Protein Degradation

Question 1

Give the three mechanisms of muscle catabolism.

Answer 1

. Ubiquitin-proteosome system
. Autophagy via lysosome
. Calcium-activated proteases (calpains)

Question 2

How are amino acids catabolised to urea? Where does this take place?

Answer 2

. Remove nitrogen group from AA to form ammonium ions (via transamination and oxidative deamination)
. Ammonium ions enter urea cycle to produce urea
. This takes place in the liver

Question 3

What is the difference between essential and non-essential amino acids?

Answer 3

. Essential amino acids are obtained from the diet (can’t be synthesised by body)
. Non-essential amino acids can be synthesised or inter-converted

Question 4

What is positive nitrogen balance? When does this often occur?

Answer 4

. When nitrogen intake exceeds nitrogen excretion

. Occurs in growing children, pregnancy, and tissue repair following injury

Question 5

How is ammonium formed from amino acids?

Answer 5

. Transamination and oxidative deamination
. AA converted to glutamate by aminotransferase
. Glutamate converted to ammonium ions and α-ketoglutamate via oxidative deamination by glutamate dehydrogenase

Question 6

What is the difference between glucogenic and ketogenic amino acids?

Answer 6

. Glucogenic- their carbon skeletons increase the concentration of glucose
. Ketogenic- their carbon skeletons increase the concentration of ketone bodies