[Unit 3.3] Digestion and Absorption

Question 1

what do carbohydrase’s do

Answer 1

catalyse hydrolysis of carbohydrates into disaccharides and monosaccharides

Question 2

what do proteases do

Answer 2

catalyse hydrolysis of proteins and peptides into amino acids

Question 3

what do lipases do

Answer 3

catalyse hydrolysis of triglycerides into fatty acids and glycerol

Question 4

how does starch get digested

Answer 4

• mouth: salivary amylase begins breaks down starch into maltose
• Stomach: amylase denatured by HCl in stomach
• Small intestine: pancreatic amylase digest starch to maltose. Maltase attached to epithelium of villi digests maltose into glucose

Question 5

how does intracellular digestion of maltose happen

Answer 5

• epithelial cells on villi synthesize maltase
• maltase embedded into plasma membrane of microvilli
• maltose binds to maltase (in brush border)
• hydrolysed into glucose
• glucose released into lumen or absorbed into epithelial cell.

Question 6

what does sucrose break down into. what enzyme catalyses this reaction

Answer 6

• glucose and fructose
• sucrase

Question 7

what does lactose break down into. what enzyme catalyses this reaction

Answer 7

• glucose and galactose
• lactase

Question 8

what does maltose break down into. what enzyme catalyses this reaction

Answer 8

• glucose and glucose
• maltase

Question 9

How is glucose absorbed into the blood

Answer 9

• Na+ ions leave epithelial cell and enter blood;
• (Transport out is by) active transport / pump / via carrier protein using ATP;
• So, Na+ conc. in cell is lower than in lumen (of gut);
• Sodium/Na+ ions enter by facilitated diffusion;
• Glucose absorbed with Na+ ions against their concentration/diffusion gradient / glucose absorbed down an electrochemical gradient;

Question 10

why are proteases secreted in an inactive form

Answer 10

to prevent self digestion

Question 11

what are endopeptidases

Answer 11

catalyse hydrolysis of peptide bonds between specific amino acids in the middle of the polypeptide chain

Question 12

what are exopeptidases

Answer 12

catalyse hydrolysis of peptide bonds between amino acids at the ends of the chain. producing dipeptides

Question 13

what are dipeptidases

Answer 13

attached to epithelium of villi. hydrolyse peptide bond between two amino acids.

Question 14

how are amino acids absorbed into the blood

Answer 14

• Na+ ions leave epithelial cell and enter blood;
• (Transport out is by) active transport / pump / via carrier protein using ATP;
• So, Na+ conc. in cell is lower than in lumen (of gut);
• Sodium/Na+ ions enter by facilitated diffusion;
• amino acids absorbed with Na+ ions against their concentration/diffusion gradient / amino acids absorbed down an electrochemical gradient;

Question 15

why are optimal pH levels different in Pepsin and Trypsin

Answer 15

Pepsin works in the stomach. (pH 2)
Trypsin works in the duodenum, where the pancreas secretes hydrogen carbonate ions to produce alkaline conditions.

Question 16

where does lipid digestion start

Answer 16

duodenum

Question 17

where does lipid digestion finish

Answer 17

ileum

Question 18

what organ secretes lipase

Answer 18

pancreas

Question 19

how are lipids emulsified

Answer 19

by bile salts

Question 20

why are lipids emulsified

Answer 20

to turn large droplets into smaller droplets
which increases surface area
and makes them soluble in water
as bile salts make them polar

Question 21

how are products of lipid digestion absorbed into the blood

Answer 21

• products bind to bile salts
• forming water soluble micelles
• micelles transport products to epithelial cells
• micelles break and release their contents into epithelial cells for simple diffusion into blood