Protein Biochemistry 1

Question 1

examples of post-translational modification of amino acids

Answer 1

proline (prolyl hydroxylase) and lysine (lysyl hydroxylase) + vitamin C (ascorbate–> hydroxyproline and hydroxylysine –> collagen

Question 2

effect of lack of vitamin C

Answer 2

reduced hydroxylysine collagen cross-link formation –> reduced collagen strength (scurvy)

Question 3

Ubiquitin-proteasome system

Answer 3

ATP-dependent cross-linking of protein to ubiquitin –> sequestration to proteasome

Question 4

Lysosomal protein degradation

Answer 4

ATP INDEPENDENT. engulfs extracellular proteins/live pathogens –> breakdown via acid hydrolysis and cathepsins (lysosomal proteins)

Question 5

Function of Aminotransferases

Answer 5

transfer amino groups by converting one a-keto acid to its corresponding amino acid, and vice versa.

For degradation: move N to aspartate and ammonia for urea cycle

Question 6

Pyridoxal phosphate (PLP) function

Answer 6

derivative of Vitamin B6. used by aminotransferases to “hold”/transfer the amino groups

Question 7

Purpose of urea cycle

Answer 7

get rid of ammonia

Question 8

overall reaction in urea cycle

Answer 8

3ATP + HCO3- + NH4+ + aspartate –> 2ADP + AMP + 2Pi + PPi + fumarate + urea

Question 9

Where does the urea cycle take place?

Answer 9

partly in mitochondria, partly in the cytosol

Question 10

Two entry points for N in the urea cycle

Answer 10

1. Aspartate

2. Free ammonia (incorporated in carbamoyl phosphate)