Digestion & Absorption Of Proteins

Question 1

Name 3 peptidases present in pancreatic secretion

Answer 1

1. Trypsin (trypsinogen)
2. Elastase (proelastase)
3. Carboxypeptidase A/B (procarboxypeptidase)

Question 2

Name 3 peptidases that are present in the small intestinal brush border

Answer 2

1. Enteropeptidase
2. Aminopeptidase
3. Dipeptidase

Question 3

List the factors that impair protein digestion in the stomach

Answer 3

1. pH
2. Activity of enzymes (pepsin)
3. Amount/state of protein

Question 4

List the mechanisms that prevent auto digestion of the pancreas by its own proteolytic enzymes

Answer 4

1. Pancreatic enzymes are synthesized & secreted as inactive zymogens
2. Enterokinase is an enzyme on the luminal surface of the brush border membrane
3. It converts inactive trypsinogen into active trypsin which is the common activator of all other pancreatic enzymes
4. Trypsin inhibitor secreted by pancreatic acinar cells safeguards against trypsin activation within the pancreas
5. Autolysis by trypsin
6. Fluid secretion by duct cells to flush zymogens or active enzymes out of pancreas and into duodenum

Question 5

State the significance of maintaining different pH values at different segments along the gastrointestinal tract

Answer 5

1. Saliva in mouth has pH of 6.5-7.5 (optimum level for salivary amylase); neutralizes any gastric reflux into esophagus
2. Gastric juice in stomach has pH of 1.5-4.0; for activation of pepsinogen to pepsin; + for gastric lipase
3. Duodenum has pH of 7-8.5 (optimal for pancreatic + brush border enzymes)
4. Small intestine has pH of 6-7 (optimal for brush border enzymes)
5. Large intestine has pH of 4-7; protects gut flora which develops the full functioning of the immune system

Question 6

How does a deficiency in dipeptidases and tripeptidases affect protein digestion?

Answer 6

1. Pepsin, trypsin, chymotrypsin, elastase are endopeptidases
2. Proteolytic enzymes ( di & tri peptidases) in the brush border + aminopoptidases secreted by intestinal mucosal cells
3. Hydrolyses terminal peptide bonds and releases AAs which are absorbed into blood
4. Transported to liver by portal circulation
5. Deficiency of brush border enzymes of intestinal mucosal cells (di & tri peptidases) impairs release of AAs
6. } Affects protein digestion

Question 7

Explain how protein digestion in the small intestine is affected in patients with immune mediated mucosal damage of the duodenum

Answer 7

1. In the stomach, HCl denatures proteins & pepsin breaks proteins into large polypeptides
2. In SI, proteins are digested by proteolytic enzymes in pancreatic juice + enzymes by brush border
3. proteolytic enzymes in pancreatic secretions are secreted to duodenum as inactive forms ( trypsinogen, chymotryspsinogen, procarboxypeptidase,proelastase )
4. Enterokinase is secreted by mucosa of SI & activates trypsinogen → trypsin. Further, chymotrypsinogen → chymotrypsin & procarboxypeptidase → carboxypeptidase
5. Immune mediated damage to duodenal mucosa impairs release of enterokinase
6. This prevents activation of proteolytic enzymes, so proteins remain undigested + they cannot be absorbed into duodenum & so they pass out in feces
7. SI also secretes aminopeptidases, dipeptidases, tripeptidases which split small peptides into AAs
8. Damage to mucosa impairs secretion of these enzymes too

Question 8

List eight proteolytic enzymes in the human GI tract

Answer 8

1. Pepsin
2. Trypsin
3. Chymotrypsin
4. Elastase
5. Carboxypeptidase A
6. Carboxypeptidase B
7. Aminopeptidase
8. Dipeptidase

Question 9

Digestion of proteins involves many enzymes, however starch or triglycerides are digested by a single enzyme.
Explain the biochemical basis of this statement

Answer 9

1. Write about protein digestion & its many enzymes
2. Starch is a large polysaccharide present in potatoes and different types of grains
3. When food is chewed, it is mixed with saliva; saliva contains ptyalin, an alpha amylase secreted by the parotid gland (pancreatic amylase also digests starch)
4. Amylases can breakdown starch into maltose and other small polymers of glucose
5. Starch digestion requires only amylase
6. Triglycerides are neutral fats in the diet
7. They are digested in the stomach by lingual lipase
8. In the duodenum, they are emulsified by bile salts and by the peristaltic action of the intestines
9. Emulsified bile is digested by pancreatic lipase into fatty acids and monoglycerides
10. Triglyceride digestion requires only lipase