Digestion And Absorption

Question 1

Starch digestion

Answer 1

• Amylase in saliva hydrolyses starch (by breaking the glycosidic bond)
to maltose (alpha glucose disaccharide)
• Amylase is denatured in the stomach – no carb digestion there
• Pancreatic amylase is released and further hydrolyses any leftover
starch
• Maltose is hydrolysed to α-glucose by breaking the glycosidic bond
in the ileum by the enzyme maltase which is a membrane-bound
enzyme
• Glucose is absorbed in co-transport

Question 2

Protein digestion

Answer 2

• Hydrolysis of peptide bonds.
• Endopeptidase act in the middle of protein/polypeptide in the
stomach and produces shorter polypeptides, increasing the number
of ends
• Exopeptidases act at end of protein/polypeptide and in the stomach
and produce dipeptides.
• Dipeptidases are membrane bound enzymes in the ileum which act
on dipeptides and produce single amino acids

Question 3

Lipid digestion

Answer 3

• Bile salts emulsify lipids into micelles to increase
surface area and solubility in water
• Lipids/triglycerides are hydrolysed by lipases to form
fatty acids and monoglycerides
• Micelles contain fatty acids, monoglycerides and bile
salts
• They move through the ileum to the epithelium cells

Question 4

Lipid absorption

Answer 4

• Micelles contain bile salts and fatty
acids/monoglycerides, making them soluble in water.
• Fatty acids/monoglycerides are released to cell/lining of the ileum.
• This maintains a higher concentration of fatty acids/monoglycerides outside the cell, so they are absorbed by simple diffusion.
• Triglycerides are reformed in cells and form chylomicrons.
• The chylomicron vesicles fuse with the cell membrane and are released by exocytosis.