3.3 Digestion + Absorption

Question 1

Define digestion

Answer 1

The hydrolyisis of polymers to monomers for absorption across cell membranes

Question 2

What do all membrane-bound disaccaridases do to disaccharides

Answer 2

Hydrolyse glycosidic bonds within the disaccharide to form the two monosaccharides

Question 3

What does maltase hydrolyse into what

Answer 3

Maltose into two glucose molecules

Question 4

What does lactase hydrolyse into what

Answer 4

Lactose into glucose and galactose

Question 5

What does sucrase hydrolyse into what

Answer 5

Sucrose into glucose and fructose

Question 6

Function of amylase

Answer 6

Hydrolysises glycosidic bonds within starch to form maltose

Question 7

Outline the three stages to absorption of glucose

Answer 7

• Sodium ions activly transported out of ileum epithelial cell into blood
• Glucose co-transported with sodium ions from gut to ileum epithelial cell
• Glucose moves by faccilitated diffusion from ileum epithelial cell to blood

Question 8

Explain the first stage of abosoption of glucose

Answer 8

• Sodium ions actively transported out of ileum capillary cell into blood by sodium-potassium pump
• ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions

Question 9

Explain the second stage of glucose absorption

Answer 9

• Maintains a diffusion gradient for sodium ions to enter the ileum epithelial cell from the gut through carrier proteins by faccilitated diffusion
• Glucose is co-transported with sodium ions
• Glucose moved into ileum epithelial cell through a co-transport protein by facillitated diffusion

Question 10

Explain the third stage of glucose absorption

Answer 10

Glucose moves by faccilitated diffusion from ileum epithelial cell to blood capillary through a carrier protein

Question 11

Explain the function of lipase

Answer 11

Hydrolyses ester bonds within triglycerides to form monoglycerides and fatty acids

Question 12

What are the functions of bile salts

Answer 12

• Emulsify lipids into smaller droplets
• Form micelles

Question 13

Why do bile salts emulsify lipids into smaller droplets

Answer 13

• Increase their surface area
• Faster hydrolysis by lipase

Question 14

Describe and explain how bile salts form micelles, and their function

Answer 14

• Formed of bile salts, monoglycerides and fatty acids
• Micelles allow fatty acids to become more soluble
• Transports monoglycerides and fatty acids to ileum cell wall, to be absorbed into the ileum epithelial cell
• Fatty acids diffuse through the cell membrane

Question 15

Explain the first process of lipid absorption

Answer 15

• Micelles contain bile salts and monoglycerides
• Movement of ileum brings micelles into contact with ileum epithelial cell where it breaks down
• Monoglycerides and fatty acids are absorbed by epithelial cell via simple diffusion

Question 16

Outline the stages of lipid absorption

Answer 16

• Micelles
• Modification
• Chylomicrons

Question 17

Explain the second stage of lipid absorption

Answer 17

• Monoglycerides and fatty acids transported to smooth endoplasmic reticulum, where they are reformed to triglycerides
• Triglycerides transported to SER where associated with cholestrol and proteins to form lipoproteins
• They form chylomicrons

Question 18

Explain the third stage of lipid absorption

Answer 18

• Chylomicrons transported by vesicles to cell-surface membrane
• **Vesicles fuse with cell-surface membrane **and are released by exocytosis
• Chylomicrons enter lacteal

Question 19

Function of endopeptididases

Answer 19

• Hydrolyse internal peptide bonds in the middle of polypeptide chains
• Create more terminal ends and smaller polypeptide chains
• Increase the surface area for exopeptididases to act

Question 19

Function of exopeptididases

Answer 19

Hydrolyse peptide bonds at terminal ends of polypeptide chains

Question 20

Describe the apperance of dipeptidases and where they are produced

Answer 20

• Membrane-bound
• Duodenum wall

Question 21

Outline the three stages to amino-acid absorption

Answer 21

• Sodium ions activly transported out of ileum epithelial cell into blood
• Amino-acids move co-transported
• Amino-acids move into blood

Question 22

Explain the first stage of amino-acid absorption

Answer 22

• Sodium ions activly transported out of ileum epithelal cells into blood by sodium-potasium pump
• ATP hydrolysis changes the carrier proteins shape, to allow movement of sodium ions

Question 23

Explain the second stage of amino acid absorption

Answer 23

• Maintains a diffusion gradient for sodium ions to move into the ileum epithelial cell from the gut by facillitated diffusion
• Amino-acids are co-transported with sodium ions
• Amino-acids move into ileum epithelial cell from the gut through a co-transport protein via facilitated diffusion

Question 24

Explain the final stage in amino-acid absorption

Answer 24

Amino-acids move by faccilitated diffusion from the ileum epithelial cell to the blood capillary by a protein carrier