L17: Nitrogen Metabolism Flashcards
What is the amino acid pool?
Collection of free amino acids at low concs inside cells/blood stream. It includes mixing & exchange with other free amino acids around the body.
Why is protein needed in a diet?
No ‘storage’ form of protein in the body to replace amino acids & other N containing compounds.
Replace lost amino acids & allow tissue repair
Positive & negative nitrogen balance in terms of N intake & N excretion
Positive: N intake > N excretion
Negative: N intake < N excretion
Causes of positive nitrogen balance
1) Pregnancy
2) After immobilisation after accident
3) Recovering from serious illness
4) During normal growth in children
Causes of negative nitrogen balance
1) During illness
2) Starvation
3) Late stages of some cancer
4) Injury/trauma
Most cellular proteins degradation pathways
- Recognised as ‘old’ or damaged
- Removed by ubiquitin breakdown system
- Mixture of 20 amino acids
Foreign ‘exogenous’ proteins degradation pathways
- ‘Old’ or damaged sub-cellular organelles
- Taken into vesicles by endocytosis where vesicles fuse with lysosomes & proteolytic enzymes degrade proteins into amino acids
Define deamination
Removal of alpha-amino group
Where does deamination occur?
Liver mitochondrial matrix
What is deamination in this reaction
Glutamate -> a-Ketoglutarate + NH4+
catalysed by?
Glutamate dehydrogenase
Why does deamination remove the amino group from glutamate?
It can enter the Urea cycle for safe disposal
Define transamination
Conversion of 1 amino acid to another
Process of transamination
a-amino group is transferred from an amino acid to a-ketoglutarate to produce glutamate + a keto acid
Whhat is transamination catalysed by?
Aminotransferases/transaminases
What is
alanine + a-KG -> glutamate + pyruvate
catalysed by?
alanine aminotransferase
What is
aspartate + a-KG -> glutamate + oxaloacetate
catalysed by?
aspartate aminotransferase
Define transdeamination
Combined action of aminotransferases & glutamate to allow a-amino groups to enter Urea cycle
Transamination & deamination
Role of glutamine
Transport of ammonia in the blood
How many N in glutamate & glutamine?
Glutamate: 1N
Glutamine: 2N
What does the glucose-alanie cycle allow the liver to do?
Regenerate glucose from this alanine
Where and when is alanine generated?
Generated in skeletal muscle during exercise
What happens to glutamine that transports ammonia to liver?
Glutamine converted to glutamate + ammonia
What is alanie converted to from skeletal muscle?
Glutamate + Pyruvate
What is glutamate deaminated to generate?
a-ketoglutarate & ammonia
Which carbon skeletons can enter TCA cycle to generate ATP?
Pyruvate
Oxaloacetate
Fumarate
Succinul-CoA
a-Ketoglutarate
Which carbon skeletons can produce ketone bodies?
Acetoacetyl-CoA & Acetyl-CoA
Define essential amino acids
Cannot be synthesised in humans- must be obtained via diet
Role of glutamate
Central to amino acid degration
Role of glutamine
Transport ammonia to the liver
Role of alanine
Transport ammonia from skeletal muscle to the liver
