Metabolism of Proteins and Aminoacids

Question 1

Which of the following enzyme(s) is/are not involved in urea cycle
A. Glutamate dehydrogenase
B. Argininosuccinate synthetase
C. Alpha- ketoglutamate  dehydrogenase
D. Isocitrate dehydrogenase
E. Fumarase

Answer 1

Answer- A, C, D, E

Alpha ketoglutamate dehydrogenase, isocitrate dehydrogenase and fumarase are enzymes of Citric acid cycle

L glutamate dehydrogenase, deaminates L- glutamic acid to alpha-ketoglutaric acid and NH3.

Enzymes of urea cycle are
A. Carbamoyl phosphate synthetase I (rate limiting and pacemaker enzyme)
B. L- ornithine transcarbamoylase
C. Arginosuccinate synthase (defect l/t citrullinemia type I)
D. Arginosuccinate lyase (defect l/t arginosuccinic acidemia)
E. Arginase
F. N acetyl glutamate synthase
G. Mitochondrial membrane ornithine permeate
H. Mitochondrial aspartate/ glutamate carrier enzyme CTLN2 ( defect l/t citrullinemia type II)

Question 2

Urea cycle occurs in 
A. Liver 
B. GIT
C. Spleen
D. Kidney

Answer 2

Answer- A. Liver

Urea cycle occurs in liver and involves carbamoyl phosphate synthetase I (rate limiting and pacemaker enzyme), L- ornithine transcarbamoylase (brain lacks this), Arginosuccinate synthase (defect l/t citrullinemia type I), Arginosuccinate lyase (defect l/t arginosuccinic acidemia), Arginase (deficient in kidney and intestine and produce urea)

Question 3

A common feature of all serine proteases is
A. Autocatalytic activation of zymogen precursor
B. Tight binding of pancreatic trypsin inhibitor
C. Cleavage of protein on the carboxyl site of serine residues
D. Presence of Ser-His-Asp catalytic triad at active site

Answer 3

Answer-D. Presence of Ser-His-Asp catalytic triad at active site

Reference www.users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Series/serine_proteases.html
www.ebi.ac.uk/interpro/potm/2003_5/page1.html

Question 4

Vitamin B12 acts as coenzyme to which one of the following enzymes
A. Isocitrate dehydrogenase
B. Homocysteine methyl transferase 
C. Glycogen synthase
D. G-6-P dehydrogenase

Answer 4

Answer- B. Homocysteine methyl transferase

Vitamin B12 is required as coenzyme to Homocysteine methyl transferase involved in synthesis of methionine from homocysteine.