Molec and Cell Chapter 3

Assume that the average human adult requires 2000 kilocalories per day to sustain all normal processes and maintain a constant weight. If manufactured solar panels could somehow provide power directly to the human body, what size solar panel would be required (in cm2)? Assume there are 10 hours of sunlight per day, and that the usable energy output for a typical solar panel is 850 kJ/ft2 per hour. Note: 1 kcal = 4.184 kJ 1 ft2 = 929.03 cm2

1 kcal = 4.184 kJ 1 ft2 = 929.03 cm2 If there are 10 hours of sunlight each day hitting the solar panel, there are 8500 kJ/ft2 produced per day. The average adult human requires 8368 kJ per day; thus, with a conventional solar panel, we would require a surface area of about a square foot, or more precisely in cm2: 8368 kJ/X = 8500 kJ/929.03 cm2 929.03 µltiply 8368/8500 = X X=914.57 cm^2

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?

1/Vmax and 1/Km

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?

16.98

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... + P ! X-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?

1:1

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.

80 seconds

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 net loss

During respiration, energy is retrieved from the high-energy bonds found in certain organic molecules. What are the ultimate products of respiration?

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. One carbon has been oxidized to _______________________, its most stable form, it can only cycle back into the organic portion of the carbon cycle through _____________________.

CO2, photosynthesis

Organize the following molecules in order with respect to their relative levels of oxidation; CH2O (formaldehyde) ; CH4 (methane); CHOOH (formic acid) ; CH3OH (methanol); CO2 (carbon dioxide)

CO2; CHOOH; CH2O; CH3OH; CH4

True or False; Enzymes alter the equilibrium point of a reaction.

False (An enzyme catalyzes its reaction in both directions, lowering the energy of activation for both the forward and reverse reactions. 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)

True or False; 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; 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)

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; 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; CO2 gas is fixed in a series of reactions that are light-dependent

False(The fixation of carbon from CO2 occurs independently of light)

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

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

Chemical reactions that lead to a release of free energy are referred to as "energetically favorable." Another way to describe these reactions is : ________________________.

Spontaneous

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.

The binding energy of the ES interaction is greater than that of the EI interaction.

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.

The concentration of the complex remains lower than the concentration of the unbound components

A catalyst decreases the _________________________ energy of a reaction.

activation

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 specif example of a ____________________ process, a general process in which larger molecules are made from smaller molecules

anabolic

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)

a and c

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 ____________________.

binding energy

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 _____________________.

catabolic

The energy used by the cell to generate specific biological molecules and highly ordered structures is stored in the form of _________________________.

chemical bonds

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.

condensation

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?

creatine phosphate and enzyme A

The anhydride formed between a carboxylic acid and a phosphate (Figure Q369A) 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?

It decreases the stability of the high-energy intermediate

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]

K = [X]/[Y]

Light + _________________ + _________________ = _____________________ + heat + sugars

Light + H2O + CO2 = O2 + heat + sugars

In the first stage of photosynthesis, light energy is converted into what other form of energy?

electrical or kinetic

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

electrons, proton

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 _________________.

entropy

A chemical reaction id defined as spentaneous 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.

enzymes

Catalysts are molecules that lower the activation energy for a given reaction. Cells produce their own catalysts called ____________________.

enzymes

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

free

Delta G 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

glucose = CO2 + H2O ΔG° = -686 kcal/mole

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 __________________.

heat

Seeds oils are often dehydrogenated and added back into processed foods as partly unsaturated fatty acids have additional double carbon-carbon bonds, replacing what were once single bonds. This process could also be described as ___________________.

oxidation

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?

oxidation

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. Figure Q3-71 Which molecule is added to glutamic acid in the activation step?

phosphate

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. Figure Q3-72 In the condensation step, _______________ is displaced by ________________.

phosphate, NH3

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

rapidly

Enzymes act more __________________________ than other catalysts.

selectively

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 fore the dispersion of small molecules over short distances

slow

Even though cellular macromolecules contain a large number of carbon and hydrogen atoms, they are nota ll spontaneously converted into CO2 and H2O. This absence of spontaneous combustion is due to the fact that biological molecules are relatively _________________ and input of energy is required to reach lower energy states.

stable

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?

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

The potential energy stored in high-energy bonds is commonly harnessed when the bonds are split by the addition of ______________________ in a process called _____________________.

water, hydrolysis

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?

ΔG becomes less negative and ΔG° stays the same.

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 _____________.

ΔG°

Which 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]

ΔG° + RT ln [X]/[Y] = 0

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?)

ΔG° = 1

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 molecules below is the most widely used activated carrier?

ATP

True or False; The diffusion rates 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; Photosynthetic organisms release only O2 into the atmosphere, while nonphotosynthetic organisms release only CO2.

False (

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

False ( Enzymes do not affect the initial 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; Vmax can be determined by measuring the amount of product accumulated late in the reaction

False ( Initial reaction velocities are measured to determine Vmax.)

When elemental sodium is added to water, the sodium atoms ionize spontaneously. Uncharged Na becomes Na+. This means that the Na atoms have been ______________________.

Oxidized

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 _________________________.

The regulation of the enzyme activity

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

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. What is the best way to describe these types of bond?

Unequal sharing of electrons across a covalent bond

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?

Vmax