3.3 Digestion and Absorption

Question 1

What happens in digestion?

Answer 1

• Large insoluble molecules are hydrolysed into smaller soluble molecules
• Which can be absorbed across cell membranes

Question 2

How is starch digested in mammals?

Answer 2

• Amylase hydrolyses starch to maltose
• Maltase / membrane-bound disaccharides hydrolyses maltase to glucose
• Hydrolysis of glycosidic bond

Question 3

How are lipids digested in mammals?

Answer 3

• Bile salts emulsify lipids, increasing their surface area to volume ratio
• Lipase hydrolyses lipids to monoglycerides and fatty acids
• Hydrolysis of ester bond

Question 4

How are proteins digested in mammals?

Answer 4

• Endopeptidases hydrolyse internal bonds within a polypeptide (so more ends for exopeptidases)
• Exopeptidases hydrolysis terminal binds at ends of polypeptide
• Membrane-bound dipeptidases hydrolyse bonds between a dipeptide
• Hydrolysis of peptide bond

Question 5

How are monosaccharides and amino acids absorbed in mammals?

Answer 5

• Na+ is actively transported from the epithelial cell into the blood by the Na+/K+ pump
• Establishing a concentration gradient of Na+
• Na+ diffuses into the epithelial cell down its concentration gradient with monosaccharide/amino acid against its concentration gradient
• Via a co-transporter protein
• Monosaccharide/amino acid diffuses down its concentration gradient inti the blood by facilitated diffusion

Question 6

How are lipids absorbed in mammals?

Answer 6

• Bile salts combine with monoglycerides and fatty acids to form micelles
• Micelles make fatty acids soluble in water
• Micelles carry fatty acids to cell lining the ileum, maintaining a steep concentration gradient
• Fatty acids diffuse into epithelial cell
• Triglycerides reformed in cell