1: BIOLOGICAL MOLECULES - DIGESTION AND ABSORPTION

Question 1

Why does digestion happen?

Answer 1

digestion means that molecules can be easily absorbed from the gut into the blood to be transported around the body to be used by cells

Question 2

What enzyme catalyses the breakdown of starch?

Answer 2

amylase

Question 3

What are the sites of amylase production/use?

Answer 3

• salivary glands
• pancreas

Question 4

What is the product of the digestion of starch?

Answer 4

maltose

Question 5

What enzymes catalyse the breakdown of disaccharides?

Answer 5

disaccharidases

Question 6

What are the sites of production/use of disaccharidases?

Answer 6

membrane bound in the ileum

Question 7

What disaccharidase catalyses the breakdown of maltose?

Answer 7

maltase

Question 8

What disaccharidase catalyses the breakdown of sucrose?

Answer 8

sucrase

Question 9

What disaccharidase catalyses the breakdown of lactose?

Answer 9

lactase

Question 10

What are the products of the digestion of maltose?

Answer 10

2 alpha glucose molecules

Question 11

What are the products of the digestion of sucrose?

Answer 11

glucose + fructose

Question 12

What are the products of the digestion of lactose?

Answer 12

glucose + galactose

Question 13

What type of bond is hydrolysed in the digestion of polysaccharides/disaccharides?

Answer 13

glycosidic bonds

Question 14

What enzymes catalyse the breakdown of polypeptides?

Answer 14

• exopeptidases
• endopeptidases

Question 15

What bonds do endopeptidases break?

Answer 15

peptide bonds within the polypeptide chain

Question 16

What bonds do exopeptidases break?

Answer 16

peptide bonds at the end of the polypeptide chain

Question 17

What are the products of polypeptide digestion with endopeptidase?

Answer 17

2 shorter polypeptide chains

Question 18

What are the products of polypeptide digestion with exopeptidase?

Answer 18

shorter polypeptide chain + 1 amino acid

Question 19

What is the site of production/use of exopeptidases and endopeptidases?

Answer 19

the stomach

Question 20

What enzymes catalyse the breakdown of dipeptides?

Answer 20

dipeptidases

Question 21

What are the products of dipeptide digestion?

Answer 21

2 amino acids

Question 22

What is the site of dipeptidase production/use?

Answer 22

membrane bound in the small intestine

Question 23

What type of bonds are hydrolysed in the digestion of polypeptides and dipeptides?

Answer 23

peptide bonds

Question 24

What enzyme catalyses the breakdown of lipids?

Answer 24

lipase

Question 25

What is the site of lipase production/use?

Answer 25

the pancreas

Question 26

What are the products of lipid digestion?

Answer 26

monoglycerides + 2 fatty acids

Question 27

What type of bond is hydrolysed in the digestion of lipids?

Answer 27

ester bonds

Question 28

What is the function of bile salts?

Answer 28

bile salts emulsify lipids (cause the lipids to form small droplets)

Question 29

What organ produces bile salts?

Answer 29

the liver

Question 30

What is the benefit of emulsifying lipids?

Answer 30

- several small lipid droplets have a larger surface area than a single large droplet (for the same volume of lipid) - this means that the surface area available for lipase to work on increases

Question 31

What happens after the lipids are broken down by lipase?

Answer 31

monoglycerides and fatty acids stick with the bile salts to from micelles

Question 32

What is the function of micelles?

Answer 32

help products of lipid digestion to be absorbed

Question 33

How are lipids absorbed?

Answer 33

- micelles move monoglycerides and fatty acids towards the epithelium - because micelles constantly break up and reform they release monoglycerides and fatty acids - monoglycerides and fatty acids are lipid soluble so they diffuse directly across the epithelial cell membrane - monoglycerides and fatty acids form triglycerides (produced by SER) - golgi body packages triglycerides into chylomicrons - chylomicrons move from the epithelial cell into the lacteal by exocytosis

Question 34

How are glucose and galactose absorbed?

Answer 34

glucose and galactose are absorbed across the ileum epithelium into the bloodstream by active transport via co-transporter proteins

Question 35

How is fructose absorbed?

Answer 35

fructose is absorbed by facilitated diffusion

Question 36

Describe the co-transport of glucose across the ileum epithelium (6 marks)

Answer 36

- Na^+ ions pumped out of epithelial cell by active transport/sodium-potassium pump into blood - maintaining Na^+ ion conc gradient between lumen of ileum and epithelial cell - glucose moves in with Na^+ ion into epithelial cell via co-transporter protein - Na^+ ion moves down conc gradient whilst glucose moves against conc gradient - glucose moves into blood by facilitated diffusion via carrier protein

Question 37

How are amino acids absorbed?

Answer 37

- amino acids are absorbed via co-transport - Na^+ ions are actively transported out of the ileum epithelial cells into the blood which creates an Na^+ ion conc gradient - Na^+ ions can then diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them