32 - Digestion of the proteins and absorption of the amino acids in gastrointestinal tract. Nitrogen balance and final excreted products of nitrogen metabolism. General reactions of amino acids metabolism – transamination, oxidative deamination, trans-deamination, decarboxylation. Biologically active amines (biogenic amines) – examples and function. Clinical significance of transaminases.

sections

• proteins

• physical digestion

• chemical digestion

• absorption

• oxidative deamination

• transamination

• decarboxylation

• oral box

• proteins

• chains of amino acids

• amino terminal + hydroxyl terminal

• physical digestionb

mouth

• chemical digestion

1. stomach → pepsinogen → pepsin

   • pepsin breaks down peptide bonds

   • stomach cells secrete pepsinogen in presence of food

   • simultaneously HCL is secreted, triggers conversion of pepsinogen to pepsin

2. Polypeptide enters small intestines

   • duodenum main site for digestion + absorption

   • pancreas secretes trypsinogen + chymotrypsin

   • enterokines convert trypsinogen → trypsin (hydrolyses polypeptide bonds, helps convert chymotrypsinogen)

   • large polypeptides are broken into small polypeptides

   • Brush border enzymes digest small polypeptides to amino acids

• absorption

1. small peptides absorbed through co-transporter with H+ then hydrolysed to amino acids

2. AAs carried theough blood to liver

3. AAs absorbed with Na+ then gets into blood

4. Leads to absorption of Na+ (by Na/K pump) so water also absorbed

5. AAs go into liver

• oxidative deamination

• removal of amine functional group + replacing it with ketone group

• Ammonia into urea cycle

• Occurs in glutamic acid as it is end product of transamination

• localised in liver

• transamination

• transfer of amine group of 1 molecule to another

• catalysed by transaminases

• results in transfer of amine group of one acids and ketone of another acid

• major keto acid - alpha KG

• decarboxylation

• splitting off of COOH as CO2

• Catalysed by - decarboxylases

• oral box