Lecture 13: amino acid metabolism Flashcards
1
Q
Under what metabolic conditions do amino acids undergo oxidative degradation?
A
- When there are excess amino acids from the diet that aren’t needed
- When there are excess amino acids from normal physiological synthesis and the degradation of cellular proteins that aren’t needed
- Starvation/ diabetes –> carbohydrates are lacking/ not properly utilised –> AA undergo oxidative degradation to release energy
2
Q
What is the name of the enzyme that catalyses the conversion of an amino acid to an alpha keto acid?
A
Transaminase
3
Q
What is the name of the enzyme that catalyses the conversion of glutamate back to alpha ketoglutarate?
A
glutamate dehydrogenase
4
Q
How is glutamate dehydrogenase regulated?
A
- Allosteric regulation
- Activated when there’s low ATP/GTP
- inhibited where there’s high ATP/GTP/NADH
5
Q
Why is there a need to dispose off of ammonia?
A
- Toxic
- can cause brain edema
- raise pH of acidic cellular compartments
- exert osmotic effect
6
Q
Why is ammonia converted to urea?
A
- urea is neither basic or acidic
- it can be used as an osmolyte in the kidneys to reabsorb water and useful ions
7
Q
Where does the urea cycle take place?
A
liver
8
Q
Which organelles does the urea cycle take place?
A
Step 1-2: mitochondrial matrix
Step 3-5: cytosol
9
Q
How many steps are in the urea cycle?
A
5
10
Q
What happens to fumarate in the urea cycle?
A
- Fumarate is produced in step 4
- Fumarate –> malate –> oxaloacetate
- Oxaloacetate can directly enter the krebs
- It can be converted to pyruvate then acetyl coA then enter the krebs cycle
- It can undergo glucogenesis to produce glucose
- It can undergo transamination to give aspartate which then enters the urea cycle (step 3)
11
Q
How does arginine allosterically regulate the urea cycle?
A
- activates an acetylation reaction of glutamate which produces N-acetyl glutamate
- N acetyl glutamate allosterically activates carbamoyl phosphate synthetase 1, which catalyses the reaction in step 1.
