Chapter 8: Energy and Enzymes: An Introduction to Metabolism Flashcards
A reaction will be spontaneous at all temperatures under which set of conditions?
A) Both ΔH and ΔS are positive.
B) Both ΔH and ΔS are negative.
C) ΔH is positive, and ΔS is negative.
D) ΔH is negative, and ΔS is positive.
D) ΔH is negative, and ΔS is positive.
Considering the reaction CH4 (methane) plus O2 yields CO2 plus H2O plus energy, which of the following is true?
A) Oxygen gas acts as an electron donor.
B) The overall reaction is endergonic.
C) Methane acts as an electron donor.
D) Carbon dioxide has more potential energy than methane.
C) Methane acts as an electron donor.
If ATP hydrolysis took place in an acidic solution such that it no longer carried negative charges, how would you predict that the free energy released would change?
A) Less free energy will be released.
B) There will be no change in the free energy released.
C) There will be more free energy released.
D) Hydrolysis will not take place under acid conditions.
A) Less free energy will be released.
Compared with NAD+, NADH is ____.
A) oxidized and has less potential energy
B) oxidized and has less potential energy
C) reduced and has more potential energy
D) reduced and has less potential energy
C) reduced and has more potential energy
A chemical reaction that occurs spontaneously must ____.
A) proceed without an input of external energy
B) release heat energy
C) take place in a very short amount of time
D) produce products that are more disordered than the reactant molecules
A) proceed without an input of external energy
Which of the following factors affect the process of a chemical reaction?
A) substrate concentration
B) free energy changes
C) temperature
D) All the listed responses are correct.
D) All the listed responses are correct.
How do high temperatures speed chemical reactions?
A) Heat increases the concentration of reactants.
B) Heat makes reactions spontaneous.
C) Heat causes the reactants to move faster and collide more often.
D) High temperature decreases entropy, which increases the likelihood that reactants will collide.
C) Heat causes the reactants to move faster and collide more often.
When researchers analyzed the effects of temperature and reactant concentration on reaction rates (Figure 8.4), why were temperature and concentration examined separately?
A) High temperature and increased reactant concentration would cancel each other out, and no increase in reaction rate would be observed.
B) If higher temperatures and reactant concentrations were combined, researchers couldn’t tell which factor led to an increase in reaction rate.
C) It was experimentally impossible to vary both temperature and reactant concentration simultaneously.
D) The researchers wanted to be able to generate two graphs of data, not a single graph.
B) If higher temperatures and reactant concentrations were combined, researchers couldn’t tell which factor led to an increase in reaction rate.
The lowering of activation energy during the transition step of enzyme catalysis depends on _____ at the enzyme’s active site.
A) temperatures rising
B) products being released
C) interactions with R-groups
D) reactants orienting precisely
C) interactions with R-groups
Enzyme-catalyzed reactions increase in rate very rapidly at low substrate concentrations but plateau at higher substrate concentrations. Why?
A) As substrate concentrations increase, the concentrations of inhibitors increase to maintain homeostasis.
B) At high substrate concentrations, all available enzyme molecules are working at maximal speed and are unable to further increase the rate of reaction.
C) An activator is necessary to maintain high reaction rates when substrate concentrations are high.
D) Product concentrations are too high at high substrate concentrations.
B) At high substrate concentrations, all available enzyme molecules are working at maximal speed and are unable to further increase the rate of reaction.
Which one of the following processes would speed up a reaction rate by decreasing the activation energy?
A) increasing the amount of reactants
B) adding an inhibitor
C) adding a catalyst
D) adding heat
C) adding a catalyst
In graphs of enzyme activity versus temperature, activity increases up to a certain temperature and then decreases again. What is the mechanism that explains this pattern?
A) As temperatures increase, substrates collide with the enzyme more, but even higher temperatures cause too much enzyme movement and the enzyme denatures.
B) As temperatures increase, substrates collide with the enzyme more, but even higher temperatures slow substrate movement.
C) As temperatures increase, more cofactors will bind to enzymes, but even higher temperatures will decrease cellular cofactor concentrations to a level that decreases enzyme activity.
D) Enzymes have preferred temperature optima.
A) As temperatures increase, substrates collide with the enzyme more, but even higher temperatures cause too much enzyme movement and the enzyme denatures.
In what important way does competitive inhibition differ from allosteric inhibition?
A) During competitive inhibition, a regulatory molecule binds to a site other than the active site.
B) There is no difference as they are two different terms that mean the same thing.
C) During competitive inhibition, a regulatory molecule binds to the active site; during allosteric inhibition, a regulatory molecule binds to a site other than the active site.
D) Allosteric inhibition is important in maintaining homeostasis, whereas competitive inhibition is not.
C) During competitive inhibition, a regulatory molecule binds to the active site; during allosteric inhibition, a regulatory molecule binds to a site other than the active site.
Which one of the following factors is a covalent modification that can affect enzyme activity?
A) phosphorylation
B) pH
C) allosteric activation
D) competitive inhibition
A) phosphorylation
Which one of the following statements is true of enzyme phosphorylation?
A) Enzymes catalyze phosphorylation.
B) Phosphorylation does not use cellular energy.
C) Phosphorylation always inactivates enzymes.
D) Phosphorylation always activates enzymes.
A) Enzymes catalyze phosphorylation.
