digestion and absorption

Question 1

what happens to large molecules during digestion

Answer 1

they are too big to be absorbed across cell membranes
digestion breaks them down (hydrolysed) into smaller molecules to be absorbed from the gut to blood

Question 2

how are carbohydrates (starch) digested

Answer 2

polysaccharide

amylase hydrolyses starch to maltose (disaccharide)
- amylase produced in salivary glass releases into mouth
- amylase produced by pancreas released into small intestine

membrane bound maltase hydrolyse maltose to glucose

hydrolysis of glycosidic bond

Question 3

how are carbohydrates digested (disaccharides)

Answer 3

membrane bound disaccharidases eg. maltase, sucrase, lactase hydrolyse disaccharide to their monosaccharides eg. glucose and other

Question 4

how are lipids digested

Answer 4

bile salts produced in the liver emulsify lipid to smaller lipid droplets
- increased surface area to speed action of lipases

lipase made in pancreas released into small intestine

hydrolysed to monoglycerides and fatty acids

breaking ester bond

monoglycerides fatty acids and bile salts stick together to form micelles

Question 5

how are proteins digested

Answer 5

endopeptidase
- hydrolyse peptide bond within protein between amino acids in central region
- breaking protein into two or more smaller peptides

exopeptidase
- hydrolyse peptide binds at the ends of proteins
- removing a single amino acid

dipeptidases (type of exopeptidase)
- often membrane bound in ileum
- hydrolyse peptide bond between dipeptide

Question 6

what is the mechanism of absorption of amino acids and monosaccharides

Answer 6

co transport

1. sodium ions actively transported out of epithelial cells lining ileum into blood by sodium potassium pump creating conc. gradient of sodium
2. sodium ions and glucose move by facilitated diffusion into epithelial cell from lumen via co transport protein
   3 creating conc. gradient of glucose
3. glucose moves out of cell into blood by facilitated diffusion through protein channel

Question 7

what is the mechanism of absorption if micelles

Answer 7

1. monoglycerides and fatty acids diffuse out of micelles into epithelial cell because lipid soluble
2. monoglycerides and triglycerides recombine to triglyceride’s which aggregate into globules
3. globules coated with proteins to form chylomicrons
4. leave via exocytosis and enter lymphatic vessels
5. return to blood circulation

Question 8

why does lipase cause a change in pH in the digestion of milk

Answer 8

production of fatty acids
which cause a fall in pH