Unit 3 Digestion and Absorption

Question 1

Define digestion

Answer 1

• Hydrolysis of larger insoluble substances into smaller soluble substances that can be absorbed across cell membranes

Question 2

Which enzymes are involved in carbohydrate digestion and where are they found

Answer 2

• Amylase in salivary glands & Pancreas
  Membrane-bound disaccharides
• Maltase Sucrase & Lactase in small intestine

Question 3

What are the substrate and products of carbohydrate digestive enzymes

Answer 3

(POLYSACCHARIDE) Starch➜ (DISACCHARIDE) Maltose by amylase
Maltose➜(MONOSACCHARIDE) 2 Glucose molecules
Sucrose➜(MONOSACCHARIDE) Glucose + Fructose
Lactose➜(MONOSACCHARIDE) Glucose + Galactose
- Broken down by Hydrolysis of glycosidic bonds

Question 4

Which enzymes are involved in protein digestion and where do they act

Answer 4

TRYPSIN, CHROMOTRYPSIN(secreted by pancreas) - Small intestine
PEPSIN - Stomach
↑
Endopeptidases- Hydrolyse peptide bonds between amino acids in the middle of polymer chain
Exopeptidases - Hydrolyse peptide bonds between amino acids at the end of polymer chain
Membrane-bound dipeptidases - Hydrolyse peptide bonds between 2 amino acids

Question 5

What are the products of protein digestive enzymes

Answer 5

Endopeptidases hydrolyse to form➜
Shorter polypeptides/Increase no. of ends
Exopeptidases hydrolyse to form➜
Dipeptides/2 Amino acids
Membrane-bound Dipeptidases hydrolyse to form➜
Single amino acids which can move cross cell membrane

Question 6

Describe how lipids are digested.

Answer 6

• Bile salts produced by the liver emulsify fats to form small droplets so increase surface area for lipase action for hydrolysis
  THEN
• Lipase(Secreted by pancreas) in small intestine hydrolysis the ester bonds in lipids ➜ monoglycerides & fatty acids
• Forms micelles which are vesicles that contain bile salts and fatty acids
• Which make the fatty acids/monoglycerides more soluble in water

Question 7

Describe how lipids are absorbed into lymph vessels

Answer 7

1. Micelles are vesicles containing bile salts and fatty acids/monoglycerides
2. Which make the fatty acids/monoglycerides more soluble in water
3. Then release fatty acids/monoglycerides to
   cell lining of ileum
4. Fatty acids/monoglycerides absorbed by
   diffusion as small & non-polar into epithelial cells
5. Then modified into triglycerides by Golgi apparatus and combined with proteins to form
6. Vesicles which move to the cell membrane with chylomicrons

Question 8

Describe how amino acids and glucose are absorbed in digestion.

Answer 8

• Sodium ions are actively transported out of epithelial cells into bloodstream by carrier protein using hydrolysis of ATP
• So lower conc of sodium ions in epithelial cell than lumen so generates a concentration gradient for sodium ions from ileum into epithelial cell
  -Na+ ions move in by facilitated diffusion in co transporter bringing GLUCOSE or AMINO ACIDS with it against its concentration gradient

Question 9

Describe the adaptations of the villi in absorption.

Answer 9

Villi have very thin walls ➜ Creates a short diffusion pathway for absorption
Villi surrounded by a network of capillaries➜ Maintains concentration gradient for absorption
Millions of villi across ileum➜Creates a large surface area for absorption