Lecture 22 Flashcards
What does dietary protein provide?
dietary protein supplies amino acids to make body proteins (including important unsynthesysable ones), is a source of nitrogen for purines, pyrimidines and haems, the carbon skeletons can also be used as a fuel (producing urea from nitrogen).
What is kwashiokhor?
Kwashiokhor is a disease which results when a young child has been weaned off their mother and is no longer getting enough protein or missing some amino acids. They develop swollen bodies but their muscles degrade.
What are the essential amino acids?
The essential amino acids are leucine, isoleucine, lysine, methionine, threonine, phenylalanine, tryptophan and valine.
How does hydrolysis of proteins work and what hormones are involved?
Hydrolysis of proteins involves action of many enzymes (proteases) which break the protein down into smaller parts via cleavage of peptides. It starts in the stomach and is completed in the small intestine. Many hormones act to regulate activity of the enzymes involved to prevent self digestion e.g gastriin is secreted when protein containing food is in the stomach (stimulates gastric juice secretion). Secretin is produced by the duodenum when HCl is high (stimulating secretion of alkaline bile and pancreatic fluids. Cholecystokinin is produced by the duodenum when fats and amino acids are in the duodenum (stimulates release of pancreatic enzymes).
What are common enzymes in protein digestion and what are some examples of their action?
Enzymes involved in protein digestion are: pepsin, trypsin, chymotrypsin, carboxypeptidase (these three in pancreas), aminopeptidase and dipeptidase (these two in small intestine). Pepsin acts against aromatic (i.e Phe or Tyr), trypsin against positively charged (i.e Lys, Arg), chymotrypsin also acts against aromatic but is in a different location.
What are the two stages of protein digestion?
protein digestion occurs in two stages: the endopeptidases attack the peptide bonds within the peptide chain (e.g pepsin, trypsin, chymotrypsin), exopeptidases attack peptide bonds at the end of the chain and can either be aminopeptidases (act against amino terminal) or carboxypeptidases (carboxy terminal).
How are enzymes prevented from acting against the cells which secrete them?
They are inactivated until they come into contact with the activating compound (H+ for pepsinogen to convert it to pepsin (which can then convert other pepsinogens), the other enzymes are activated by location, via membrane bound enterokinase activating trypsinogen to trypsin which can then activate chymotrypsinogen and procarboxypeptidase).
What are some digestive diseases?
Pancreatitis is inflammation of the pancreas, caused by early activation of the pancreatic enzymes (trypsin, chymotrypsin and carboxypeptidase).
Cystic fibrosis causes malabsorption due to abnormally thick mucus causing pancreatic enzymes to be unable to move. Coeliac disease is an autoimmune disease which disrupts the function of the intestinal mucosa.
What order to peptidases act and how are the amino acids transported?
Protein digestion acts in this order: pepsin, trypsin, chymotrypsin, (carboxypeptidases and aminopeptidases), this leads to end products of amino acids as well as di and tri-peptides which are then broken down by di and tri-peptidases. These are then transported by sodium dependent amino acid transporters based on the chemical characteristics (neutral (Ala, Val, Phe), basic (Arg, Lys), acidic (Asp, Glu), other (taurine) and glycine, proline and hydroxyproline).
How are peptides absorbed?
Peptides are not absorbed much if longer than four amino acids, di and tri can be transported via cotransport with H+ ions via Pep T1 before being digested into amino acids by cytoplasmic peptidases. Absorption of intact proteins only occurs in a few circumstances (an example of which is newborn babies).
How does nucleic acid digestion occur?
nucleic acid digestion occurs heavily in the stomach due to weakness to acid hydrolysis, intestinal nucleases also help with hydrolysis.
