Amino Acid Metabolism

Question 1

What marks proteins for degradation ? What are the 3 enzymes ?

Answer 1

Ubiquitin
3 enzymes:
1. Ubiquitin activating enzyme
2. Ubiquitin conjugating enzyme
3. Ubiquitin protein ligase

Question 2

What is the N terminal rule ?

Answer 2

The amino acid sequence at the N terminal impacts half life of the protein

Question 3

What is the 26S proteasome ?

Answer 3

One ubiquitinated, the protein is turned into a proteasome.
The proteasome consists of a 20S catalytic core and a 19S regulatory cap.
S stands for svedburg unit, sedimentation coefficient.

Question 4

Explain deamination in AA metabolism

Answer 4

1. The first amino group is transferred to a keto group to produce glutamate. Catalysed by Transaminases. They all require pyridoxal phosphate which is the active form of vitamin B6.
2. Enzyme glutamate dehydrogenase catalyses the oxidative deamination of glutamate using NAD+ or NADH+ to form ammonia and alpha-ketoglutarate.

Question 5

What happens to the rest of the AA (carbon skeleton) after the amino group is removed ?

Answer 5

1. Glucogenic AA are converted into glucose via gluconeogenesis. Eg. Alanine into Pyruvate
2. Ketogenic AA are broken down into Acetyl-CoA which can be converted into fatty acids but not glucose

Question 6

How does the body remove ammonia after deamination ?

Answer 6

Via the urea cycle which converts ammonia into urea

Question 7

Describe the steps of the urea cycle

Answer 7

1. Ammonia combines with CO2 to produce carbamoyl phosphate. Requires 2 ATP.
2. Carbamoyl phosphate combines with Orthinine via enzyme Orthinine transcarbamoylase to form Citrulline.
3. Citrulline is converted into Argininosuccinate by adding Aspartate using the enzyme Argininosuccinate synthetase.
4. Argininosuccinate is split into Fumarate and Arginine using enzyme Argininosuccinase.
5. Arginine is converted into urea and Orthinine using enzyme Arginase.

Question 8

Explain the fate of fumerate ?

Answer 8

1. Back to aspartate and into the urea cycle
2. Into malate
3. Into Oxaloacetate

Question 9

What is the starting point for making all AAs ?

Answer 9

glutamate and glutamine

Question 10

How many pathways are there that make all amino acids ?

Answer 10

6 pathways

Question 11

What are non-essential AA ?

Answer 11

AA that we can make from other AA

Question 12

What are essential AA ?

Answer 12

One that the body cannot synthesise on its own. They must be obtained through the diet.

Question 13

What is high quality protein ?

Answer 13

Contains all essential amino acids, in the proportions they are required, in an easily digestible form