Protein Digestion

Question 1

What is the process of protein digestion which occurs in the stomach?

Answer 1

• HCl denatures the proteins
• pepsin cleaves proteins into peptides
• the 5 pancreatic proteases secreted as proenzymes from the acinar cells of the exocrine pancreas breakdown proteins

Question 2

What the brush border peptidases?

Answer 2

there are many different types as the oligopeptides to be digested are extremely varied
have affinity for larger oligopeptides (3 – 8 amino acids)
either endopeptidases, or exopeptidases (comprising both aminopeptidases and carboxypeptidases)

Question 3

What are the absorption mechanisms of protein at the brush border?

Answer 3

There are 7
5 sodium dependent
2 sodium independent

Question 4

What are the absorption mechanisms of protein at the basolateral membrane?

Answer 4

there are 5
3 efflux of amino acids - sodium independent
2 influx of amino acids - sodium dependent

Question 5

Where do the H for the transport as the lumen of the duodenum and jejunum are slightly alkali?

Answer 5

Na/H exchanger provides a local gradient allowing H to move ‘downhill’ into the cells

Question 6

What digest the proteins to amino acids or oligopeptides in the lumen?

Answer 6

pepsin and pancreatic proteases

Question 7

How are oligopeptides broken down to amino acids?

Answer 7

peptidases at the brush border further hydrolyse them

Question 8

What are the 5 pancreatic proteases which act in the duodenum?

Answer 8

Trypsin 
chymotrypsin 
elastase
carboxypeptidase A
carboxypeptidase B

Question 9

How are di/tri/tetra peptides absorbed in the small intestine?

Answer 9

through a H dependent mechanism at the brush border - further hydrolysed in the enterocyte Na independent transport at the basolateral membrane

Question 10

How are amino acods transported across the apical membrane?

Answer 10

via a variety of amino acid transporters, some of which are Na+-dependent and others Na+-independent

Question 11

How are oligopeptides transported across the apical membrane?

Answer 11

by H+/oligopeptide co-transporter, PepT1

Question 12

What happens to oligopeptides within the enterocyte?

Answer 12

They are hydrolysed to amino acids by peptidases

Question 13

How do amino acids exit the enterocytes?

Answer 13

Across the basolateral membrane by several Na- independent transporters