Digestion and absorption

Question 1

process of digestion of starch by amylases and membrane-bound disaccharidases.

Answer 1

Amylase hydrolyses starch to maltose
Amylase produced by salivary glands, released into mouth
Amylase produced by pancreas, released into small intestine
Membrane bound maltase (attached to epithelial cells lining the ileum of the small intestine) → hydrolyse maltose to glucose

Hydrolysis of glycosidic bond

Question 2

the process of digestion of dissacharides.

Answer 2

Membrane bound disaccharidases, e.g. maltase, sucrose, lactase (attached to epithelial cells lining the ileum of the small intestine) → hydrolyse disaccharide to x2 named monosaccharides

maltase – maltose → glucose + glucose
sucrase – sucrose → fructose + glucose
lactase – lactose → galactose + glucose

Hydrolysis of glycosidic bond

Question 3

digestion of lipids

Answer 3

Bile salts produced by the liver
Bile salts emulsify lipid to smaller lipid droplets
Increasing surface area (to volume ratio) of lipids speeds up action of lipases
Lipase made in the pancreas, released to small intestine
Lipase hydrolyses lipids → monoglycerides + fatty acids
Breaking ester bond
Monoglycerides, fatty acids and bile salts stick together to form micelles

Question 4

digestion of proteins

Answer 4

Endopeptidases:
Hydrolyse peptide bonds within a protein / between amino acids in the central region
Breaking protein into two or more smaller peptides

Exopeptidases:
Hydrolyse peptide bonds at the ends of protein molecules
Removing a single amino acid

Dipeptidases:
Often membrane bound in ileum
Hydrolyse peptide bond between a dipeptide = 2 amino acids

Question 5

Describe the mechanism for absorption of monosaccharides and amino acids by the cells lining the ileum. (co-transport)

Answer 5

1)Sodium ions actively transported out of epithelial cells lining the ileum, into the blood, by the sodium-potassium pump. Creating a concentration gradient of sodium

2)Sodium ions and glucose move by facilitated diffusion into the epithelial cell from the lumen, via a co transporter protein

3)Creating a concentration gradient of glucose – higher conc. of glucose in epithelial cell than blood

4)Glucose moves out of cell into blood by facilitated diffusion through a protein channel

Question 6

Describe the mechanism for absorption of lipids by the cells lining the ileum.

Answer 6

1)Monoglycerides and fatty acids diffuse out of micelles (in lumen) into epithelial cell Because lipid soluble

2)Monoglycerides and triglycerides recombine to triglycerides which aggregate into globules

3)Globules coated with proteins to form chylomicrons

4)Leave via exocytosis and enter lymphatic vessels

5)Return to blood circulation