Chapter 3 biology cell

3-13 During respiration, energy is retrieved from the high-energy bonds found in certain organic molecules. Which of the following, in addition to energy, are the ultimate products of respiration? (a) CO2, H2O (b) CH3, H2O (c) CH2OH, O2 (d) CO2, O2

A

3-15 Oxidation is a favorable process in an aerobic environment, which is the reason cells are able to derive energy from the oxidation of macromolecules. Once carbon has been oxidized to _______________, its most stable form, it can only cycle back into the organic portion of the carbon cycle through __________________. (a) CO2, photosynthesis. (b) CH3, combustion. (c) CO2, respiration. (d) CO, reduction.

A

3-34 For the reaction YàX at standard conditions with [Y] = 1 M and [X] = 1 M, ΔG is initially a large negative number. As the reaction proceeds, [Y] decreases and [X] increases until the system reaches equilibrium. How do the values of ΔG and ΔG° change as the reaction equilibrates? (a) ΔG becomes less negative and ΔG° stays the same. (b) ΔG becomes positive and ΔG° becomes positive. (c) ΔG stays the same and ΔG° becomes less negative. (d) ΔG reaches zero and ΔG° becomes more negative.

A

3-38 Isomerization of glucose 1-phosphate to glucose 6-phosphate is energetically favorable. At 37°C, ΔG° = -1.42 log10K. What is the equilibrium constant for this reaction if ΔG° = -1.74 kcal/mole at 37°C? (a) 16.98 (b) 0.09 (c) -0.09 (d) 0.39

A

3-50 The net distance a molecule travels through the cytosol via diffusion is relatively short in comparison with the total distance it may need to travel. This is because movement governed by diffusion alone is a ________________ process that is most effective for the dispersion of small molecules over short distances. (a) slow (b) random (c) regulated (d) complicated

A

3-62 What information regarding an enzyme-catalyzed reaction is obtained in a plot of the inverse of the initial velocities against the inverse of the corresponding substrate concentrations? (a) 1/Vmax and 1/Km (b) 1/V and 1/[S] (c) Vmax and Km (d) V and [S]

A

3-64 The study of enzymes also includes an examination of how the activity is regulated. Molecules that can act as competitive inhibitors for a specific reaction are often similar in shape and size to the enzyme's substrate. Which variable(s) used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor? (a) Vmax (b) V (c) Vmax and Km (d) Km

A

3-71 The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-71. Which molecule is added to glutamic acid in the activation step? (a) phosphate (b) NH3 (c) ATP (d) ADP

A

3-11 In the first stage of photosynthesis, light energy is converted into what other form of energy? (a) electrical (b) chemical (c) potential (d) kinetic

A or D

3-61 The maximum velocity (Vmax) of an enzymatic reaction is an important piece of information regarding how the enzyme works. What series of measurements can be taken in order to infer the maximum velocity of an enzyme-catalyzed reaction? (a) the rate of substrate consumption after the system reaches equilibrium, for several reactant concentrations (b) the rate of product consumption shortly after mixing the enzyme and substrate (c) the rate of substrate consumption at high levels of enzyme concentration (d) the rate of substrate consumption shortly after mixing the enzyme and substrate, for several substrate concentrations

D

3-65 Activated carriers are small molecules that can diffuse rapidly and be used to drive biosynthetic reactions in the cell. Their energy is stored in a readily transferable form such as high-energy electrons or chemical groups. Which of the molecules below is the most widely used activated carrier? (a) FADH2 (b) NADH (c) NADPH (d) ATP

D

3-72 The synthesis of glutamine from glutamic acid requires the production of an activated intermediate followed by a condensation step that completes the process. Both amino acids are shown in Figure Q3-72.In the condensation step, _______________ is displaced by ________________. (a) OH, NH3. (b) ADP, NH2. (c) ATP, NH3. (d) phosphate, NH3.

D

3-73 NADH and NADPH are activated carrier molecules that function in completely different metabolic reactions. Both carry two additional ________ and one additional _____________. This combination can also be referred to as a hydride ion. (a) protons, electron. (b) electrons, phosphate. (c) hydrogens, electron. (d) electrons, proton.

D

3-47 The equilibrium constant for complex formation between molecules A and B will depend on their relative concentrations, as well as the rates at which the molecules associate and dissociate. The association rate will be larger than the dissociation rate when complex formation is favorable. The energy that drives this process is referred to as ___________. (a) dissociation energy. (b) association energy. (c) binding energy. (d) releasing energy.

C

3-5 At first glance, it may seem that living systems are able to defy the second law of thermodynamics. However, on closer examination, it becomes clear that although cells create organization from raw materials in the environment, they also contribute to disorder in the environment by releasing _____________. (a) water. (b) radiation. (c) heat. (d) proteins.

C

3-51 The small molecule cyclic AMP (cAMP) takes about 0.2 second to diffuse 10 μm, on average, in a cell. Suppose that cAMP is produced near the plasma membrane on one end of the cell; how long will it take for this cAMP to diffuse through the cytosol and reach the opposite end of a very large cell, on average? Assume that the cell is 200 μm in diameter. (a) 4 seconds (b) 16 seconds (c) 80 seconds (d) 200 seconds

C

3-52 The graph in Figure Q3-52 illustrates the relationship between reaction rates and substrate concentration for an enzyme-catalyzed reaction. What does the Km value indicate with respect to enzyme-substrate interactions? (a) the maximum rate of catalysis (b) the number of enzyme active sites (c) the enzyme-substrate binding affinity (d) the equilibrium rate of catalysis

C

3-53 The graph in Figure Q3-53 illustrates the change in the rate of an enzyme-catalyzed reaction as the concentration of substrate is increased. Which of the values listed below is used to calculate the enzyme turnover number? (a) 1⁄2Vmax (b) Km (c) Vmax (d) Vmax - Km

C

3-54 Protein E can bind to two different proteins, S and I. The binding reactions are described by the following equations and values: E + S->ES Keq for ES = 10 E + I->EI Keq for EI = 2 Given the equilibrium constant values, which one of the following statements is true? (a) E binds I more tightly than S. (b) When S is present in excess, no I molecules will bind to E. (c) The binding energy of the ES interaction is greater than that of the EI interaction. (d) Changing an amino acid on the binding surface of I from a basic amino acid to an acidic one will probably make the free energy of association with E more negative.

C

3-66 Energy cannot be created or destroyed, but it can be converted into other types of energy. Cells use potential kinetic energy to generate stored chemical energy in the form of activated carrier molecules, which are often employed to join two molecules together in _____________ reactions. (a) oxidation (b) hydrolysis (c) condensation (d) reduction

C

3-68 You are studying a biochemical pathway that requires ATP as an energy source. To your dismay, the reactions soon stop, partly because the ATP is rapidly used up and partly because an excess of ADP builds up and inhibits the enzymes involved. You are about to give up when the following table from a biochemistry textbook catches your eye. Figure Q3-68 Which of the following reagents are most likely to revitalize your reaction? (a) a vast excess of ATP (b) glucose 6-phosphate and enzyme D (c) creatine phosphate and enzyme A (d) pyrophosphate

C

3-69 The anhydride formed between a carboxylic acid and a phosphate (Figure Q3-69A) is a high-energy intermediate for some reactions in which ATP is the energy source. Arsenate can also be incorporated into a similar high-energy intermediate in place of the phosphate (Figure Q3-69B). Figure Q3-69C shows the reaction profiles for the hydrolysis of these two high-energy intermediates. What is the effect of substituting arsenate for phosphate in this reaction? (a) It forms a high-energy intermediate of lower energy. (b) It forms a high-energy intermediate of the same energy. (c) It decreases the stability of the high-energy intermediate. (d) It increases the stability of the high-energy intermediate.

C

3-1 Chemical reactions carried out by living systems depend on the ability of some organisms to capture and use atoms from nonliving sources in the environment. The specific subset of these reactions that break down nutrients in food can be described as _____________. (a) metabolic. (b) catabolic. (c) anabolic. (d) biosynthetic.

B

3-14 Your body extracts energy from the food you ingest by catalyzing reactions that essentially "burn" the food molecules in a stepwise fashion. What is another way to describe this process? (a) reduction (b) oxidation (c) dehydration (d) solvation

B

3-17 Oxidation is the process by which oxygen atoms are added to a target molecule. Generally, the atom that is oxidized will experience which of the following with respect to the electrons in its outer shell? (a) a net gain (b) a net loss (c) no change (d) an equal sharing

B

3-18 When elemental sodium is added to water, the sodium atoms ionize spontaneously. Uncharged Na becomes Na+. This means that the Na atoms have been _____________. (a) protonated. (b) oxidized. (c) hydrogenated. (d) reduced.

B

3-22 Seed oils are often dehydrogenated and added back into processed foods as partly unsaturated fatty acids. In comparison with the original oil, the new fatty acids have additional double carbon-carbon bonds, replacing what were once single bonds. This process could also be described as _____________. (a) isomerization. (b) oxidation. (c) reduction. (d) protonation.

B

3-26 Catalysts are molecules that lower the activation energy for a given reaction. Cells produce their own catalysts called _____________. (a) proteins. (b) enzymes. (c) cofactors. (d) complexes.

B

3-29 Enzymes facilitate reactions in living systems. Figure Q3-29 presents an energy diagram for the reaction XàY. The solid line in the energy diagram represents changes in energy as the reactant is converted to product under standard conditions. The dashed line shows changes observed when the same reaction takes place in the presence of a dedicated enzyme. Which equation below indicates how the presence of an enzyme affects the activation energy of the reaction (catalyzed versus uncatalyzed)? (a) d-cversusb-c (b) d-aversusb-a (c) a + d versus a + b (d) d-c versus b-a

B

3-3 The second law of thermodynamics states that the disorder in any system is always increasing. In simple terms, you can think about dropping NaCl crystals into a glass of water. The solvation and diffusion of ions is favored because there is an increase in _____________. (a) pH. (b) entropy. (c) ions. (d) stored energy.

B

3-35 Which of the following is true for a reaction at equilibrium? (a) ΔG=ΔG° (b) ΔG° + RT ln [X]/[Y] = 0 (c) RT ln [X]/[Y] = 0 (d) ΔG + ΔG° = RT ln [X]/[Y]

B

3-40 The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of _______________ in a process called _____________. (a) ATP, phosphorylation. (b) water, hydrolysis. (c) hydroxide, hydration. (d) acetate, acetylation.

B

3-48 Which of the following statements would not be true of a favorable binding equilibrium? (a) The free-energy change is negative for the system. (b) The concentration of the complex remains lower than the concentration of the unbound components. (c) The complex dissociation rate is slower than the rate for component association. (d) The binding energy for the association is large and negative.

B

3-2 When there is an excess of nutrients available in the human body, insulin is released to stimulate the synthesis of glycogen from glucose. This is a specific example of a(n) __________ process, a general process in which larger molecules are made from smaller molecules. (a) metabolic (b) catabolic (c) anabolic (d) biosynthetic

C

3-21 Oxidation and reduction states are relatively easy to determine for metal ions, because there is a measurable net charge. In the case of carbon compounds, oxidation and reduction depend on the nature of polar covalent bonds. Which of the following is the best way to describe these types of bond? (a) hydrogen bonds in a nonpolar solution (b) covalent bonds in an aqueous solution (c) unequal sharing of electrons across a covalent bond (d) equal sharing of electrons across a covalent bond

C

3-23 Chemical reactions that lead to a release of free energy are referred to as "energetically favorable." Another way to describe these reactions is: _____________. (a) uphill. (b) uncatalyzed. (c) spontaneous. (d) activated.

C

3-24 Even though cellular macromolecules contain a large number of carbon and hydrogen atoms, they are not all spontaneously converted into CO2 and H2O. This absence of spontaneous combustion is due to the fact that biological molecules are relatively __________ and an input of energy is required to reach lower energy states. (a) large (b) polar (c) stable (d) unstable

C

3-36 The equilibrium constant (K) for the reaction YàX can be expressed with respect to the concentrations of the reactant and product molecules. Which of the expressions below shows the correct relationship between K, [Y], and [X]? (a) K = [Y]/[X] (b) K = [Y] * [X] (c) K = [X]/[Y] (d) K = [X] - [Y]

C

3-41 When the polymer X-X-X... is broken down into monomers, it is "phosphorylyzed" rather than hydrolyzed, in the following repeated reaction: X-X-X... + PàX-P + X-X... (reaction 1) Given the ΔG° values of the reactions listed in the following table, what is the expected ratio of X-phosphate (X-P) to free phosphate (P) at equilibrium for reaction 1? (a) 1:106 (b) 1:104 (c) 1:1 (d) 104:1 X-X-X... + H2O -> X + X-X...DG° = - 4.5 kcal/mole X + ATP -> X-P + ADP DG° = -2.8 kcal/mole ATP + H2O -> ADP + P DG° = -7.3 kcal/mole

C

3-25 ΔG° indicates the change in the standard free energy as a reactant is converted to product. Given what you know about these values, which reaction below is the most favorable? (a) ADP + PiàATP ΔG° = +7.3 kcal/mole (b) glucose 1-phosphate à glucose 6-phosphate ΔG° = -1.7 kcal/mole (c) glucose + fructoseàsucrose ΔG° = +5.5 kcal/mole (d) glucoseàCO2 + H2O ΔG° = -686 kcal/mole

D

3-28 Figure Q3-28 is an energy diagram for the reaction XàY. Which equation below provides the correct calculation for the amount of free-energy change when X is converted to Y? (a) a+ b -c (b) a-b (c) a-c (d) c-a

D

3-31 A chemical reaction is defined as spontaneous if there is a net loss of free energy during the reaction process. However, spontaneous reactions do not always occur rapidly. Favorable biological reactions require ______________ to selectively speed up reactions and meet the demands of the cell. (a) heat (b) ATP (c) ions (d) enzymes

D

3-33 ΔG measures the change of free energy in a system as it converts reactant (Y) into product (X). When [Y] =[X], ΔG is equal to _____________. (a) ΔG°+RT (b) RT (c) ln [X]/[Y] (d) ΔG°

D

3-4 The energy used by the cell to generate specific biological molecules and highly ordered structures is stored in the form of _____________. (a) Brownian motion. (b) heat. (c) light waves. (d) chemical bonds.

D

3-42 In the case of a simple conversion reaction such as X->Y, which value of ΔG° is associated with a larger concentration of X than Y at equilibrium? (Hint: How is ΔG° related to K?) (a) ΔG°=-5 (b) ΔG°=-1 (c) ΔG° = 0 (d) ΔG° = 1

D

3-45 If proteins A and B have complementary surfaces, they may interact to form the dimeric complex AB. Which of the following is the correct way to calculate the equilibrium constant for the association between A and B? (a) kon/koff = K (b) K = [A][B]/[AB] (c) K = [AB]/[A][B] (d) (a) and (c)

D

3-55 The study of enzyme kinetics is usually performed with purified components and requires the characterization of several aspects of the reaction, including the rate of association with the substrate, the rate of catalysis, and _____________. (a) the enzyme's structure. (b) the optimal pH of the reaction. (c) the subcellular localization of the enzyme. (d) the regulation of the enzyme activity.

D