Clinical Biochem Test 4

Front 1

All of the following statements about acetyl-CoA carboxylase are correct except:
a. catalyzes rate limiting step of fatty acid synthesis
b. it requires biotin
c. it is inhibited by cAMP mediated phosphorylation
d. it is activated by palmitoyl CoA
e. its content in a cell responds to changes in fat content in diet.

Back 1

D. activated by citrate and inhibit by long chain fatty acyl CoAs

Front 2

During synthesis of palmitate in liver cells:
A. addition of malonyl-CoA to fatty acid synthase elongates the growing chain by 3 carbon units
B. a beta-keto acyl residue on 4-phosphopantetheine moeity is reduced to saturated residue by NADH
C. palmitoyl CoA is released from the synthase
D. transfer of growing chain from ACP to anther -SH occurs after addition of next malonyl-CoA
E. first compound to add fatty acid synthase is malonyl-CoA

Back 2

B. a beta-keto acyl residue on 4-phosphopantetheine moeity is reduced to saturated residue by NADH

Front 3

In humans, desaturation of fatty acids:
A. occurs primarily in mitochondria
B. is catalyzed by enzyme system that uses NADPH and a cytochrome
C. introduces double bonds primarily of trans configuration
D. can occur only after palmitate has been elongated to stearic acid
E. introduces the first double bond at the methyl end of the molecule

Back 3

B. is catalyzed by enzyme system that uses NADPH and a cytochrome

Front 4

All of the following events are usually involved in the synthesis of TAGs except:
A. addition of fatty acyl CoA to diacylglycerol
B. addition of fatty acyl CoA to lysophosphatide
C. reaction catalyzed by glycerol kinase
D. hydrolysis of phosphatidic acid by a phosphatase
E. reduction of dihydroxyacetone phosphate

Back 4

C. reaction catalyzed by glycerol kinase

Front 5

Lipoprotein Lipase:
A. is an intracellular enzyme
B. is stimualted by cAMP-mediated phosphorylation
C. functions to mobilize stored triacylglycerols from adipose tissue
D. is stimulatd by one of the apoproteins present in VLDL
E. produces free fatty acids and a monoacylglycerol

Back 5

D. is stimulatd by one of the apoproteins present in VLDL

Front 6

The high glucagon/insulin ratio seen in starvation:
A. promotes mobilization of fatty acids from adipose stores
B. stimulates Beta-oxidation by inhibiting the production of malonyl-CoA
C. leads to increased concentrations of ketone bodies in the blood
D. all the above
E. none of the above

Back 6

D. all the above

Front 7

A deficiency of carnitine might be expected to interfere with:
A. beta-oxidation
B. ketone body formation from Acetyl-CoA
C. palmitate synthesis
D. mobilization of stored triacylglycerols from adipose tissue
E. uptake of fatty acids into cells from the blood

Back 7

A. beta-oxidation

Front 8

A child is diagnosed with carnitine-acylcarnitine translocase deficiency. Diet low in long-chain fatty acids supplemented with medium chain TAG is beneficial because
A. child can get all required energy from carbohydrates
B. deficiency was in peroxisomal system so carnitine would not be helpful
C. medium chain fatty acids (8-10) enter the mitochondria before being converted to their CoA derivatives
D. medium chain TAGs contain mostly hydroxylated fatty acids
E. medium chain fatty acids such as C8 and C10 are readily converted into glucose by the liver

Back 8

C. medium chain fatty acids (8-10) enter the mitochondria before being converted to their CoA derivatives

Front 9

Beta-oxidation of fatty acids:
A. generates ATP only if acetyl-CoA is subsequently oxidized
B. is usually suppressed during starvation
C. uses only even-chain saturated fatty acids as substrates
D. uses NADP+
E. occurs by a repeated sequence of four reactions.

Back 9

E. occurs by a repeated sequence of four reactions.

Front 10

10) The lack of ketone in the presence of low blood glucose in this case is unusual since ketone body concentrations usually increase with fasting-induced hypoglycemia. Ketone bodies:
A. Are formed by removal of CoA from the corresponding intermediate of β-oxidation.
B. Are synthesized from cytoplasmic β-hydroxy-β-methyl glutaryl coenzyme A (HMG-CoA).
C. Are synthesized primarily in muscle tissue.
D. Include both β-hydroxybutyrate and acetoacetate, the ratio reflecting the intramitochondrial [NADH]/ [NAD+] ratio in the liver.
E. Form when β-oxidation is interrupted.

Back 10

D. Include both β-hydroxybutyrate and acetoacetate, the ratio reflecting the intramitochondrial [NADH]/ [NAD+] ratio in the liver.

Front 11

α-Oxidation:
A. Is important in the metabolism of branched-chain fatty acids.
B. Metabolizes a fatty acid completely to acetyl CoA.
C. Produces hydrogen peroxide.
D. Prevents the fatty acid from producing energy.
E. Requires NADPH.

Back 11

A. Is important in the metabolism of branched-chain fatty acids.

Front 12

Another minor pathway of fatty acid oxidation, ω-oxidation, also results in a hydroxylation. ω-Oxidation:
A. Occurs in mitochondria.
B. Introduces the –OH on the carbon adjacent to the carboxyl group.
C. Oxidizes primarily very-long-chain fatty acids.
D. Oxidizes the terminal methyl group.
E. Produces dicarboxylic acids in the initial oxidation.

Back 12

D. Oxidizes the terminal methyl group.

Front 13

Roles of various phospholipids include all of the following except:
A. Cell-cell recognition.
B. A surfactant function in lung.
C. Activation of certain membrane enzymes.
D. Signal transduction.
E. Mediator of hypersensitivity and acute inflammatory reactions.

Back 13

A. Cell-cell recognition.

Front 14

CDP-X (where X is the appropriate alcohol) reacts with 1,2-diacylglycerol in the primary synthetic pathway for:
A. Phosphatidylcholine.
B. Phosphatidylinositol.
C. Phosphatidylserine.
D. All of the above.
E. None of the above.

Back 14

A. Phosphatidylcholine.

Front 15

Phospholipases A1 and A2:
a. Have no role in phospholipid synthesis.
b. Are responsible for initial insertion of fatty acids in sn-1 and sn-2 positions during synthesis.
c. Are responsible for base exchange in the interconversion of phosphatidylethanolamine and phosphatidylserine.
d. Hydrolyze phosphatidic acid to a acylglycerol.
e. Remove a fatty acid in an sn-1 or sn-2 position so it can be replaced by another in phospholipid synthesis.

Back 15

E. Remove a fatty acid in an sn-1 or sn-2 position so it can be replaced by another in phospholipid synthesis.

Front 16

Bile acids differ from their precursor cholesterol in that they:
a. Are not amphipathic.
b. Contain an ionizable carboxyl group.
c. Contain less oxygen.
d. Are synthesized primarily in the intestine.
e. Contain more double bonds.

Back 16

B. Contain an ionizable carboxyl group. (conjutated to taurine or glycine)

Front 17

A ganglioside may contain all of the following except:
a. A ceramide structure.
b. Glucose or galactose.
c. Phosphate.
d. One or more sialic acids.
e. Sphingosine.

Back 17

C. Phosphate.

Front 18

Phosphatidlyinositols:
a. Are neutral phospholipids.
b. Are found primarily in mitochondrial membrane.
c. Release Ca2+ from the endoplasmic reticulum.
d. Can serve to anchor glycoproteins to cell surfaces.
e. Are the major surfactants maintaining normal lung function.

Back 18

D. Can serve to anchor glycoproteins to cell surfaces.

Front 19

Prostaglandin synthase, a bifunctional enzyme:
a. Catalyzes rate-limiting step of prostaglandin synthesis.
b. Is inhibited by anti-inflammatory steroids.
c. Contains both a cyclooxygenase and a peroxidase component.
d. Produces PGG2 as the end product.
e. Uses as substrate the pool of free arachidonic acid in the cell.

Back 19

C. Contains both a cyclooxygenase and a peroxidase component.

Front 20

Hydroperoxyeicosatetraenoic acids (HPETEs):
a. Are derived from arachidonic acid by peroxidase reaction.
b. Are mediators of hypersensitivity reactions.
c. Are intermediates in formation of leukotrienes.
d. Are relatively stable compounds (persist for as long as 4 hours).
e. Are inactivated forms of leukotrienes.

Back 20

C. Are intermediates in formation of leukotrienes.

Front 21

In biosynthesis of cholesterol:
a. 3-hydroxy-3-methyl glutaryl CoA (HMG CoA) is synthesized by mitochondrial HMG CoA synthase.
b. HMG-CoA reductase catalyzes the rate-limiting step.
c. The conversion of mevalonic acid to farnesyl pyrophosphate proceeds via condensation of 3 molecules of mevalonic acid.
d. Condensation of 2 farnesyl pyrophosphates to form squalene is freely reversible.
e. Conversion of squalene to lanosterol is initiated by formation of the fused ring system, followed by addition of oxygen.

Back 21

B. HMG-CoA reductase catalyzes the rate-limiting step.

Front 22

Cholesterol present in LDL (low-density lipoproteins):
a. Binds to a cell receptor and diffuses across the cell membrane.
b. When it enters a cell, suppresses activity of ACAT (acyl-CoA-cholesterol acyl transferase).
c. Once in the cell is converted to cholesteryl esters by LCAT (lecithin-cholesterol acyl transferase).
d. Once it has accumulated in the cell, inhibits replenishment of LDL receptors.
e. Represents primarily cholesterol that is being removed from peripheral cells.

Back 22

D. Once it has accumulated in the cell, inhibits replenishment of LDL receptors.

Front 23

All of the following are true about degradation of sphingolipids except it:
a. Occurs by hydrolytic enzymes contained in lysosomes.
b. Terminates at level of ceramides.
c. Is a sequential, stepwise removal of constituents.
d. May involve a sulfatase or a neuraminidase.
e. Is catalyzed by enzymes specific for a type of linkage rather than specific compound.

Back 23

B. Terminates at level of ceramides.

Front 24

In Niemann-Pick disease, the deficient enzyme is sphingomyelinase. Sphingomyelins differ from other sphingolipids in that they are:
a. Not based on a ceramide core.
b. Acidic rather than neutral at physiological pH.
c. Only types containing N-acetylneuraminic acid.
d. Only types that are phospholipids.
e. Not amphipathic.

Back 24

D. Only types that are phospholipids.

Front 25

Aminotransferases:
a. Usually require α-ketoglutarate or glutamine as one of the reacting pair.
b. Catalyze reactions that result in a net use or production of amino acids.
c. Catalyze irreversible reactions.
d. Require pyridoxal phosphate as an essential cofactor for the reaction.
e. Are not able to catalyze transamination reactions with essential amino acids.

Back 25

d. Require pyridoxal phosphate as an essential cofactor for the reaction.

Front 26

The production of ammonia in the reaction catalyzed by glutamate dehydrogenase:
a. Requires the participation of NADH or NADPH.
b. Proceeds though a Schiff base intermediate.
c. May be reversed to consume ammonia if it is present in excess.
d. Is favored by high levels of ATP or GTP.
e. Would be inhibited when gluconeogenesis is active.

Back 26

c. May be reversed to consume ammonia if it is present in excess.

Front 27

All of the following are correct about ornithine except it:
a. May be formed from or converted to glutamic semialdehyde.
b. Can be converted to proline.
c. Plays a major role in the urea cycle.
d. Is a precursor of putrescine, a polyamine.
e. Is in equilibrium with spermidine.

Back 27

e. Is in equilibrium with spermidine.

Front 28

S-Adenosylmethionine:
a. Contains a sulfonium ion that carries the methyl group to be transferred.
b. Yields α-ketobutyrate in the reaction in which the methyl is transferred.
c. Donates a methyl group in a freely reversible reaction.
d. Generates H2S by transsulfuration.
e. Provides the carbons for the formation of cysteine.

Back 28

a. Contains a sulfonium ion that carries the methyl group to be transferred.

Front 29

Lysine:
a. May be replaced by its α-keto acid analogue in the diet.
b. Produces pyruvate and acetoacetyl CoA in its catabolic pathway.
c. Is methylated by S-adenosylmethionine.
d. Is the only one of the common amino acids that is a precursor of carnitine.
e. All of the above are correct.

Back 29

d. Is the only one of the common amino acids that is a precursor of carnitine.

Front 30

Glutathione does all of the following except:
a. Participate in the transport of amino acids across some cell membranes.
b. Scavenge peroxides.
c. Form conjugates with some drugs to increase water solubility.
d. Decreases the stability of erythrocyte membranes.
e. Acts as cofactor for some enzymes.

Back 30

d. Decreases the stability of erythrocyte membranes.

Front 31

All of the following are true about the branched-chain amino acids except they:
a. Are essential in the diet.
b. Differ in that one is glucogenic, one is ketogenic, and one is classified as both.
c. Are catabolized in a manner that bears a resemblance to β-oxidation of fatty acids.
d. Are oxidized by a dehydrogenase complex to branched-chain acyl CoAs one carbon shorter than the parent compound.
e. Are metabolized initially in the liver.

Back 31

e. Are metabolized initially in the liver.

Front 32

Valine and isoleucine give rise to propionyl CoA, a precursor of Succinyl CoA. A disease related to a defect in this conversion is methylmalonic aciduria. Some patients respond to megadoses of vitamin B12. Which of the following statements about the conversion of propionyl CoA to Succinyl CoA is/are correct?
a. The first step in the conversion is a biotin-dependent carboxylation.
b. Some methylmalonic aciduria patients respond to B12 because the defect in the mutase converting malonyl CoA to succinyl CoA is poor binding of the cofactor.
c. The same pathway of propionyl CoA to succinyl CoA is part of the metabolism of odd-chain fatty acids.
d. All of the above are correct.
e. None of the above are correct.

Back 32

d. All of the above are correct.

Front 33

In the formation of urea from ammonia, all of the following are correct except:
a. Aspartate supplies one of the nitrogens found in urea.
b. This is an energy-expensive process, utilizing several ATP’s.
c. The rate of the cycle fluctuates with the diet.
d. Fumarate is produced.
e. Ornithine transcarbamoylase catalyzes the rate-limiting step.

Back 33

e. Ornithine transcarbamoylase catalyzes the rate-limiting step.

Front 34

Carbamoyl phosphate synthetase I:
a. Is a flavoprotein.
b. Is controlled primarily by feedback inhibition.
c. Is unresponsive to changes in arginine.
d. Requires N-acetyl glutamate as an allosteric effector.
e. Requires ATP as an allosteric effector.

Back 34

d. Requires N-acetyl glutamate as an allosteric effector.

Front 35

When there is a deficiency of phenylalanine hydroxylase:
a. Tyrosine hydroxylase substitutes for it so phenylalanine levels remain constant.
b. Tyrosine is synthesized by an alternate pathway instead of from phenylalanine.
c. Light skin and hair result because the enzyme catalyzes the first step to melanins.
d. Products derived from phenylalanine transamination are excreted.
e. Phenylalanine is catabolized by monoamine oxidase.

Back 35

d. Products derived from phenylalanine transamination are excreted.

Front 36

Catecholamines:
a. Production terminates with dopamine in the brain but epinephrine in the adrenal gland.
b. Production begins with the action of tyrosinase on tyrosine.
c. Are metabolized to both glucogenic and ketogenic fragments.
d. Are highly colored compounds.
e. All contain methyl groups donated by S-adenosylmethionine.

Back 36

a. Production terminates with dopamine in the brain but epinephrine in the adrenal gland.

Front 37

The two purine nucleotides found in RNA:
a. Are formed in a branched pathway from a common intermediate.
b. Are formed in a sequential pathway.
c. Must come from exogenous sources.
d. Are formed by oxidation of the deoxy forms.
e. Are synthesized from non-purine precursors by totally separate pathways.

Back 37

a. Are formed in a branched pathway from a common intermediate.

Front 38

The type of enzyme known as phosphoribosyltransferase in involved in all of the following except:
a. Salvage of pyrimidine bases.
b. The de novo synthesis of pyrimidine nucleotides.
c. The de novo synthesis of purine nucleotides.
d. Salvage of purine bases.

Back 38

c. The de novo synthesis of purine nucleotides.

Front 39

Uric acid is:
a. Formed from xanthine in the presence of O2.
b. A degradation product of cytidine.
c. Deficient in the condition known as gout.
d. A competitive inhibitor of xanthine oxidoreductase.
e. Oxidized, in humans, before it is excreted in urine.

Back 39

a. Formed from xanthine in the presence of O2.

Front 40

In nucleic acid degradation, all of the following are correct except:
a. There are nucleases that are specific for either DNA or RNA.
b. Nucleotidases convert nucleotides to nucleosides.
c. The conversion of nucleoside to a free base is an example of a hydrolysis.
d. Because of the presence of deaminases, hypoxanthine rather than adenine is formed.
e. A deficiency of adenosine deaminase leads to an immunodeficiency.

Back 40

c. The conversion of nucleoside to a free base is an example of a hydrolysis.

Front 41

The conversion of nucleoside 5’-monophosphates to nucleoside 5’-triphosphates:
a. Is catalyzed by nucleoside kinases.
b. Is a direct equilibrium reaction.
c. Utilizes a relatively specific nucleotide kinase and a relatively nonspecific nucleoside diphosphate kinase.
d. Generally uses GTP as a phosphate donor.
e. Occurs only during the S phase of the cell cycle.

Back 41

c. Utilizes a relatively specific nucleotide kinase and a relatively nonspecific nucleoside diphosphate kinase.

Front 42

Which of the following chemotherapeutic agents works by impairing de novo purine synthesis?
a. Acyclovir (acycloguanosine).
b. 5-fluorouracil (antimetabolite).
c. Methotrexate (antifolate).
d. Hydroxyurea.
e. AZT (3’azido-3’-deoxythymidine).

Back 42

c. Methotrexate (antifolate).

Front 43

Elements involved in the effectiveness of the dietary treatment include:
a. Conversion of exogenous uridine to UMP by uridine phosphotransferase.
b. UTP from exogenous uridine providing substrate for synthesis of CTP.
c. Inhibition of carbamoyl phosphate synthetase II by UTP.
d. All of the above.
e. None of the above.

Back 43

d. All of the above.

Front 44

In the de novo synthesis of pyrimidine nucleotides:
a. Reactions take place exclusively in the cytosol.
b. A free base is formed as an intermediate.
c. PRPP is required in the rate-limiting step.
d. UMP and CMP are formed from a common intermediate.
e. UMP inhibition of OMP-decarboxylase is the major control of the process.

Back 44

b. A free base is formed as an intermediate.

Front 45

The explanation for this difference in the two forms of gout is:
a. It is an experimental artifact and the decrease in uric acid and increase in xanthine plus hypoxanthine in non-Lesch-Nyhan gout is the same.
b. Allopurinol is less effective in non-Lesch-Nyhan gout.
c. There is an increased excretion of xanthine and hypoxanthine in non-Lesch-Nyhan gout.
d. PRPP levels are reduced in Lesch-Nyhan.
e. In non-Lesch-Nyhan gout hypoxanthine and xanthine are salvaged to IMP and XMP and inhibit PRPP amidotransferase.

Back 45

e. In non-Lesch-Nyhan gout hypoxanthine and xanthine are salvaged to IMP and XMP and inhibit PRPP amidotransferase.

Front 46

Which of the following is/are aspects of the overall regulation of de novo purine nucleotide synthesis?
a. AMP, GMP, and IMP shift PRPP amido transferase from a small form to a large form.
b. PRPP amidotransferase shows hyperbolic kinetics with PRPP.
c. AMP inhibits the conversion of IMP to GMP.
d. Change in glutamine concentration is a major regulator.
e. Direct interconversion of AMP to GMP maintains balance of the two.

Back 46

a. AMP, GMP, and IMP shift PRPP amido transferase from a small form to a large form.

Front 47

Which of the following statements is/are correct?
a. Methotrexate inhibits the de novo synthesis of UMP.
b. Arava inhibits the de novo synthesis of pyrimidine nucleotides.
c. Arava inhibits the conversion of dUMP to dTMP.
d. Methotrexate inhibits the production of tetrahydrobiopterin.
e. Both drugs greatly increase production of β-amino acids.

Back 47

b. Arava inhibits the de novo synthesis of pyrimidine nucleotides.

Front 48

Deoxyribonucleotides:
a. Cannot by synthesized so they must be supplied preformed in the diet.
b. Are synthesized de novo using dPRPP.
c. Are synthesized from ribonucleotides by an enzyme system involving thioredoxin.
d. Are synthesized from ribonucleotides by nucleotide kinases.
e. Can be formed only by salvaging free bases.

Back 48

c. Are synthesized from ribonucleotides by an enzyme system involving thioredoxin.