Protein Metabolsim Flashcards
When proteins are broken down what is the process called?
Proteolysis
Briefly describe how protein is used to provide energy?
Depending on the side chains of an amino acid they will either be classified as glucogenic amino acids which can go through the process of gluconeogenesis or classed as ketogenic and will be used to produce ketone bodies, either way both result in energy.
There is also the amino groups to think about. This is converted quickly into urea which is then excreted in urine and does not play a role in energy production
Depending on whether an amino acid is glucogenic or ketogenic or both they will have different metabolic pathways, give an example of a pathway for each type.
Ketogenic: lysine
Converted to acetyl CoA and enters the kreb cycle
Glucogenic: alanine
Converted to pyruvate, converted to acetyl CoA and enters the kreb cycle
Both: phenylalanine
Converted to acetyl CoA and enters the the kreb cycle
In what situation is protein broken down to provide energy?
During extreme stress (starvation)
It is something that occurs under hormonal control
What effect does insulin and growth hormone have on protein synthesis and degradation?
Increase synthesis
Decreases degradation
What effect does glucocorticoids (eg cortisol) have on protein synthesis and degradation?
Decreases synthesis
Increases degradation
Excessive breakdown of protein can occur in Cushing’s syndrome, why does this happen and what effect does this have superficially?
Cushing’ is a syndrome where there is excess cortisol which promotes protein degradation. This weakens the skins structure leading to a striae formation. (Looks a little like stretch marks)
Some aminoacids can be synthesised in the body. Where do the carbon atoms come from?
Intermediates of glycolysis (C3)
Pentose phosphate pathway (C4/5)
Krebs cycle (C4/5)
Where are the amino groups from that go into making new amino acids?
From other amino acids-transamination
Or from ammonia
What are the two ways in which the nitrogen is removed from the amino acids?
Transamination-swapping the amine group with an oxygen of a keto acid.
Deamination- liberates amino group as free ammonia
Why is transamination sometimes beneficial?
It produces a better amino acid that can be dealt with more easily
What does alanine aminotranferase do?
ALT
Converts alanine to glutamate
What does aspartate aminotranferase do?
Converts glutamate to aspartate
How can plasma levels of ALT and AST be used?
They can indicate liver function
Levels of ALT and AST are particularly in high in condition where there is excessive cellular necrosis, give 3 examples of conditions in which this occurs?
Viral hep
Autoimmune liver disease
Toxic injury
Why does deamination occur in the liver and kidneys?
So that the ammonia can be dealt with straight away because it is very toxic
Why is deamination needed for dietary D-amino acids?
Because it cannot be metabolised in the form it is in. We need to deaminate it straight away
How is the urea cycle and transamination linked?
The glutamate and aspartate amino acids produced in transamination can be readily fed into the urea cycle which helps the body to convert the ammonia into urea
What is the purpose of the urea cycle?
It is a way of safely excreting amino acids.
The ammonia produced from deamination is used in the cycle and the glutamate and aspartate created in transamination can also be used.
The urea cycle occurs in the liver and is controlled by 5 enzymes. What does the amount of enzyme correlate to?
The need to dispose of ammonia
Ie lots of ammonia=lots of enzyme
High protein diet induces enzyme levels
And low protein diet/ starvation represses levels
**cycle is inducible but not regulated
What is the danger with refeeding syndrome?
The lack of protein has led to the down regulation of the enzymes needed for the urea cycle.
So giving lots of protein will overwhelm the liver and there is a risk of ammonia toxicity occurring
Genetic disorders and mutation can cause the complete lack and/or the partial loss of an enzyme in the urea cycle. What can this lead to? (2)
Hyperammonaemia
Accumulation/excretion of urea cycle intermediates
How can amino acids be used as fuel sources?
Converted to glucose or ketone bodies
