Amino Acid Metabolism

Question 1

What is the Main Site of Degradation?

Answer 1

liver

Question 2

Simply, How does Degradation Happen in the stomach, intestine and blood?

Answer 2

stomach
- low pH denatures pepsin and proteins

intestine
- amino peptides released

blood
- transports amino acids to liver

Question 3

In Detail, how does Degradation work? ubiQUITin

Answer 3

• Ubiquitin is a biological tag
• activated by attachment to enzyme 1
• transfers to enzyme 2
• enzyme 3 transfers Ubiquitin to target protein
• reads n terminal
• determines which resides are to be saved or degraded

Question 4

What are the Stabilising Residues which Save the Protein

Answer 4

serine
alanine
glycine

Question 5

What are the Destabilising Residues which Degrade the Protein

Answer 5

arginine
tryptophan
phenylalanine

Question 6

What are 2 Pathways of Degradation

Answer 6

endocytosis
autophagy

Question 7

What are 2 Ways to Dispose of Nitrogen from the Liver?

Answer 7

transamination
transdeamination

Question 8

Describe Transamination

Answer 8

uses aminotransferases to catalyse the transfer of amino group to a a-ketoacid
- requires pyridoxal phosphate as a cofactor
- derivative of B6

product = new amino acid and a new a-keto acid

Question 9

Describe Transamination in steps

Answer 9

TRANSFERRING AMINO ACID TO A-KETOACID
1. pyroxidal phosphate is attached to lysine via covalent bond
2. the active site = Schiff-base
3. amino acid displaces the lysine
4. = amino acid and pyroxidal phosphate
5. remove a proton = quinoid intermediate
6. add hydrogen = ketimine
7. add water = a-ketoacid and pyridoxamine phosphate

Question 10

Describe Transdeamination

Answer 10

a transamination coupled to an oxidative deamination, requiring glutamate

Question 11

Describe Transdeamination in Steps

Answer 11

• amino group from glutamate is removed and transferred to ketoacid
• = new amino acid + different ketoacid
• enzyme = glutamate dehydrogenase
• NH4 ammonia is generated as a byproduct
• ammonia converted into urea through urea cycle to remove it

Question 12

What is the Equation for Urea?

Answer 12

CO2 + NH4+ = Urea

Question 13

Draw the Ornithin Cycle. What does it Recycle and where does it occur?

Answer 13

Bicarbonate converts into
Carboxyphosphate, converts into
Carbamic Acid, converts into
Carbomyl Phosphate.
Orthinine is added.
These both make:
Citrulline.
Aspartate is added.
These both make:
Arginosuccinate, converting into:
Arginine and Fumurate.
Arginine makes
Urea and Orthinine

Recycles - regenerated orthinine carries
Occurs in - liver hepatocytes, first 2 steps in mitochondria, last 3 in cystol

Question 14

How is Urea Cycle Regulated?

Answer 14

controlled by N-Acetylglutamate
- allosterically activates Carbomyl Phosphate Synthetase I

Question 15

Why is Ammonia Toxic?

Answer 15

hyperammonaemia
- blurred vision, speech and tremors

high conc
- coma, brain damage, death

Question 16

How is Ammonia Toxic?

Answer 16

more glutamate formation
less a-ketogluturate
= reduced TCA
= less energy for large organs

Question 17

What is a Common Genetic Deficiency of the Urea Cycle?

Answer 17

Ornithine transcarbamylase deficiency
= hyperammonaemia and irreversible mental retardation

Question 18

An Environmental Factor Creating an Error in the Urea Cycle

Answer 18

liver cirrhosis

Question 19

How do you Treat Excess Glycine and Glutamine

Answer 19

Glycine = Benzoate, excrete Hippurate

Glutamine - Phenylacetate, excrete Phenylacetylglutamine