Lecture 5 Nitrogen metabolism: amino acids Flashcards
Why do we need protein in our diets?
To supply us with amino acids, essential amino acids can only be derived from the diet, they cannot be synthesised. There is also a constant turnover of protein so nitrogen ingestion is necessary.
Can the body metabolise N2?
No, so we must eat proteins to get nitrogen.
What is nitrogen needed for in biosynthesis?
Proteins
Nucleotides
Nucleic acids
What is deamination?
The release of an amino group from an amino acid.
Describe the steps in transamination, use glutamate as an example.
Deamination is done by the enzyme glutamate dehydrogenase which converts glutamate into NH3 and alpha-ketoglutarate. This in the mitochondria and requires the reduction of NAD(P)+ to NAD(P)H.
It is readily reversible.
What is transamination?
It is the transfer of an amino group from an amino acid to a keto-acid.
What is aminotransferase?
it is the enzyme used during transamination.
What is pyridoxal phosphate?
It is a coenzyme used by aminotransferase during transamination.
Why is alpha-ketoglutarate a ‘common acceptor’ of amino groups?
It often accepts amino groups and forms glutamate which can in turn be reconverted by glutamate dehydrogenase. Glutamate and glutamine are the sources of most of the amino groups for transamination.
How are non-essential amino acids formed by transamination?
Amino group from glutamate is transferred to intermediates of glycolysis or CAC to form new amino acids.
Explain the glutamine-glutamate cycle?
Glutamate is formed by adding an amino group to alpha-ketoglutarate by glutamate synthetase. Glutamate can take another amino group and become glutamine, this is done by glutamine synthetase. Glutamine can be deaminated by glutaminase to yield an amino group and glutamate. This ability to carry amino groups makes the molecules ideal carriers to distribute amino groups through transaminations.
In what three circumstances are amino acids catabolised?
Normal synthesis and degradation of proteins.
In a protein-rich diet.
In starvation or uncontrolled diabetes mellitus.
What is the first step in amino acid catabolism?
Removal of amino group by a dehydrogenase.
Explain the glucose alanine cycle.
Alanine is just pyruvate with an added amino group.
Therefore glucose and alanine can be converted to each other through glycolysis and transamination.
Glutamate can transaminate pyruvate yielding alanine and alpha-ketoglutarate.
Alpha-ketoglutarate can transaiminase with alanine yielding pyruvate and glutamate.
The cycle is used to transfer ammonia within alanine from the muscles to the liver where it can be converted to ammonia then urea for excretion.
What are the 3 excretable forms of ammonia for animals?
Ammonia for ammonotelic animal: aquatic vertebrates such as bony fish.
Uric acid for Uricotelic animals: birds and reptiles.
Urea for ureotelic animals: terrestrial vertebrates, also sharks.
