Biochem Finals Chapter 11

Front 1

All of the following are correct about a cytochrome P450 molecule except:
a. It contains a heme as a prosthetic group
b. It catalyzes the hydroxylation of a hydrophobic substrate
c. it may accept electrons from a substance such as NADPH
d. it undergoes a change in the heme iron upon binding a substrate
e. it comes from the same gene family as all other cytochrome P450

Back 1

e. it comes from the same gene family as all other cytochrome P450
Several gene families are known

Front 2

Flavoproteins are usually intermediates in the transfer of electrons from NADPH to cytochrome P450 because:
a. NADPH cannot enter the membrane
b. Flavoproteins can accept two electrons from NADPH and donate them one at a time to cytochrome P450
c. They have a more negative reduction potential than NADPH so accept electrons more readily
d. As proteins, they can bind to cytochrome P450 while the nonprotein NADPH cannot
e. They contain iron-sulfur centers

Back 2

b. Flavoproteins can accept two electrons from NADPH and donate them one at a time to cytochrome P450

Front 3

In the conversion of cholesterol to steroid hormones in the adrenal gland
a. all of the cytochrome P450 oxidations occur in the endoplasmic reticulum
b. all of the cytochrome P450 oxidations occur in the mitochondria
c. side-chain cleavage of cholesterol to pregnenolone is one of the cytochrome P450 systems that uses adrenodoxin reductase
d. cytochrome P450 is necessary for the formation of aldosterone and cortisol but not for the formation of androgens and estrogens

Back 3

c. side-chain cleavage of cholesterol to pregnenolone is one of the cytochrome P450 systems that uses adrenodoxin reductase

Front 4

Genetic polymorphism in genes for cytochrome P450:
a. Could cause an individual to metabolize poorly certain drugs
b. Could cause an individual to metabolize certain drugs more rapidly than normal
c. Could cause a specific ethnic group to experience more effects with certain drugs
d. All of the above

Back 4

d. All of the above

Front 5

In the presence of active NOS but absence of substrate
a. electrons cannot be transferred to heme
b. calmodulin cannot bind Ca2+
c. the oxygenase and reductase domains dissociate
d. cGMP production is increased
e. superoxide and/or hydrogen peroxide will be formed

Back 5

e. superoxide and/or hydrogen peroxide will be formed
These are toxic to the body

Front 6

Nitric oxide:
a. is formed spontaneously by a reduction of NO2
b. is synthesized only in macrophages
c. is synthesized from arginine
d. acts as a potent vasoconstrictor
e. has three isoforms

Back 6

c. is synthesized from arginine
(NO Synthase has three isoforms)

Front 7

Nitric oxide synthase:
a. catalyzes a dihydrogenase reaction
b. is similar to cytochromes P450 in binding zinc and tetrahydrobiopterin
c. accepts electrons from NADH
d. uses a flow of electrons from NADPH to FAD to FMN to heme-iron
e. is inhibited by Ca2+

Back 7

d. uses a flow of electrons from NADPH to FAD to FMN to heme-iron

Front 8

NADPH-cytochrome P450 reductase:
a. uses both FAD and FMN as prosthetic groups
b. binds to cytochrome P450 by strong hydrophobic interactions
c. requires an iron-sulfur center for activity
d. can use NADH as readily as NADPH

Back 8

a. uses both FAD and FMN as prosthetic groups

Front 9

Which of the following treatments would increase the likelihood of toxicity resulting from acetaminophen overdose?
A) Taking a drug which increases cytochrome p450 activity
B) Taking a an agent which increases glutathione intracellular levels
C) Taking a compound which increases the fluidity of the plasma membrane
D) Taking a compound which inhibits inducible NOS (2) activity
E) Taking a compound that increases renal elimination of sulfate conjugates

Back 9

A) Taking a drug which increases cytochrome p450 activity

Front 10

What is the source (transfer to heme) of the single electron that is responsible for oxidation in NOS enzyme family?
A) Zn++
B) NADPH
C) NAD+
D) FMN
E) FAD

Back 10

D)FMN

Front 11

Which of the following statements is true for the protein calmodulin?
A) Increase electron transfer for cytochrome p450
B) Is a zinc dependent enzyme
C) Is coupled to sphingolipid transport
D) Is important for eNOS activity
E) Is associated with the lateral movement of phospholipids

Back 11

D) Is important for eNOS activity

Front 12

Which of the following statements is true for ER associated cytochrome P450
A) Is responsible for the synthesis of sphingolipids
B) Utilizes the iron in the oxidized form (ferrous) for interaction with BH4
C) Utilizes andrioreductase for optimal activity
D) It is associated with the membrane through a GPI linkage
E) Generates water as a product in oxidation reactions

Back 12

E) Generates water as a product in oxidation reactions

Front 13

Which of the following vitamins is important in the assisting in the proper activating of NOS but not cytochrome p450
A) Folic Acid
B) Niacin
C) Riboflavin
D) Pyridoxine
E) Ascorbic Acid

Back 13

A) Folic Acid

Front 14

The enzyme NADPH-adrenodoxin reductase is associated with which of the following systems
A) Mitochondrial cytochrome P450
B) ER cytochrome p450
C) Neuronal NOS
D) Acetylcholine esterase
E) Inducible NOS (NOS 2)

Back 14

A) Mitochondrial cytochrome P450

Front 15

Drugs can be considered xenobiotics (exogenous substances metabolized by the body). Many xenobiotics are oxidized by cytochromes P450 in order to
A) make them carcinogenic
B) increase their aqueous solubility
C) increase their partition coefficient and deposition in adipose tissue
D) increase their pharmacological activity
E) all of the above

Back 15

B) increase their aqueous solubility

Front 16

Which of the following statements is FALSE in relationship to steroid hormone production during pregnancy?
A) Cytochromes P450 play a major role in estrogen synthesis
B) All of estrogen is produced by Fetal Cytochrome P450 during pregnancy
C) The corpus lutem of the ovary is the major site for estrogen production in the first few weeks of pregnancy.
D) The human placenta lacks CYP17 which catalyzes both 17 alpha hydroxylation reaction and cleavage of C17-C20 bond.
E) The fetal adrenal gland catalyzes the synthesis of DHEA from cholesterol

Back 16

B) All of estrogen is produced by Fetal Cytochrome P450 during pregnancy

Front 17

True/False
NADH and NADPH can transfer electrons sequentially rather than all at once.

Back 17

False

Front 18

True/False
Flavin adenine dinucleotide can transfer electrons sequentially rather than all at once.

Back 18

True

Front 19

Which of the coenzymes can undergo sequential and which can undergo simultaneous oxidation by double electron transfer?

Back 19

FMN can undergo sequential oxidation/reduction
NAD can only undergo simultaneous oxidation/reduction

Front 20

True/False
Cofactors are inorganic ions that bind to an enzyme stabilize the electron configuration of the substrate thus facilitating catalysis.

Back 20

True

Front 21

True/False
The fetal adrenal gland in pregnancy is catalyzes the synthesis of 16 alpha-hydroxy-dehydroepiandrosterone (16-alphahydroxy-DHEA) that is converted to estrogen by the CYP19 in the placenta.

Back 21

True

Front 22

True/False
Flavin adenine dinucleotide can transfer electrons sequentially rather than all at once.

Back 22

True

Front 23

Cytochrome P450 CYP2E1 is involved in acetaminophen metabolism. Which of the following statements is NOT true:
a.) is expressed in very low amounts in the liver
b.) will metabolize acetaminophen into a toxic metabolite that upon reacting with glutathione is eliminated from the body.
c.) CYP2E1 levels can be induced by ethanol
d.) Depletion of glutathione results in the reaction of the acetaminophen toxic metabolite with cellular proteins resulting in cell death.
e.) Ethanol is a substrate for CYP2E1
f.) All of the statements are true.

Back 23

f.) All of the statements are true.