Week 9 (protein metabolism) Flashcards
(49 cards)
Define catabolism
Breaking down complex compounds into simpler ones
Define anabolism
Building complex compounds from simpler ones.
What is metabolism?
Catabolism and anabolism combined
Explain the process of protein turnover
Proteins are turned over in the body all the time.
Old ones are broken down and new ones are made.
How many grams of protein turnover happens in a day in healthy individuals?
300-500g
What part of an amino acid makes up the ammonia?
Amino group
Which parts of an amino acid make up the carbon skeleton?
Side chain
Carboxyl group
What is the fate of amino acids?
Excess amino groups are excreted into urea.
The whole molecule is a building block for nitrogenous compounds.
The carbon skeleton is converted into metabolic intermediates.
Where are most amino acids metabolised?
Liver
What happens to ammonia?
Some ammonia generated is recycled and the rest is excreted via urea.
What happens to excess ammonia?
Excess ammonia generated in other tissues travels to liver to be metabolised.
Name the four amino acids in NH4+ metabolism
Glutamine
Glutamate
Alanine
Aspartate
How do carbon skeletons enter the citric acid cycle?
Via different intermediates
Describe glucogenic amino acids
Amino acids that can be converted into glucose and include most amino acids.
Describe ketogenic amino acids
Amino acids that can only be converted into acetyl-CoA and acetoacetyl-CoA.
Exclusively lysine and leucine
Why must essential amino acids be provided by the diet?
Essential amino acids cannot be synthesised by the body.
Can non-essential amino acids be synthesised by the body?
Yes - they can be synthesised by the body even under stress.
What is the first step in amino acid metabolism (transamination)?
NH4+ from one amino acid is transferred to alpha-ketoglutarate to make glutamate.
What is the effect of transamination?
NH4+ from many different amino acids are ‘collected; as glutamate.
Glutamate acts as NH4+ donor for biosynthetic/excretory pathways.
What is transamination catalysed by?
Aminotransferase (transaminase) enzymes.
Different aminotransferases for different amino acids.
Describe PLP
PLP is derived from vitamin B6.
It is a carrier of amino groups at the active site of aminotransferases.
PLP is covalently bound to the enzyme at the active site.
Name the two forms of PLP
Aldehyde = pyridoxal phosphate
Amine = pyridoxamine phosphate
Describe the transamination process
- amino acid substrate donates its amino group to pyridoxal phosphate at the active site of aminotransferase.
- that deaminated amino acid then leaves the active site, which now has pyridoxamine phosphate as a coenzyme.
- the second substrate, alpha-ketoglutarate, enters the active site.
- the amino group on pyridoxamine phosphate is then donated to alpha-ketoglutarate forming a glutamate, which can then dissociate from the active site.
- this leaves behind pyridoxal phosphate and an unoccupied active site ready to catalyse the next reaction.
What happens to glutamate in the liver?
Glutamate undergoes oxidative deamination in the liver.
In hepatocytes glutamate is transported from the cytosol to the mitochondria where it undergoes oxidative deamination.
Enzyme: glutamate dehydrogenase
Coenzyme: NAD+ or NADP+.
