3.3.3 Digestion and absorption

Question 1

What is digestion?

Answer 1

Hydrolysis of large insoluble molecules into smaller soluble ones.

Question 2

Which organ produces amylase?

Answer 2

Pancreas

Question 3

Where is maltase produced?

Answer 3

Cells lining the ileum (small intestine)

Question 4

Describe the roles of enzymes of the digestive system in the complete breakdown of starch? (6)

Answer 4

• Amylase
• hydrolyses
• glycosidic bond
• starch to maltose
• maltase
• hydrolyses maltose to glucose

Question 5

Explain how digestion of starch in the gut leads to an increase in glucose concentration in the blood (co transport details not needed)

Answer 5

• hydrolysed by amylase and maltase
• produces glucose in the gut
• monosaccharide small enough to cross the gut wall into the blood

Question 6

Describe the processes involved in the absorption of products of starch digestion (7)

Answer 6

• sodium removed from epithelial cells by active transport through sodium potassium pump
• into blood
• maintaining low concentration on sodium ions in the ileum lining cells
• glucose moves in with sodium ions
• via facilitated diffusion through a co- transporter protein
• glucose moves into blood
• by facilitated diffusion

Question 7

Why is the rise of glucose concentration in the blood slower after consuming the carbohydrate starch instead of sucrose?

Answer 7

• Starch digested to maltose by amylase
• maltose digested to glucose by maltase
• digestion of sucrose is a single step (with only one enzyme)

Question 8

What do endopeptides do?

Answer 8

Hydrolyse the peptide bonds between the amino acids in the centre of the polypeptide (increases the surface area for exopeptidases)

Question 9

What do exopeptidases do?

Answer 9

Hydrolyse the peptide bonds at the end of polypeptide chains that are formed by endopeptidases (terminal amino acid)

Question 10

After endopeptidases and exopeptidases, what is produced? What hydrolyses the peptide bond between the two amino acids in the dipeptides?

Answer 10

Dipeptides and single amino acids
Membrane bound dipeptidases

Question 11

Describe and explain the digestion and absorption of triglycerides

Answer 11

• triglycerides are emulsified by bile salts into small lipid droplets
• to increase surface area for lipase enzyme - faster rate of hydrolysis
• lipase hydrolyses ester bonds in triglycerides into monoglycerides and fatty acids
• micelles contain fatty acids, monoglycerides and bile salts
• Micelles carry monoglycerides and fatty acids to cell surface membrane where they diffuse (non polar) into intestinal epithelial cells
• monoglycerides and fatty acids transported to smooth ER where they’re reformed into triglycerides
• vesicles transport triglycerides to Golgi apparatus which modifies and processes them:
• triglycerides associate with cholesterol and lipoproteins to form chylomicrons
• chylomicrons packaged into golgi vesicles for exocytosis
• chylomicrons then absorbed into lacteals (lymph vessels) in villi

Question 12

What is the role of micelles in the absorption of lipids?

Answer 12

• micelles include bile salts and fatty acids
• make fatty acids more soluble in water
• bring fatty acids to the cells lining the ileum
• maintain higher concentration of fatty acids to lining
• fatty acids absorbed by diffusion

Question 13

Role of bile

Answer 13

• emulsifies lipid droplets into smaller lipid droplets which have a larger SA:V
• for faster hydrolysis into glycerol and fatty acids
• by lipase

Question 14

What are the roles of bile?

Answer 14

• emulsify large lipid droplets into smaller droplets
• which have a larger surface area so can be more easily and quickly hydrolysed by lipase
• form micelles