Amino Acid Metabolism Flashcards
What is the monomer of proteins ?
Amino acids
How are amino acids generated ?
They are generated by the digestion of proteins in the intestine and degradation of cellular proteins
Can excess amino acids be stored ?
Excess amino acids cannot be stored
Describe amino acid excretion
They are not directly excreted, the carbon skeleton is converted to central metabolic intermediates and the amino group is excreted
Describe the digestion and absorption of proteins
- protein digestion begins in the stomach as the acidic environment denatures proteins and pepsin degrades proteins
- further degradation takes place in the lumen of the intestine by pancreatic proteases and peptidases e.g. trypsin and aminopeptidases
Describe what happens to the amino acid pool in cells
- some amino acids are converted into proteins
- some amino acids are converted into nitrogen compounds
- surplus amino acids are split into the nitrogen amino group which is excreted and the carbon skeleton which is a fuel for energy
Describe events which require increased protein
during periods of growth :
- child
- adolescence
- pregnancy and lactation
during times of illness :
- trauma
- surgeries
- infection
Why are proteins needed in the oral cavity ?
- collagen : basis of tooth enamel, bone, dentine and cementum
- immunoglobulin A in saliva : resistance to infection
- mucin : prevent the formation of caries
- lysozymes : breakdown of food
What are the 2 types of amino acids ?
- essential amino acids must be supplied by the diet as they cannot be synthesised in the body
- non essential amino acids can be synthesised
Give some examples of essential amino acids
- arginine
- histidine
- methionine
Give some examples of non essential amino acids
- glutamate
- alanine
- asparagine
- proline
How is the amino group separated from glutamate ?
Glutamate + water + NADP+ > 2-oxoglutarate + NADPH + NH4+
- glutamate is oxidised and NADP+ is reduced
- this is done by the enzyme glutamate dehydrogenase
How is the amino group removed from other amino acids ?
- the amino group is transferred to 2-oxoglutarate by a transaminate enzyme causing it to turn into glutamate
- the amino group is then removed from glutamate by glutamate dehydrogenase to give 2-oxoglutarate
- the amino acid turns into a keto acid
- there is a free NH4+ group but it is toxic
What happens to the free amino group ?
- aquatic carnivores e.g. sharks will secrete excess nitrogen as free NH4+ because there is abundant water to disperse the NH4+ fast : ammoniotelic
- birds and terrestrial reptiles have a limited water intake and so they want to minimise water loss and therefore secrete excess nitrogen as a paste of uric acid crystals : uricotelic
- most terrestrial vertebrates secrete excess nitrogen as soluble urea : ureotelic
What is urea ?
- a small molecule
- rich in nitrogen which allows for little waste of other materials
- non toxic so may be accumulated before excretion
- highly soluble so can be excreted via urine
- no ionic charge so can accumulate without ionic perturbation
- it is produced in the urea cycle