Biochemistry Practice Problems VI with Answers

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1. Proteases typically _________for their enzymatic action, and break the __________ bond at _____________ .
a. are non-specific / carbonyl / multiple locations in proteins
b. require a zinc cofactor / amino-carbon / locations near hydrolysis sites
c. require vitamin C / cross-linking / intrastrand alpha helix locations
d. show specificity / peptide / locations adjacent to certain amino acid side chains

2. HIV-1 protease functions to:
a. activate aspartate residues of the two subunits
b. translate the gag-pol gene to a polyprotein
c. cleave a zymogen to produce an active product
d. replicate the viral DNA imported into the infected cell

3. The regulatory influence of one subunit of Protein Kinase A on the other type of PKA
subunit is essentially the same as ______________.
a. competitive inhibition
b. noncompetitive inhibition
c. positive allosterism
d. covalent modification

4. The slowest step of a multi-step enzyme pathway is termed the:
a. major regulated step
b. feedback control step
c. rate-limiting step
d. kinetic control step

5. Which of the following is true regarding allosteric modulators of enzyme activity?
a. typically do not alter Vmax
b. in most cases, do not alter Km
c. generally speaking, are irreversible in nature
d. all of the above are true

6. Proteolytic activation is a regulatory process that is ____________ and which modifies a(n) _______________ to form an active, functional product.
a. negative allosteric / enzyme active site
b. reversible / regulatory protein
c. irreversible / zymogen
d. noncompetitive / acetylhistone
7. Which of the following is a correct statement regarding substrate binding of the Cytochrome P450 enzyme system?
a. Isotypes generally bind only one substrate within the active site
b. Coumarin metabolism demonstrates that specific reactions occur
c. Induction may be allosterically modulated by substrate binding
d. Termed “promiscuous” due to the large variety of genetic isoforms that exist

8. In the CYP450 reaction cycle, the first electron reduces _________ , while the second electron is used to reduce ____________ .
a. oxygen / ferrous iron
b. ferrous iron / hypervalent oxygen
c. ferric iron / oxygen
d. P450 reductase / ferric iron: O2 complex

9. The phenomena of induction is best described as:
a. chemical-induced alteration of gene expression of a specific isotype
b. falling level of DNA due to lack of gene expression produced by substrate inhibition
c. alteration of effector molecule activity to express more of an abnormal isotype
d. racial, geographic or other factors that are predictive or cautionary for drug use

10. The heme molecule found in CYP450 functions to:
a. bind the reactive species of iron during its activation in order to facilitate the delivery
of an electron to a substrate
b. hold the partner protein in place so that transfer of electrons is facilitated in a timely
manner and uncoupling is prevented
c. bind an oxygen molecule near to the substrate so that an atom of oxygen can be transferred to the substrate
d. hold the enzyme:substrate complex in position so that the oxygen molecule can be
transferred from the P450 reductase complex

11. If a specific isotype of P450 responsible for metabolism of active parent drug X has been inhibited, then drug X would be expected to:
a. cause inhibition of the specific P450 isotype at nuclear receptors
b. disappear more rapidly from plasma and exert less clinical actions
c. drug levels are not changed; affinity is modified but Vmax can be reached
d. produce greater clinical effects due to its elevated plasma concentration

12. Which of the following statements correctly characterizes P450 substrates that are
metabolized in the mitochondria?
a. Generally are lipophilic drugs
b. Usually are endogenous substances
c. Typically are processed by Phase II pathways
d. In most cases are environmental toxins