17) What are zymogens? What are proenzymes? Describe three digestive system zymo
ID: 3519419 • Letter: 1
Question
17) What are zymogens? What are proenzymes? Describe three digestive system zymogens that are activated by different means. Explain the mode of activation of each, where they work, what they digest and the pH at which they do their jobs. Chymotrypsin, pepsin, carboxypeptidase, trypsin enzymes digest it and where? How is it absorbed and where? Which enzymes digest it and where? How is it absorbed and where? 18) Follow a protein molecule in food as it is digested from the stomach until its monomers reach the liver. Which 19) Follow a trigyceride molecule in food as it is digested from the stomach until its monomers reach the heart.Explanation / Answer
17. Zymogens: Zymogen is the inactive precursor of an enzyme which can be irreversibly transformed into an active enzyme when the covalent bond present in it is cleaved. Zymogens are also called as Proenzymes
Examples: (Please note that Enzymes action and their substrates are mentioned at the end of this question in the table)
Trypsinogen: Inactive form of trypsin. It is stored in pancreas but becomes active in the small intestine when the specific peptide bond in trypsinogen is cleaved by enteropeptidase.
Chymotrypsinogen: Inactive form of Chymotrypsin with one polypeptide chain and five disulphide bonds. It is also stored in pancreas but becomes active in the small intestine when the specific peptide bond in trypsinogen is cleaved by enteropeptidase.
Pepsinogen: It is the inactive form of pepsin which is activated by Hydrochloric acid in the stomach
Carboxypeptidases: Carboxypeptidases A and B are the proenzymes activated by trypsin in duodenum. Carboxypeptidase cleave polypeptides to amino acids.
Digestion of proteins:
18. Proteins are digested in the stomach, small intestine by pepsin, trypsin, chymotrypsin, carboxypeptidases A, B, Dipeptidases, tripeptidases, amino peptidases and the substrates and products are shown above in the table under DIGESTION OF PROTEINS.
Absorption: The proteins are absorbed in the form of amino acids from small intestine. The levo amino acids are actively absorbed by means of sodium co transport whereas the dextro amino acids are absorbed by means of facilitated diffusion. The absorption of amino acids is faster in duodenum and jejunum and slower in ileum. The proteins are then circulated to liver by hepatic portal vein which is responsible for transamination, deamination, remval of ammonia and urea cycle.
19.
Digestion of fats:
Gastric lipase
(weak lipase)
Digestion of triglyceride: Digestion, enzymes, areas of Gastrointestinal tract involved, substrates and products are shown above in the table above
Absorption: In the mucosal cells of intestine, most of the monoglycerides are converted to triglycerides. The triglycerides are also formed by re-esterification of fatty acids with more than 10-12 carbon atoms. The triglycerides and cholesterol esters are coated with layer of protein, cholesterol and phospholipids to form the particles called chylomicrons. Chylomicrons cannot pass through the membrane of the blood capillaries because of large particle size, so these lipid particles enter the lymph from blood
Fatty acids containing less than 10-12 carbon atoms enter the portal blood from mucosal cells and are transported as free fatty acids or unesterified fatty acids. Most of the fats are absorbed in upper part of small intestine. Bile is essential for fat absorption.
The free fatty acids are transported in the blood in combination with albumin and other lipids in the form of lipoproteins like Very low density lipoproteins (VLDL), High Density lipoproteins (HDL), Low density lipoproteins (LDL). LDL and HDL transport choesteol and phospholipids from to tissues and organs like heart and back to liver
Additional information:
Digestion of Carbohydrates:
Part Juice Enzyme Substrate End product Mouth Saliva No proteolytic enzyme --- ---- Stomach Gastric juice Pepsin Proteins Proteoses, Peptones, Large polypeptides Small intestine Pancreatic juice Trypsin Proteoses and peptones Dipeptides, tripeptides, polypeptides Chymotrypsin Carboxypeptidases A and B Dipeptides, tripeptides, polypeptides Amino acids Succus entericus Dipeptidases Dipeptides Amino acids Tripeptidases Tripeptides Amino peptidases Large polypeptidesRelated Questions
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