Amino Acid Metabolism

Question 1

How are proteins stored?

Answer 1

Proteins aren’t stored
It’s needed constantly to replace amino acids and N-containing compounds
Therefore a high protein intake is wasteful

Question 2

When is Nitrogen intake > N excretion?

Answer 2

When protein synthesis exceeds the rate of breakdown

Question 3

When is Nitrogen intake < N breakdown?

Answer 3

When the rate of breakdown exceeds synthesis

Question 4

How are proteins degraded?

Answer 4

Most cellular pathways - ubiquitin breakdown system
Foreign exogenous proteins - taken into vesicles and degraded by lysosomes and proteolytic enzymes
Muscle protein - starvation and hormones

Question 5

How to remove the N of an amino acid?

Answer 5

It can be removed by transfer to an acceptor molecule

Amino acid + 2-oxoglutarate -> oxo acid + glutamate

Question 6

What happens to Oxo-acids?

Answer 6

Most of the 20 amino acids become oxo acids after losing their amino group
They can then be metabolised in the TCA pathway to CO2 or H2O to provide and source of ATP

Question 7

What are ketogenic and glucogenic amino acids?

Answer 7

Ketogenic - can only be degraded to acetyl CoA
Glucogenic - they can be converted to glucose
Some amino acids are both

Question 8

What does the liver do in the nitrogen metabolism?

Answer 8

Removes amino acids, glucose and fats from blood supply
Absorbs amino acids for synthesis of cellular proteins
Synthesises plasma proteins, harm, purines and pyramidines
Degrades excess amino acids by transdeamination
Conversion of NH3 to urea

Question 9

What is the importance of glutamine?

Answer 9

Safe carrier of NH3 in blood
Glutamine can carry 2 ammonia equivalents to liver for urea formation
Can deliver ammonium ions to the kidney for pH regulation

Question 10

What are the end products of the urea cycle?

Answer 10

Urea - protein breakdown
Creatine - creatine phosphate breakdown
Uric acid - DNA/RNA breakdown
Ammonia - control of body pH