Metabolism of Proteins and Amino Acids

Question 1

Oxidation of this glycolytic intermediate leads to formation of serine.

Answer 1

3-phosphoglycerate

Question 2

Selenocysteine is required in several enzymes including:

Answer 2

Glutathione peroxidase
Deiodinase
Thioredoxin reductase

Question 3

The two amino groups of urea are derived from:

Answer 3

Ammonia

Aspartate

Question 4

Rate limiting step!

Urea cycle

Answer 4

Carbamoyl phosphate synthetase I
CO2 + NH3 > Carbamoyl phosphate
(2 ATPs)

Question 5

Immediate precursor of urea

Answer 5

Arginine

Question 6

Vitamin B6 deficiency can be diagnosed if excretion of xanthurenate is seen because B6 is a cofactor of this enzyme in amino acid catabolism.

Answer 6

Kynureninase

Involved in Tryptophan catabolism

Question 7

Heme protein Quiz!

1. Component of ETC
2. Oxidation of tryptophan
3. Degradation of H2O2
4. Hydroxylation of xenobiotics

Answer 7

1. Cytochrome c
2. Tryptophan pyrrolase
3. Catalase
4. Cytochrome P450

Question 8

Rate limiting step!

Heme synthesis

Answer 8

Formation of delta-aminolevulinic acid
ALA synthase
Reactants: Succinyl-CoA + Glycine
Co-factor: Pyridoxine

Question 9

This enzyme in heme synthesis is inhibited by heavy metal ion

Answer 9

ALA dehydratase

Question 10

Lead inactivates which enzymes in heme synthesis

Answer 10

ALA dehydratase

Ferrochelatase

Question 11

The only biochemical reaction in which CO is excreted as a byproduct.

Answer 11

Heme oxygenase

Heme > Biliverdin

Question 12

Drug that can increase activity of UDP-glucuronosyltransferase

Answer 12

Phenobarbital

Question 13

Rate limiting step!

Bilirubin metabolism

Answer 13

Secretion of conjugated bilirubin into bile

MRP-2 (multidrug resistance-like protein 2) aka Multispecific organic anion transporter

Question 14

Hyperbilirubinemia exists when blood bilirubin exceeds ___; but jaundice occurs when levels exceed ____.

Answer 14

1 mg/dL

2 - 2.5 mg/dL

Question 15

Differentiate retention hyperbilirubinemia from regurgitation hyperbilirubinemia.

Answer 15

Retention hyperbilirubinemia - Overproduction

Regurgitation hyperbilirubinemia - Reflux into bloodstream due to biliary obstruction

Question 16

Differentiate choluric jaundice from acholuric jaundice.

Answer 16

Choluria refers to presence of bile pigments (conjugated) in the urine.

Choluric: in regurgitation (direct)
Acholuric: in retention (indirect)

Question 17

Kernicterus occurs with bilirubin levels exceeding ___

Answer 17

20 - 25 mg/dL

Question 18

Normally, urine bilirubin is present. T/F

Answer 18

False! Urine urobilinogen may be seen but bilirubin (conjugated) is absent. It is only seen with direct hyperbilirubinemia.

Question 19

Normally, urobilinogen is present in the urine. T/F

Answer 19

True. Urobilinogen is found in trace amounts. Absent urobilinogen is seen in obstructive jaundice

Question 20

Increased urine urobilinogen and absent urine bilirubin suggests:

Answer 20

Hemolytic anemia