lipid and protein digestion

Question 1

describe the digestion of lipids in mammals, including the action of bile salts.

Answer 1

• bile salts (produced by liver) emulsify lipids to form smaller lipid droplets to increase the surface area of lipids for faster lipase activity.
• lipase (made in pancreas) hydrolyses lipids to form monoglycerides and fatty acids through hydrolysis of ester bonds.

Question 2

describe the digestion of protein in mammals.

Answer 2

• endopeptidase hydrolyses internal peptide bonds within a polypeptide, breaks larger polypeptides into two smaller polypeptides (so more ends/surface area for exopeptidase).
• exopeptidase hydrolyses external peptide bonds at the ends of the polypeptide (splits off one amino acid at a time) forming single amino acids.
• dipeptidase hydrolyse short peptides only 2 amino acids long through hydrolysis of peptide bonds.

Question 3

where is dipeptidase located?

Answer 3

on the brush border membranes of the small intestine.

Question 4

what does bile do?

Answer 4

binds to fat droplets and breaks it down into smaller fat droplets (emulsification) to increase the surface area for lipid digestion.

Question 5

what are micelles?

Answer 5

• glycerol, fatty acids, monoglyceride and bile salts form mixed micelles.
• they are made up of phospholipid tails, hydrophobic groups on the inside and hydrophilic groups on the outside.

Question 6

describe the absorption of lipids by a mammal, including the role of micelles.

Answer 6

• bile salts combine with monoglycerides and fatty acids to form micelles.
• monoglycerides and fatty acids are absorbed into epithelial cell via diffusion (as they are lipid soluble).

Question 7

what do micelles do?

Answer 7

(they are small enough to fit between microvilli on epithelial membrane) and so they allow the monoglycerides and fatty acids to be absorbed by the epithelial cells in the ileum.
- micelles make them more soluble in water and carry them to cells lining the ileum - maintains conc gradient.