Enzymes and digestion

Question 2

How is the ileum adapted to carry out efficient exchange of materials?

Answer 2

• presence of villi and micro-villi -> increases the surface area and therefore the rate of absorption
• Have thin walls lined with epithelial cells, which are close to a large network of capillaries

Question 3

How are the villi adapted for efficient absorption?

Answer 3

• Increase surface area for diffusion
• Thin walled, so reduce diffusion pathway
• Contain muscle and can move, mixing the contents of the ileum and therefore maintaining diffusion gradients
• Good blood supply, so the concentration gradient needed for diffusion is maintained
• Micro-villi, which line epithelial cells and increase surface area

Question 4

How are amino acids and monosaccharides absorbed?

Answer 4

Through channel proteins by co-transport and facilitated diffusion

Question 5

What does endopeptidase do?

Answer 5

Hydrolyse the middle bond in a polypeptide chain

Question 6

How are epithelial cells adapted for the efficient absorption of glucose?

Answer 6

• many mitochondria; produce ATP
• channel proteins; needed to carry ions/larger molecules across the cell-surface membrane
• membrane-bound enzymes; digest disaccharides
• Have lots of co-transport proteins
• have large SA to volume ratio

Question 7

What is a physical method involved in digestion?

Answer 7

chewing/mastication; breaks large pieces into small (teeth and stomach)

Question 8

Why are larger pieces broken into smaller pieces in digestion?

Answer 8

• increases SA for enzymes
• easier to swallow

Question 9

What enzyme breaks down CHOs

Answer 9

amylase

Question 10

Where is amylase produced?

Answer 10

• salivary glands (mouth)
• Pancreas

Question 11

Why is the presence of mineral salts important in the mouth?

Answer 11

maintain the pH at 7 to stop enzymes from denaturing

Question 12

What does amylase hydrolyse starch into?

Answer 12

maltose

Question 13

What happens to amylase in the stomach?

Answer 13

it is denatured

Question 14

Why are the alkaline salts produced by the pancreas important in the digestion of CHOs?

Answer 14

Maintain pH at 7

Question 15

Where is maltase/disaccharidase found?

Answer 15

Ileum (it is membrane bound)

Question 16

What do enzymes do?

Answer 16

Enzymes hydrolyse large insoluble molecules into smaller soluble molecules

Question 17

What enzyme breaks down lipids?

Answer 17

lipase

Question 18

What does lipase hydrolyse lipids into?

Answer 18

monoglyceride and fatty acids

Question 19

What is the purpose of emulsification?

Answer 19

• increase SA for enzyme action

Question 20

What are lipids emulsified into? What by?

Answer 20

From lipids into micelles, by bile salts

Question 21

What makes up a micelle?

Answer 21

bile salts, a monoglyceride and fatty acids

Question 22

What enzymes break down proteins?

Answer 22

peptidases

Question 23

What are the products formed after a polypeptide is broken down by exopeptidase?

Answer 23

amino acids, dipeptides

Question 24

Which type of peptidase is membrane-bound?

Answer 24

dipeptidase

Question 25

How are amino acids and monosaccharides absorbed?

Answer 25

diffusion and co-transport

Question 26

Describe how a triglyceride is absorbed

Answer 26

• micelle containing bile salts, monoglyceride and fatty acids
• micelle breaks as it comes into contact with epithelial cells lining the ileum
• monoglyceride and fatty acids are non-polar and so they can diffuse across cell-membranes into the cell.
• when in the cell they move to the SER
• in the SER, they are reformed into triglycerides
• they then move to the golgi, where they associate with lipoprotein and cholesterol to form a chylomicron
• this leaves the cell by exocytosis and enter a lacteal
• the chylomicrons enter the blood, the triglycerides are hydrolysed (by an enzyme on endothelial cells) and then the monoglyceride and fatty acids diffuse into cells

Question 27

Suggest why both exopeptidases and endopeptidases are used as opposed to just using exopeptidases

Answer 27

• Endopeptidases hydrolyse internal bonds, whereas exopeptidases hydrolyse bonds at the end of protein molecules.
• endopeptidase activity increase the surface area for the exopeptidases to work on.

Question 28

What is the role of micelles?

Answer 28

• carry fatty acids and bile salts
• move to ileum
• make more soluble
• maintain concentration gradient
• fatty acids absorbed by diffusion