Digestion & Absorption

Question 1

Describe the role of enzymes in the digestion of proteins in a mammal
(Endo,exo,peptid)

Answer 1

• Hydrolysis of peptide bonds by peptidases
• Endopeptidase produces short polypeptides
• Exopeptidase produces dipeptides
• Dipeptidase produces single amino acids

Question 2

Explain what happens in digestion (Large to small)

Answer 2

• Large insoluble biological molecules are hydrolysed into smaller soluble molecules
• That are small enough to be absorbed across cell membranes into blood

Question 3

Describe the digestion of disaccharides in mammals
(disaccharidases, maltose, sucrose, lactose, hydrolysis)

Answer 3

• Membrane bound disaccharidases hydrolyse disaccharide into 2 monosaccharides
• Maltase hydrolyses maltose into glucose & glucose
• Sucrase - Hydrolyses sucrose into glucose and fructose
• Lactase - Hydrolyses lactose into galactose and glucose
• Hydrolysis of glycosidic bond

Question 4

Describe the digestion of lipids in mammals, including the action of bile salts

Answer 4

• Bile salts (produced by the liver) emulsify lipids causing them to form smaller lipid droplets
• This increases the surface area of the lipids for faster lipase activity
• Lipase (made in pancreas) hydrolyses lipids (e.g Triglycerides -> Monoglycerides + Fatty Acids
• Hydrolysis of Ester Bonds

Question 5

Describe the digestion of proteins by a mammal

Answer 5

Endopeptidases hydrolyse INTERNAL peptide bonds in a polypeptide into smaller peptides
- Increases surface area for exopeptidases
- Exopeptidases hydrolyse terminal peptide bonds at ends of polypeptides into single amino acids
- Membrane bound dipeptidases hydrolyse peptide bond between 2 amino acids
- Hydrolysis of peptide bond

Question 6

Suggest why membrane bound enzymes are important in digestion

Answer 6

• Membrane bound enzymes are located on cell membranes of epithelial cells lining the ileum
• (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption)

Question 7

Describe the pathway for absorption of products of digestion in mammals (LIB)

Answer 7

Lumen (inside of ileum) -> Cells lining ileum (part of small intestine) -> Blood

Question 8

Describe the absorption of lipids by a mammal, including the role of micelles
(bile salts, solubility, concentration of fatty acids, globules, chylomicrons, vesicles)

Answer 8

● Micelles contain bile salts, monoglycerides and fatty acids
○ Make monoglycerides and fatty acids (more) soluble in water
○ Carry / release fatty acids and monoglycerides to cell / lining of ileum
○ Maintain high concentration of fatty acids to cell / lining
● Monoglycerides / fatty acids absorbed (into epithelial cell) by diffusion (lipid soluble)
● Triglycerides reformed in (epithelial) cells and aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and leave via exocytosis
○ Enter lymphatic vessels and eventually return to blood circulation

Question 9

Describe the digestion of carbohydrates in mammals

Answer 9

• Digestion takes place in mouth & small intestine
• Amylase (produced in saliva) hydrolyses starch into maltose
• Maltose (a disaccharide) is hydrolysed by maltase (a disaccharidase produced in small intestine) into 2 glucose molecules
• Lactase & Sucrase also present
• Hydrolysis of glycosidic bonds
• Monosaccharides absorbed into small intestine, then pass into blood stream