Enzymes and Digestion

Question 1

How is the ileum adapted to carry out efficient gas exchange?

Answer 1

• 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 2

How are the villi adapted for efficient absorption?

Answer 2

• 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 3

How are amino acids and monosaccharides absorbed?

Answer 3

Through channel proteins by co-transport and facilitated diffusion

Question 4

What does endopeptidase do?

Answer 4

Hydrolyse the middle bond in a polypeptide chain

Question 5

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

Answer 5

• 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 6

What is a physical method involved in digestion?

Answer 6

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

Question 7

Why are larger pieces broken into smaller pieces in digestion?

Answer 7

• increases SA for enzymes
• easier to swallow

Question 8

What enzyme breaks down CHOs

Answer 8

amylase

Question 9

Where is amylase produced?

Answer 9

• salivary glands (mouth)
• Pancreas

Question 10

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

Answer 10

maintain the pH at 7 to stop enzymes from denaturing

Question 11

What does amylase hydrolyse starch into?

Answer 11

maltose

Question 12

What happens to amylase in the stomach?

Answer 12

it is denatured

Question 13

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

Answer 13

Maintain pH at 7

Question 14

Where is maltase/disaccharidase found?

Answer 14

Ileum (it is membrane bound)

Question 15

What do enzymes do?

Answer 15

Enzymes hydrolyse large insoluble molecules into smaller soluble molecules

Question 16

What enzyme breaks down lipids?

Answer 16

lipase

Question 17

What does lipase hydrolyse lipids into?

Answer 17

monoglyceride and fatty acids

Question 18

What is the purpose of emulsification?

Answer 18

• increase SA for enzyme action

Question 19

What are lipids emulsified into? What by?

Answer 19

From lipids into micelles, by bile salts

Question 20

What makes up a micelle?

Answer 20

bile salts, a monoglyceride and fatty acids

Question 21

What enzymes break down proteins?

Answer 21

peptidases

Question 22

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

Answer 22

amino acids, dipeptides

Question 23

Which type of peptidase is membrane-bound?

Answer 23

dipeptidase

Question 24

How are amino acids and monosaccharides absorbed?

Answer 24

diffusion and co-transport

Question 25

Describe how a triglyceride is absorbed

Answer 25

• 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 26

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

Answer 26

• 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 27

What is the role of micelles?

Answer 27

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

Question 28

Explain the advantage of lipid droplet and micelle formation

Answer 28

• droplets increase surface area
• so faster hydrolysis
• micelles transport monoglycerides and fatty acids to epithelial cells

Question 29

Explain the advantage of lipid droplet and micelle formation

Answer 29

• droplets increase surface area
• so faster hydrolysis
• micelles transport monoglycerides and fatty acids to epithelial cells