

The Michaelis constant (KM) of an enzyme is a measure of

the binding strength of enzyme to substrate. FEEDBACK: Enzyme activity is measured using two values. The first is the rate at which the enzyme converts the substrate to product, which is called Vmax. This value is determined by measuring the rate of product formation in conditions where all enzyme binding sites are occupied by substrate. The Michaelis constant measures the relative binding strength of the enzyme to substrate, determined by the concentration of substrate at which the enzyme operates at half of its Vmax.

(Q010) If a phospholipid is located in the outer layer of the bilayer in a vesicle, where will it end up when the vesicle fuses with the plasma membrane?

the cytosolic face of the bilayer FEEDBACK: When a vesicle fuses with the plasma membrane, the lipids on the outside of the vesicle will end up in the phospholipid layer on the inside (cytosolic face) of the plasma membrane. Lipids on the inside of the vesicle membrane will face the extracellular fluid in the plasma membrane.

The following image shows two triacylglycerol molecules with different fatty acid chains. If these fatty acids were in a phospholipid molecule, which of the two would form the most fluid membrane?

unsaturated FEEDBACK: Unsaturated fatty acids have double bonds in their hydrocarbon chains, and so have kinks in them; these keep them further apart. Thus, membranes made from unsaturated fatty acids are more fluid because they cannot pack as closely together as saturated fatty acids, which have no double bonds and are straighter.

Ionic bonds are ___________ than covalent bonds and are ___________ common in cells.

weaker; less FEEDBACK: Ionic bonds are weak bonds commonly found in salts that form ions in aqueous solution. Because the cell environment is primarily aqueous, ionic bonds are dissociated by interaction with water.

What is the value of ΔG at equilibrium?

zero FEEDBACK: When equilibrium is reached, the forward and reverse reactions are equal, so there is no net change in the number of reactants and products. The reaction does not proceed forward or backward at this point and ΔG is equal to zero.

What is the relationship between ΔG and ΔG0?

ΔG0 is the free-energy change at standard temperature and concentrations. FEEDBACK: The value of the free-energy change of a reaction, ΔG, is dependent upon the concentration of reactants and products, as well as the temperature of the system. ΔG0 is the standard free-energy change at standard temperature and concentrations to allow comparison of different reactions.

Hydrogen bonding between N-H and C=O groups of every fourth amino acid within a polypeptide chain results in which type of folding pattern?

α helix (D) FEEDBACK: The hydrogen bonds that form a β-pleated sheet structure occur between the N-H and C=O groups of amino acids in different segments of a single polypeptide chain lying side by side. Amyloid structures are β sheets that interlock with each other through their side chains. The α helices are formed by hydrogen bonds between every fourth amino acid in the primary structure.