MEH: Protein Metabolism Flashcards
What molecule is used as an estimate of muscle mass?
Creatinine (it is the breakdown product of creatine and creatine phosphate)
What is positive nitrogen balance?
When the intake of protein is greater than the output.
It is a normal state in growth and pregnancy or in an adult recovering from malnutrition.
What is negative nitrogen balance?
When intake is greater than output.
This is never physiologically normal.
Give an example of a ketogenic amino acid.
Lysine
Leucine
Give an example of a glucogenic amino acid.
Alanine
Glycine
Define ketogenic amino acid.
An amino acid this is degraded directly into acetyl-CoA, which is the precursor of ketone bodies.
Define glucogenic amino acid.
An amino acid which is converted into glucose.
What is protein turn over?
The balance between protein synthesis and protein degradation.
What is Cushing syndrome?
A condition wherein there is excessive breakdown of protein due to excess cortisol. It present clinically as weakened skin which leads to striae formation.
What is transamination?
Swapping the amine group of one amino acid for the oxygen on a keto acid.
Name 2 aminotransferase enzymes.
- ALT (Alanine aminotransferase)
2. AST (Aspartate aminotransferase)
What does ALT transfer?
Alanine to glutamate
What does AST convert?
Glutamate to aspartate
What is deamination?
Liberates amino group as free ammonia.
How is toxic ammonia removed?
Converted into urine and then directly excreted in urine.
What do defects in the urea cycle lead to?
Partial loss of enzyme function which leads to…
- Hyperammoneamia
- Accumulation/ excretion of urea cycle intermediates
What symptoms are related to defects in the urea cycle?
- Vomiting
- Lethargy
- Irritability
- Mental retardation
- Seizures
- Coma
Describe 2 mechanisms by which ammonia can be disposed of.
- Glutamine: Ammonia combines with glutamate to form glutamine. It is transported in the blood to the liver where glutaminase reforms glutamate and ammonia. This is fed into the urea cycle.
- Alanine: Ammonia combines with pyruvate to form analine. An alien is transported in the blood to the liver where it is converted back to pyruvate though transanimation. Amine group fed into urea cycle, pyruvate undergoes glucogenisis and is fed back to tissues.
What is PKU (phenylketonuria) as a result of?
Deficiency in phenylalanine hydroxylase
What are the clinical consequences of PKU?
- Accumulation of phenylalanine in the blood
- This undergoes transaamination which produces phenylketones
- Molecules such as noradrenaline and dopamine also cannot be synthesised.
What is homocystinurias and what is it as a result of?
- Problem in breaking down methionine
- Defect in cytathionine beta-synthase
What does homocystinurias affect?
- Connective tissue
- Muscles
- CVS
