Digestion

Question 1

role of protease enzyme

Answer 1

hydrolyse proteins to amino acids

Question 2

role of lipase enzyme

Answer 2

hydrolyse lipids into glycerol and fatty acids

Question 3

role of carbohydrase enzyme

Answer 3

hydrolyse carbohydrates to monosaccharides

Question 4

describe the digestion of starch

Answer 4

• starts in mouth: mastication (chewing), salivary amylase hydrolyses starch to maltose
• in stomach, HCl denatures amylase
• in small intestine: pancreatic amylase continues starch hydrolysis, peristalsis occurs (contraction + relaxation of SI), maltase (membrane-bound enzyme) hydrolyses maltose to glucose

Question 5

why do soluble disaccharides require hydrolysis

Answer 5

they are too big

Question 6

name the disaccharides and what membrane-bound enzymes hydrolyse them

Answer 6

• maltose - maltase
• sucrose - sucrase
• lactose - lactase

Question 7

define digestion

Answer 7

process in which large (insoluble) molecules are hydrolysed by enzymes into small (soluble) molecules, which can be absorbed and assimilated

Question 8

role of exopeptidase in digestion of proteins

Answer 8

hydrolyse peptide bond of terminal amino acids (ones at the end of the chain)

Question 9

role of endopeptidase in digestion of proteins

Answer 9

hydrolyse peptide bond of internal amino acids in polypeptide chain

Question 10

role of dipeptidase in digestion of proteins

Answer 10

hydrolyse peptide bond of single pair of amino acids

Question 11

benefit of endopeptidase enzyme

Answer 11

produces multiple shorter polypeptide chains, which allows more exopeptidases to hydrolyse more terminal peptide bonds, releasing amino acids faster

Question 12

describe the mechanism for the absorption of the products of digestion by cells lining the ileum in mammals

Answer 12

• sodium ions are actively pumped out of the cuboidal cells by active, ATP driven Na/K exchange pumps
• sets up a sodium ion concentration gradient with higher concentration of sodium ions on the outside
• co-transporter facilitates the sodium ions to diffuse in down their gradients to ‘pull in’ glucose molecules into the cytoplasm against its gradient (allow for maximum absorption)
• glucose can passively diffuse out through other carrier proteins onto the other side (passing into blood capillaries)

Question 13

describe the emulsification of lipids

Answer 13

bile salts secreted from liver (act as a detergent) break up globules of triglyceride forming an emulsion. this provides a large surface area for the pancreatic lipase enzyme to hydrolyse the triglycerides into two fatty acids and a monoglyceride (called a micelle)

Question 14

describe how a micelle enters the smooth endoplasmic reticulum

Answer 14

• micelles are lipid soluble, they diffuse across the cell surface membrane of the cells lining the ileum into the intestinal epithelial cells (carry the fatty acids and monoglycerides)
• form vesicles that merge with the SER

Question 15

describe what happens to lipids in the SER

Answer 15

micelles formed back into triglyceride molecules
- form chylomicrons ( vesicles of triglycerides surrounded by a phospholipid membrane- contain lipid proteins which determines their role)
- chylomicrons released by exocytosis into the lacteal (can pass into the lymphatic vessels)

Question 16

where does digestion of lipids occur

Answer 16

the duodenum