[6.9] enzymes and digestion

Question 1

where is amylase secreted?

Answer 1

• salivary glands in mouth
• pancreas into the small intestine

Question 2

digestion of starch: maltose

Answer 2

1. amylase hydrolyses starch to produce the disaccharide maltose
2. membrane-bound disaccharidase maltase hydrolyses maltose into two alpha glucose molecules
3. these are small enough to be absorbed

Question 3

digestion of starch: sucrose

Answer 3

1. amylase hydrolyses starch to produce the disaccharide sucrose
2. membrane-bound disaccharidase sucrase hydrolyses sucrose into a molecule of glucose and a molecule of fructose
3. these are small enough to be absorbed

Question 4

digestion of lactose

Answer 4

2. membrane-bound disaccharidase lactase hydrolyses lactose into a molecule of glucose and a molecule of galactose
3. these are small enough to be absorbed

Question 5

where are membrane-bound disaccharidases made and bound?

Answer 5

• made in the epithelial lining of the ileum (small intestine)
• then bound as extrinsic proteins in the ileum epithelial cells

maltase, sucrase, lactase

Question 6

what do lipases hydrolyse, where are they produced and where do they release into?

Answer 6

• hydrolyse lipids
• hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides
• produced in pancreas
• released into small intestine

Question 7

where is bile produced, stored and released into?

Answer 7

• produced in liver
• stored in gall bladder
• released into small intestine

Question 8

describe how lipids are emulsified very briefly (6)

Answer 8

1. droplet of triglyceride
2. bile
3. smaller droplets with bigger surface area
4. lipase
5. monoglyceride + 2 fatty acids
6. micelles

Question 9

what is emulsification?

Answer 9

it describes the process by which the surface area of lipids is increased so that the action of lipases is sped up

Question 10

what are the advantages of micelles?

Answer 10

• droplets increase surface area for lipase so faster digestion of lipids
• micelles carry fatty acids and glycerol to intestinal epithelial cell membrane

Question 11

what is the role of endopeptidases?

Answer 11

• to hydrolyse peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
• adding endopeptidases increases the number of ends for exopeptidases to work on

Question 12

what are some examples of endopeptidases and where are they made?

Answer 12

• pepsin - produced by stomach lining
• trypsin and chymotrypsin - produced by pancreas, secreted into small intestine

Question 13

what is the role of exopeptidases?

Answer 13

• to hydrolyse peptide bonds between terminal amino acids at the end of the peptide molecules formed by endopeptidases
• only these single amino acids are small enough to be absorbed across the small intestine

Question 14

where are dipeptidases made and bound?

Answer 14

• made in the ileum epithelial lining
• bound as extrinsic proteins on cell surface membrane of epithelial cells of small intestine

Question 15

what is a dipeptidase?

Answer 15

• an exopeptidase that hydrolyses the bond between the two amino acids of a dipeptide
• ie. an exopeptidase that digest dipeptides into single peptides to be absorbed

Question 16

describe how proteins are digested in the human gut [4]

Answer 16

1. hydrolysis of peptide bonds
2. endopeptidases break polypeptides into smaller peptide chails
3. exopeptidases remove terminal amino acids
4. dipeptidases hydrolyse dipeptides into amino acids