Flashcards in Energy Storage - Protein Deck (31):
Where does stage 1 of the catabolism of protein occur?
In the GI tract
What happens during stage 1 of the catabolism of proteins?
Proteases and peptidases hydrolyse peptide bonds to release free amino acids. They are then absorbed into the circulation.
What can the amino acids be used for?
Synthesis of N containing compounds
What does it mean if an amino acid is ketogenic?
Once the amine group is removed, it's C skeleton can be converted to acetyl CoA which can go onto make ketone bodies
What does stage 2 catabolism of amino acids produce?
How much nitrogen is in the body of a 70kg man?
What does nitrogen leave the body as?
Urea, ammonia, creatinine, uric acid, urine.
Also lost in skin and hair.
When would someone have a positive N balance?
Growth, tissue repair, pregnancy, convalescence
When is there a negative N balance?
Starvation, trauma, malnutrition
List the 8 essential amino acids
Lysine, isoleucine, leucine, threonine, valine, tryptophan, phenylalanine, methionine
What happens to the excess amino acids?
Converted to intermediates of carbohydrate and lipid metabolism or oxidised to produce energy
What is the major site of the breakdown of amino acids?
What are the three common features of amino acid catabolism?
C atoms converted to intermediates of carbohydrate and lipid metabolism
Usually start with the removal of the amine group (transamination/deamination)
N atoms converted to urea
What stimulates transaminases?
Which two transaminases are clinically important and why?
Alanine aminotransferase (ALT/GPT)
Aspartate aminotransferase (AST/GOT)
Measured in serum to assess liver function
Which enzyme is normally deficient in phenylketonuria and and what does it normally do?
Oxidises phenylalanine to tyrosine
In PKU, what happens to phenylalanine when it accumulates in tissues? What effect does this have?
Metabolised to phenylpyruvate
It inhibits pyruvate uptake by mitochondria and interferes with energy metabolism in the brain.
-> inhibition of brain development
How is PKU diagnosed?
Detection of phenylketones in urine or measurement of blood phenylalanine concentration (normally less than 0.1mmol/L but can exceed 1mmol/L in PKU)
What type of inheritance is homocystinuria?
What is the deficient enzyme in homocystinuria and what does it normally do?
Normally converts homocysteine to cystathionine. This is further converted to cysteine.
What happens in homocystinuria?
Deficient CBS enzyme so homocysteine levels increase in the blood. Some is converted to methionine so this is increased. Homocystine (oxidised form) can be found in the urine.
What does homocystinuria cause?
Disorders of connective tissue, muscle, CNS and cardiovascular system. Can therefore be confused with Marfan's syndrome in children.
What is hyperammonaemia associated with?
Blurred vision, tremors, slurred speech, coma, death
How does ammonia get into the body?
Produced by many tissues and can be absorbed from the gut
What enzyme converts ammonia to glutamine and what else is needed?
Glutamate and ATP
What does glutaminase do?
Hydrolyses glutamine to ammonia and glutamate in the kidneys
How is the urea cycle regulated?
Enzymes are inducible.
High protein diet induces enzymes.
Low protein diet represses enzymes.
What does a deficient enzyme in the urea cycle cause?
-accumulation/excretion of a urea cycle intermediate
Symptoms of a deficiency in an enzyme of the urea cycle?
Irritability, vomiting, lethargy
Seizures, coma, death
How is a deficiency in one of the enzymes of the urea cycle treated?
Low protein diet