Biochem

Question 1

Deficiency in which enzyme causes orotic aciduria, a megaloblastic anemia that cannot be treated with Vit B12 or Folate supplementation, and has no hyperammonemia?

Answer 1

UMP synthase deficiency

Orotic aciduria

Uridine supplementation

Question 2

What enzyme is inhibited by hydroxyurea?

Answer 2

Ribonucleotide reductase

Pyrimidine synthesis pathway

Question 3

What enzyme is inhibited by 5-FU?

Answer 3

THymidylate synthase

Question 4

What enzyme is inhibited by MTX?

Answer 4

Eukaryotic Dihydrofolate reductase

Pyrimidine synthesis pathway

Question 5

What enzyme is inhibited by TMP?

Answer 5

Prokaryotic Dihydrofolate reductase

Pyrimidine synthesis pathway

Question 6

What immunologic disorder is caused by adenosine deaminase deficiency?

Answer 6

SCID (AR)

Question 7

What enzyme is absent in Lesch-Nyhan syndrome? What are the symptoms of this syndrome?

Answer 7

Enzyme: HGPRT def.

Sx:

• Hyperuricemia
• Gout
• Mental retardation
• Self-mutilation
• Choreoathetosis (dysTonia)

Question 8

What DNA repair enzyme is deficient in Bloom Syndrome?

Answer 8

Helicase

Question 9

What DNA repair enzyme is deficient in Xeroderma Pigmentosa?

Answer 9

Nucleotide excision repair

Repairs bulky helix-distorting lesions (pyrimidine dimers)

Question 10

Which DNA repair enzyme is deficient in HNPCC?

Answer 10

Mismatch repair

Question 11

Which DNA repair process is deficient in Ataxia Telangectasia?

Answer 11

Non-homologous end jointing

Question 12

Menkes disease causes a defect in which part of collagen synthesis?

Answer 12

Crosslinkage of lysine and hydroxylysine to form collagen fibrils.

Cu is deficient, but it is necessary for crosslinking (lysyl oxidase)

Question 13

What is the action and function of fomepizole?

Answer 13

• Action
  
  • Inhibits alcohol dehydrogenase
• Function
  
  • Prevent Methanol and ethylene glycol toxicity

Question 14

Which enzyme is inhibited by disulfiram?

Answer 14

Acetaldehyde dehydrogenase

Question 15

What is the limiting reagent of ethanol metabolism?

Answer 15

NAD+

Question 16

RLE of glycolysis

Answer 16

Phosphofructokinase-1 (PFK-1)

(+): AMP, 2,6 Bisphosphate

(-): ATP, Citrate (TCA)

Question 17

RLE Gluconeogenesis

Answer 17

Fructose 1,6 Bisphosphatase

(+) ATP, acetyl-CoA

(-) AMP, Fructose 2,6 bisphosphatase

Question 18

RLE TCA Cycle

Answer 18

Isocytrate Dehydrogenase

(+) ADP

(-) ATP, NADH

Question 19

RLE Glycogenesis

Answer 19

Glycogen Synthase

(+) Glucose-6-P, Insulin, Cortisol

(-): Epinephrine, Glucagon

Question 20

RLE Glycogenolysis

Answer 20

GLycogen phosphorylase

(+): Epinephrine, Glucagon, AMP

(-): Glucose-6-P, Insulin, ATP

Question 21

RLE: HMP shunt

Answer 21

Glucose-6-P Dehydrogenase (G6PD)

(+): NADP+

(-): NADPH

Question 22

RLE: De novo pyrimidine Synthesis

Answer 22

Carbamoyl Phosphate Synthetase II

Question 23

RLE: De novo Purine Synthesis

Answer 23

Glutamine-PRPP amidotransferase

(-): AMP, IMP, GMP

Question 24

RLE of Urea Cycle

Answer 24

Carbamoyl Phosphate Synthetase I

(+): N-acetylglutamate

Question 25

RLE: Fatty Acid Synthesis

Answer 25

Acetyl-CoA Carboxylase (ACC)

(+) Insulin, Citrate

(-) Glucagon, Palmitoyl-CoA

Question 26

RLE: Fatty Acid Oxidation

Answer 26

Carnitine acyltransferase I

(-) Malonyl-CoA

Question 27

RLE: Ketogenesis

Answer 27

HMG CoA Synthase

Question 28

RLE: Cholesterol Synthesis

Answer 28

HMG-CoA Reductase

(+): Insulin, Thyroxine

(-): Glucagon, Cholesterol