Unit 3- Digestion =)

Question 1

Describe the role of the enzymes of the digestive system in the complete breakdown of starch. (5)

Answer 1

• salivary & pancreatic amylase
• hydrolyse glycosidic bonds
• starch –> maltose
• maltase in small intestine
• maltose –> glucose

Question 2

Explain the advantages of lipid droplet and micelle formation. (3)

Answer 2

• droplet- ↑ s.a. for lipase
• faster hydrolysis of lipids
• micelle- transport fatty acids & monoglycerides to membrane

Question 3

Describe the process involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels. (5)

Answer 3

• micelles contain bile salts + monoglycerides & fatty acids
• make f.a. ↑ soluble in water
• micelles transport f.a. to cell
• maintain ↑ conc. of f.a. to cell
• absorbed by diffusion
• triglyceride reformed (at RER)
• vesicles move to cell mem for exocytosis

Question 4

The action of the sodium- potassium pump is linked to a membrane-bound ATP hydrolase enzyme.
Explain the function of this ATP hydrolase. (2)

Answer 4

• hydrolysis of ATP (ADP+Pi) releases energy
• ✔️ ions to be moved against conc. gradient in a.t.

Question 5

The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Explain how. (2)

Answer 5

• maintains conc. gradient of Na+ from lumen of ileum into cell
• Na+ moves in by co-transport, bringing glucose w/ it

Question 6

Describe the role of enzymes in the digestion of proteins in a mammal. (4)

Answer 6

• hydrolysis of peptide bond
• endopeptidase- middle of polypeptide–> shorter polypeptides + ↑ no. of ends
• exopeptidase- end of protein (remove terminal a.a.)–> dipeptides
• dipeptidase- dipeptides –> single a.a.

Question 7

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions.
Explain how. (3)

Answer 7

• Na+ from ileum cells into blood by a.t.
• maintains diffusion gradient for Na+ to enter cells from lumen
• glucose enters by co-transport w/ Na+ ions

Question 8

Use your knowledge of lipid digestion to explain why concentration of fatty acids increased while that of triglycerides decreased at 75 minutes after meal was taken.
You should assume that no absorption had occurred. (3)

Answer 8

Triglyceride ↓ as:
1. lipase digests triglycerides
2. by hydrolysis
3. breaking the ester bonds between f.a. & glycerol

Question 9

Maltose is hydrolysed by the enzyme maltase.
Explain why maltase catalyses only this reaction. (3)

Answer 9

• tertiary structure- specifically shaped a.s.
• only maltose can fit
• forms enzyme-substrate complex

Question 10

The concentration of glucose in the blood rises after eating a meal containing carbohydrates.
The rise is slower if the carbohydrate is starch rather than sucrose.
Explain why. (3)

Answer 10

• starch digested into maltose
• maltose digested into glucose
• sucrose- single step, only 1 enzyme

Question 11

Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own. (2)

Answer 11

• endo hydrolyse internal peptide bonds
• ↑ s.a. / ends for exo to work on

Question 12

Suggest how the golgi apparatus is involved in the absorption of lipids. (3)

Answer 12

• modifies triglycerides
• combines w/ proteins
• packaged for release

Question 13

Describe and explain 2 features you would expect to find in a cell specialised for absorption. (2)

Answer 13

1. folded mem –> ↑ s.a. for absorption
2. ↑ no. of carrier proteins –> fast rate
3. ↑ no. of mitochondria –> make ↑ ATP for a.t.
4. ↑ mem-bound (digestive) enzymes –> maintains conc gradient ==> faster absorption

Question 14

Describe the action of membrane-bound dipeptidases and explain their importance. (2)

Answer 14

• hydrolyse peptide bonds –> release a.a.
• a.a. can cross cell mem but dipeptides x

Question 15

The action of endopeptidases and exopeptidases can increase the rate of protein digestion.
Descrobe how. (2)

Answer 15

• exo hydrolyse peptide bonds at ends of polypeptide + endo hydrolyse internal peptide bonds within polypeptide
• ↑ ends

Question 16

Describe the complete digestion of starch by a mammal. (4)

Answer 16

1. Hydrolysis;
2. (Of) glycosidic bonds;
3. (Starch) to maltose by amylase;
4. (Maltose) to glucose by disaccharidase/maltase;
5. Membrane-bound (disaccharidase/maltase);

Question 17

What is digestion? (2)

Answer 17

• hydrolysis of
• larger/ insoluble substances into smaller/ soluble substances