Chapter 3 Bio 230

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) electrons, proton

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) enzymes

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 + Pi -> ATP ΔG° = +7.3 kcal/mole (b) glucose 1-phosphate -> glucose 6-phosphate ΔG° = -1.7 kcal/mole (c) glucose + fructose -->sucrose ΔG° = +5.5 kcal/mole (d) glucose --> CO2 + H2O ΔG° = -686 kcal/mole

(d) glucose-> CO2 +H2O

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

(d) kinetic

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) the rate of substrate consumption shortly after mixing the enzyme and substrate, for several substrate concentrations.

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) the regulation of the enzyme activity

True or False: CO2 gas is fixed in a series of reactions that are light-dependent

.False. The fixation of carbon from CO2 occurs independently of light.

A catalyst decreases the __________________ energy of a reaction.

A catalyst decreases the activation energy of a reaction.

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)

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)

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) CO2, H2O

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) CO2, Photosynthesis

For the reaction Y->X 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) DELTA G becomes less negative and DELTA G prime stays the same

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) slow

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) The concentration of the complex dissociation rate is slower than the rate for component association

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) a net loss

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) catabolic

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) enzymes

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) oxidation

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) oxidation.

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) oxidized

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) water, hydrolysis

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) binding energy

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

(c) entropy

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) heat

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) spontaneous

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) unequal sharing of electrons across a covalent bond

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)

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)

True or False: The second law of thermodynamics states that the total amount of energy in the Universe does not change.

False, The second law of thermodynamics states that components of any system move toward greater disorder. It is the first law of thermodynamics that states that energy is neither created nor destroyed.

True or False: Enzymes alter the equilibrium point of a reaction

False. An enzyme catalyzes its reaction in both directions. Enzymes do not affect the free energy of the reactants and products are the same, and thus they do not affect the reaction equilibrium.

True or False: Enzymes increase the average energy of reactant molecules.

False. By lowering the energy of activation, enzymes increase the number of molecules in a population that can overcome the activation barrier.

Competitive inhibitors bind irreversibly to the enzyme active site, lowering Vmax.

False. Competitive inhibitors bind reversibly to an enzyme's active site.

True or False: Enzymes lower the free energy released by the reaction that they facilitate.

False. Enzymes do no affect the intial energy of the reactants nor the final energy of the products after the reaction is complete, which are the values that determine the change in free energy of a reaction.

True or False: When two macromolecules form a complex, the free energy of the system increases because there is a net increase in the amount of order in the cell.

False. Even nonspecific interactions between macromolecules can be favorable if there is a large number of water molecules and ions displaced at the interaction interface. This would lead to an overall increase in disorder, even though the two larger molecules become associated and more ordered.

Vmax can be determined by measuring the amount of product accumulated later in the reaction.

False. Initial reaction velocities are measured to determine Vmax.

True or false: photosynthetic organisms release only O2 into the atmosphere, while nonphotosynthetic organism release only CO2.

False. Plants, as well as photosynthetic algae and bacteria, perform photosynthesis and respiration. This means that photosynthetic organisms release both O2 and CO2 into the atmosphere.

True or False: The diffusion rated for smaller molecules in the cytosol are much lower than what is observed for the same molecules in water.

False. Small molecules diffuse through the cytosol nearly as rapidly as they diffuse in water.

True or False: H2 is the most stable and abundant form of hydrogen in the environment.

False. The most stable form of hydrogen is H2O

True or False: The ultimate source of energy for living systems is chlorophyll.

False. The ultimate source of energy for living organisms is sunlight.

If you weigh yourself on a scale one morning, then eat four pounds of food during the day, will you weigh four pounds more the next morning? Why or why not? (Hint: What happens to the atoms from the food you ingested?)

NO, you will not weigh four pounds more the next morning because only a small portion of the mass of the food will form components of the body. Much of the mass of food is either released as CO2 and H2O that are breathed out into the atmosphere or converted into materials excreted as waste products.

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)

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)

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) Stable

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)

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) CHEMICAL BONDS

The equilibrium constant (K) for the reaction Y->X 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) K = X/Y

Which of the values listed below is used to calculate the enzyme turnover number? (a) ½Vmax (b) Km (c) Vmax (d) Vmax - Km

(c) Vmax

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) anabolic

By definition, catalysis allows a reaction to occur more __________________.

By definition, catalysis allows a reaction to occur more rapidly.

Although the biochemical study of reaction rates and free energies is important for understanding each biological reaction individually, these studies do not provide an accurate picture of what is happening to reactants and products inside the cell. Why not?

Chemical reactions inside the cell do not reach a state of equilibrium because both reactants and products are typically used in more than one set of reactions, which means their concentrations are constantly fluctuating. As a result, the forward and reverse reaction are almost never identical.

Chemical reactions occur only when there is a loss of __________________ energy

Chemical reactions occur only when there is a loss of free energy.

Enzymes act more __________________ than other catalysts

Enzymes act more selectively than other catalysts.

True or False: During cellular respiration, carbon-containing molecules become successively more oxidized until they reach their most oxidized form, as CO2.

True

True or False: Enzymes increase the probability that any given reactant molecule will be converted to product.

True

True or False: Enzymes lower the activation energy for a specific reaction.

True

True or False: Sequential pathways can help drive unfavorable reactions by siphoning off the products into the next energetically favorable reaction in the series.

True

True or False: The cycling of carbon through the biosphere first requires the incorporation of inorganic CO2 into organic molecules.

True

True or False: The cytosol is densely packed with molecules, creating what is more an aqueous gel than a solution.

True

True or False: The oxidation of one molecule is always coupled to the reduction of a second molecule.

True