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1

Tay-Sach's disease is a lysosomal storage disease that will lead to accumulation of:
A. GM2 gangliosides
B. Glucocerebrosides
C. Sphingomyelin
D. Ceramide trihexosides
E. Galactocerebrosides

A. GM2 gangliosides

Tay Sachs: GM2 gangliosides; Gaucher: Glucocerebrosides; Fabry: Globosides;
Niemann-Pick: Sphingomyelin;
Farber: Ceramide;
Krabbe: Galactocerebrosides

2

Glutamine is the major source of ammonia excreted in the urine. What enzyme is responsible for the release of ammonia from glutamine?
A. Glutamine synthetase
B. Glutamine dehydrogenase
C. Glutaminase
D. Glutamine oxidase
E. Glutamine decarboxylase

C. Glutaminase

Glutaminase deaminates glutamine to produce ammonium ion (NH4+), which is excreted from the body. It is present in two tissues: Kidneys and Small intestine.

3

Ketoacidosis as seen in Type 1 DM can be explained by the following:
A. Decreased insulin, increased lipolysis, increased free fatty acid mobilization, increased ketogenesis
B. Decreased insulin, decreased lipolysis, increased free fatty acid mobilization, decreased ketolysis
C. Decreased glucagon, decreased lipogenesis, decreased free fatty acid mobilization, increased ketogenesis
D. Decreased epinephrine, increased lipolysis, decreased free fatty acid mobilization, increased ketogenesis
E. Increased glucagon, decreased lipolysis, increased free fatty acid mobilization, decreased ketolysis

A. Decreased insulin, increased lipolysis, increased free fatty acid mobilization, increased ketogenesis

Mechanism of diabetic ketoacidosis seen in type 1 DM: decreased insulin and increased glucagon/epinephrine-->increased lipolysis-->increased free fatty acids in plasma-->increased hepatic output of ketone bodies-->ketoacidosis.

4

Pyruvate, the end product of aerobic glycolysis is converted to acetyl CoA before it is used in the TCA cycle. The coenzymes required for this reaction includes the following, EXCEPT:
A. Thiamine pyrophosphate
B. Lipoic acid
C. Biotin
D. FAD
E. NAD

C. Biotin

The pyruvate dehydrogenase complex contains five coenzymes that acts as carriers or oxidants for the intermediates of the reaction converting pyruvate to acetyl CoA. This includes: 1) TPP 2) Lipoic acid 3) FAD 4) NAD 5) Coenzyme A.

5

In the presence of alcohol dehydrogenase, the rate of reduction of ethanol to acetaldehyde increases as you increase the concentration of acetaldehyde. Eventually, the rate of this reaction reaches maximum, where further increases in the concentration of ethanol have no effect. What is the reason for this?
A. All of the alcohol dehydrogenase enzymes are bound to ethanol
B. At high concentrations of ethanol, the activation energy of the reaction decreases
C. The enzyme alcohol dehydrogenase is no longer specific for ethanol
D. At high concentrations of ethanol, the change in free energy of the reaction decreases
E. The end product of this reaction is an inhibitor to alcohol dehydrogenase

A. All of the alcohol dehydrogenase enzymes are bound to ethanol

The rate of an enzyme-catalyzed reaction increases with substrate concentration until a maximal velocity (Vmax) is reached. The leveling off of the reaction rate at high substrate concentrations reflects the saturation with substrate of all available binding sites on the enzyme molecules present.

6

A beauty queen prepares joining the Ms. Universe Pageant by maintaining a fat-free diet. She is MOST likely to have deficiency in:
A. Triacylglycerol
B. Phospholipids
C. Vitamin B12
D. Folic acid
E. Prostaglandins

E. Prostaglandins

Prostaglandins are synthesized from arachidonic acid which in turn is synthesized from an essential fatty acid linoleic acid.

Linoleic acid is obtained by humans only from dietary lipids.

7

Dr. M recently passed the physician licensure exam, he celebrated by treating himself in an eat-all-you-can buffet restaurant. Which statement is TRUE during a well-fed state?
A. Glycogen phosphorylase is dephosphorylated and active
B. Pyruvate dehydrogenase is dephosphorylated and active
C. Hormone-sensitive lipase is phosphorylated and active
D. Acetyl-CoA carboxylase is phosphorylated and active
E. Glycogen synthase is phosphorylated and active

B. Pyruvate dehydrogenase is dephosphorylated and active

In the fed state, most of the enzymes involved in metabolism are in the dephosphorylated form and are active.

3 exceptions are: 1) glycogen phosphorylase kinase, 2) glycogen phosphorylase, 3) hormone-sensitive lipase of adipose tissue, these are inactive in their dephosphorylated state.

8

Essential fatty acid includes:
A. Gamma-linolenic acid
B. Oleic acid
C. Arachidic acid
D. Lignoceric acid
E. Linoleic acid

E. Linoleic acid

SIMILAR TO PREVIOUS BOARD EXAM CONCEPT PRINCIPLE: Essential fatty acids: 1) Linoleic acid, 2) Linolenic acid, 3) Arachidonic acid.

9

The enzyme involved in DNA replication which is responsible for removing supercoils in the helix?
A. Topoisomerase
B. Helicase
C. SSB proteins
D. Ligase
E. DNA polymerase

A. Topoisomerase

Helicase: unwinds the double helix;
SSB proteins: keep the two strands of DNA separated;
Ligase: seals the nick in the lagging strand by creating phosphodiester linkages;
DNA polymerase: elongates a new DNA strand by adding deoxyribonucleotides

10

The synthesis of folic acid from PABA is catalyzed by what enzyme?
A. Dihydrofolate reductase
B. Dihydrofolate synthetase
C. Dihydropteroate reductase
D. Dihydropteroate synthetase
E. Dihydrofolate dehydrogenase

D. Dihydropteroate synthetase

Dihydropteroate synthetase: PABA--->DHF;

Dihydrofolate reductase: DHF--->THF (active form of folic acid).

11

Avidin found in raw egg whites, inhibits fatty acid synthesis by binding this coenzyme.
A. Pyridoxal phosphate
B. Biotin
C. Tetrahydofolic acid
D. NAD
E. NADPH

B. Biotin

Biotin is used as cofactor for carboxylation reactions including the enzyme acetyl CoA carboxylase which is the rate limiting enzyme for fatty acid synthesis

12

High levels of the following inhibit the important enzymes involved in de novo purine synthesis, EXCEPT:
A. AMP
B. GMP
C. IMP
D. UMP
E. None of the above

D. UMP

The purine nucleotides including AMP, GMP, and IMP which are end products of de novo purine synthesis are inhibitors of the important enzymes involved in their synthesis.

UMP is a pyrimidine.

13

A deficiency in the enzyme tyrosine hydroxylase leads to decreased synthesis of the following, EXCEPT:
A. Dopamine
B. Norepinephrine
C. Epinephrine
D. Melanin
E. None of the above

D. Melanin

SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE: Tyrosine is the precursor of catecholamines using the enzyme tyrosine hydroxylase.

Melanin is synthsized from hydroxylation of tyrosine by tyrosinase.

14

The following statements are true for the rate-limiting reaction in porphyrin synthesis, EXCEPT:
A. Requires a coenzyme Vit. B6
B. The enzyme is δ-Aminolevulinic acid synthase
C. This reaction involves the condensation of Glycine and succinyl CoA
D. Occurs in the cytosol
E. This reaction is inhibited by accumulation of heme which is converted to hemin

D. Occurs in the cytosol

The initial and last three steps in the formation of porphyrins occur in the mitochondria, while the intermediate steps occur in the cytosol

15

During the fasting state:
A. There is increased glycogenesis
B. The activity of phosphoenolpyruvate carboxykinase (PEPCK) is decreased
C. There is decreased production of malonyl CoA
D. Lipoprotein lipase in the adipose tissues are active
E. In the first few days of fasting, there is decreased proteolysis

C. carboxykinase (PEPCK) is decreased

In the fasting state, there is increased glycogen degradation, increased gluconeogenesis, increased fatty acid oxidation. In the adipose, lipoprotein lipase activity is low. During the first few days of fasting, there is rapid breakdown of muscle protein.

16

A 7-month old boy had frequent infections often requiring hospitalizations. A family history indicated that the boy's mother had a brother with similar symptoms, and died at the age of 2 years old. Differential WBC count demonstrated complete lack of B and T cells. Which of the following statements are TRUE for this case?
A. The mainstay of treatment is blood transfusion
B. As dATP rises, ribonucleotide synthase is inhibited
C. The enzyme deficiency leads to low levels dATP
D. Adenosine deaminase is necessary for conversion of adenosine to inosine
E. Deficiency of the enzyme leads to severe common variable immunodeficiency

D. Adenosine deaminase is necessary for conversion of adenosine to inosine

The most common cause of autosomal recessive SCID is a deficiency of the enzyme adenosine deaminase (ADA) that leads to accumulation of deoxyadenosine and its derivatives, which are toxic to rapidly dividing immature lymphocytes.

17

Whcich pair of lipoproteins is a substrate of lipoprotein lipase?
A. Chylomicron and VLDL
B. Chylomicron remnant and IDL
C. VLDL and IDL
D. LDL and HDL
E. HDL and IDL

A. Chylomicron and VLDL

Chylomicrons and VLDL has Apo C-II which activates lipoprotein lipase.

18

Which statement is TRUE regarding the enzyme glucokinase?
A. found in most tissues
B. has high affinity for its substrate
C. inhibited by glucose-6-PO4
D. acts on glucose and other hexoses
E. has low Vmax

D. acts on glucose and other hexoses

Hexokinase: is present in most tissues, inhibited by glucose-6-PO4, has low Km and low Vmax;

Glucokinase: present only in liver and pacreas, inhibited by fructose-6-PO4, has high Km and high Vmax.

*BOTH can phosphorylate glucose and other hexoses.

19

Glucose is an epimer to what sugar at C4 position?
A. Mannose
B. Galactose
C. Ribose
D. Fructose
E. Arabinose

B. Galactose

Glucose and galactose are C4 epimers;

Glucose and mannose are C2 epimers

20

Essential amino acids cannot be synthesized by the body and must come from the diet. This includes the following, EXCEPT:
A. Isoleucine
B. Arginine
C. Tyrosine
D. Tryptophan
E. Lysine

C. Tyrosine

SIMILAR TO PREVIOUS BOARD EXAM CONCEPT/PRINCIPLE: Essential amino acids: "PVT TIM HALL, always ARGues, never TYRes"