3.3 - Digestion and absorption

Question 1

Define digestion

Answer 1

Large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes

Question 2

Describe the digestion of carbohydrates by amylases and membrane-bound disaccharides

Answer 2

Amylase hydrolyses the glycosidic bond of starch molecule to form a disaccharide
Then membrane-bound disacharridase breaks down the disaccharide into monosaccharides

Question 3

Describe the digestion of lipids by lipase and bile salt action, as well as micelles in lipid absorption

Answer 3

Bile salts emulsify lipids into droplets to increase surface area for lipase action
Lipase hydrolyses ester bonds to produce glycerol and fatty acids
Micelles make monoglycerides more soluble and carry them to the lining of the ileum where they are absorbed by diffusion
Triglycerides are reformed in cells
Vesicles move to cell membrane

Question 4

Describe the digestion of proteins by endopeptidases, exopeptidases and membrane-bound dipeptidases

Answer 4

Endopeptidases - hydrolyse peptide bonds in the middle of polypeptide chain
Exopeptidases - hydrolyse peptide bonds at the end of the polypeptide chain
Dipeptidases - hydrolyse peptide bonds between 2 amino acids

Question 5

What do micelles contain?

Answer 5

Bile salts and monoglycerides

Question 6

Explain the advantages of lipid droplet and micelle formation

Answer 6

Droplets increase surface area of lipids
So faster hydrolysis of lipids
Micelles carry fatty monoglycerides to membrane

Question 7

Where are amylase and lipase produced and secreted?

Answer 7

Amylase - produced in pancreas, small intestine and salivary glands and secreted in mouth and small intestine
Lipase - produced in pancreas, secreted in small intestine