TOPIC 3 - digestion and absorption

Question 1

define digestion.

Answer 1

the hydrolysis of large insoluble molecules, into smaller molecules that can be absorbed across cell membranes.

Question 2

which enzymes are involved in carbohydrate digestion? where are they produced?

Answer 2

• amylase in mouth
• maltase , sucrase , lactase in membrane of small intestines

Question 3

what are the substrates and products of carbohydrate digestive enzymes?

Answer 3

amylase - starch into smaller polysaccharides
maltase - maltose into 2x glucose
sucrase - sucrose into glucose and fructose
lactase - lactose into glucose and galactose

Question 4

where are lipids digested?

Answer 4

small intestine

Question 5

what needs to happen before lipids can be digested?

Answer 5

lipids must be emulsifies by bile salts into smaller soluble molecules called micelles= increasing SA

Question 6

where is bile produced?

Answer 6

in the liver

Question 7

how are lipids digested?

Answer 7

lipase hydrolyses the ester bonds between the monoglycerides and the fatty acids.

Question 8

which enzymes are involved in protein digestion? what are their roles?

Answer 8

endopeptidase = break between specific amino acids in the middle of a polypeptide

exopeptidase = break between specific amino acids at the end of a polypeptide.

dipeptidase = break dipeptides into amino acids.

Question 9

how are certain molecules absorbed into the ileum despite a negative concentration gradient?

Answer 9

through co-transport

Question 10

which molecules require co transport?

Answer 10

amino acids and monosaccharides

Question 11

explain how sodium ions are involved in co transport?

Answer 11

Na+ is actively transported out of the cell into lumen, creating a diffusion gradient.
Nutrients are then taken up into the cells along with Na+ ions.

Question 12

why do fatty acids and monoglycerides not require co transport?

Answer 12

these molecules are non polar which means they can easily diffuse across the membrane of epithelial cells.

Question 13

describe the absorption of lipids by a mammal, including the role of a micelle?

Answer 13

• bile salts combine with monoglycerides and fatty acids to form micelles
• micelles make fatty acids more soluble in water
• fatty acids are absorbed by diffusion into the epithelial cell
• Triglycerides are reformed in the epithelial cells
  and clump into globules
• globules form cholymicrons which are packaged into vesicles
• Vesicles fuse with cell membrane releasing chylomicrons by exocytsis
• Chylomicrons enter lymphatic vessels and eventually return to blood circulation