Question

List the sequence of structures that a single amino acid (initially in a protein molecule that you eat) goes through from the moment it passes your lips to when it ends up in a hepatocyte. Then explain what (if any) chemicals relevant to digestive physiology it is exposed to at each step and what happens to the protein and eventually protein fragments each step of the way.

Answer 1

Sequence of structures that a single amino acid travels from lips to hepatocyte

Lips ----oral cavity  -------esophagus ------stomach -----Small intestine -------Intestinal lining-------hepatocyte of liver

Protein molecules enters through the mouth and travels through the structure called esophagus (long food pipe) and reaches to the stomach. In the stomach the digestion of protein begins,the protein molecules get denatured by the secretion of pepsin and Hcl from the stoamch wall. The pepsin breaks down the protein into smaller fragments that is called smaller polypeptides and amino acids.Now food mixed with the gastric juices is termed as chyme .

Thus the chyme travels via the pyrolic sphincter to the small intestine,at the same time pancreas starts secreting bicarbonate to neutralize the acidity of chyme and protects the lining of small intestine.Hence,the small intestine produces the hormone named as secretin and cholecystokinin which helps in digestion of protein further.The secretin hormone triggers the socdium bicarbonate secretion from the pancreas.

The major enzymes secreted by the pancreas helps in protein digestion, it secrets the trypsin,chymotrypsin and elastase to accelerate the protein digestion.Now digested small amino acids get transported to the intestinal mucosal lining and generate the new proteins. The pancreas produces the trypsin,chymotrypsin when the enterokinase enzyme is present at small intestinal lining.The enterokinase helps in converting the inactive trypsinogen to trypsin followed to that trypsin helps in conversion of chymotrypsinogen to chymotrypsin.Thus the active trypsin and chymotrypsin takes part in proteolysis and produces the smaller amino acids.The smaller amino acis travesl to the apical surface of intestinal mucosae by the help of sodium -amino acid transporter.

After transportation through the mucosal lining, the amino acid and sodium get released at the basal surface of the mucosal lining.The sodium gets recycled in the transporter complex and amino acid are released into the bloodstream and travels to the hepatocytes of liver and cells, then finally transfers all round the body for protein synthesis.