For each question, choose the ONE BEST answer or completion.
1. Conformational or shape changes in proteins allow
A. conversion of chemical energy into kinetic (movement) energy.
B. cooperativity between subunits in a quaternary structure.
C. allosteric control of enzymes.
D. proteins to carry other molecules across membranes.
E. all of the above.
2. The turnover or catalytic constant (kcat) of an enzyme is
A. the number of molecules of substrate converted to product per mole of enzyme per unit time.
B. the time taken for a single catalytic event.
C. the number of substrate molecules in a mole.
D. the number of moles of substrate converted to product per mole of enzyme per unit time.
E. the initial velocity of the reaction when half the enzyme molecules have bound substrate.
3. The oxygen-binding curve for hemoglobin is S-shaped: starting from zero oxygen, the first small increase in oxygen concentration produces hardly any binding to hemoglobin. The next increase in oxygen produces much more binding so that the curve gets steeper before leveling off again as the hemoglobin becomes fully loaded. Hemoglobin can show this behavior because
A. it contains heme prosthetic groups.
B. it contains magnesium, in contrast to the iron in myoglobin.
C. it comprises two a chains of high oxygen affinity and two f chains of low oxygen affinity.
D. its four subunits can exist in one of two states, only one of which has a high affinity for oxygen. The way that the four subunits fit together means that they all must be in one form or the other. When oxygen concentration is low, most of the hemoglobin molecules have their subunits in the low-affinity form. As oxygen binds, more molecules switch to the high-affinity form.
E. its four subunits can exist in one of two states, only one of which has a high affinity for oxygen. The way that the four subunits fit together means that they all must be in one form or the other. When oxygen concentration is low, most of the hemoglobin molecules have their subunits in the high-affinity form. As oxygen binds, more molecules switch to the low-affinity form.
4. Which of the following statements about enzymes is false?
A. They bind their substrate.
B. They lower the activation energy for the reaction they catalyze.
C. They alter the equilibrium constant for the reaction they catalyze.
D. They stabilize intermediates along the pathway of the reaction they catalyze.
E. They can change shape to promote the reaction.
5. Protein kinases alter the conformation of their target protein by adding
B. phosphate groups.
C. histidine residues.
E. heme groups.
6. A prosthetic group is
A. a highly charged domain or motif that alters the shape of a protein.
B. a nonprotein molecule that is loosely attached to a protein and helps it to perform its function.
C. a nonprotein molecule that is tightly bound to a protein and helps it to perform its function.
D. a steroid molecule attached to a histidine residue.
E. a region of a protein that can accept a phosphate group.
A. produces a product that is inevitably broken down to pyruvate.
B. uses ATP as a substrate in its catalytic site.
C. binds ATP at a regulatory site.
D. works more slowly if ATP concentrations increase.
E. all of the above.
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