BIO Chapter 8 Review Questions
If a reaction is exergonic, then which of these statements is true? A. The products have lower Gibbs free energy than the reactants. B. Energy must be added for the reaction to proceed. C. The products have lower entropy (are more ordered) than the reactants. D. The reaction always occurs quickly.
A
You have discovered an enzyme that appears to function only when a particular sugar accumulates. Which of the following scenarios would you predict to be responsible for activating this enzyme? A. the sugar cleaves the enzyme to form the active conformation. B. the sugar is an allosteric regulatory molecule for the enzyme. C. the sugar is a competitive inhibitor for the enzyme D. the sugar phosphorylates the enzyme to form the active conformation
B- the sugar likely binds to the enzyme and changes its structure to form a functional active site
What is a transition state? A. the shape adopted by an enzyme that has an inhibitory molecule bound at its active site. B. the amount of kinetic energy required for a reaction to proceed. C. the intermediate complex formed as covalent bonds in the reactants are being broken and re-formed during a reaction. D. the structure of an enzyme when an allosteric regulatory molecule binds to it
C
Draw a chemical equation to represent the redox reaction that occurs when methane (CH4) burns in the presence of oxygen (O2). Identify the reactant that is being reduced and the reactant that is being oxidized. Of the four molecules that should be in your equation, point out the one that has the highest energy bonds.
CH4 + 2 O2 --> CO2 + 2 H2O CH4 will be reduced. O2 will be oxidized. CH4 has highest energy bonds.
How does pH affect an enzyme-catalyzed reactions? A. Protons serve as a substrate for most reactions. B. Energy stored in protons is used to drive endergonic reactions. C. Proton concentration increases the kinetic energy of the reactants, enabling them to reach their transition state. D. The concentration of protons affects an enzyme's folded structure and reactivity.
D
If you were to expose glucose to oxygen on your lab bench, why would you not expect to see it burn as shown in Figure 8.6? A. the reaction is endergonic and requires an input of energy. B. the reaction is not spontaneous unless an enzyme is added to the substrates. C. the sugar must first be phosphorylated to increase its potential energy. D. activation energy is required for the sugar and oxygen to reach their transition state.
D- energy, such as thermal energy in fire, must be provided to overcome the activation energy barrier before the reaction can proceed.
Explain the lock and key model of enzyme activity. What is incorrect about this model?
Reactions proceed when the reactant molecules (the key) fits snugly into the active site of an enzyme (the lock). Fischer's original model assumed that enzymes were rigid; in fact, enzymes are flexible and often change their shape after binding to substrates.
Explain how feedback inhibition regulates metabolic pathways.
The final product of a pathway inhibits the activity of an enzyme early in the same pathway, thus reducing the activity of all subsequent steps in the pathway.
