digestion and absorption (module 3)

Question 1

what is digestion?

Answer 1

large biological molecules are hydrolysed into smaller molecules that can be absorbed cross the cell membrane

Question 2

what enzymes hydrolyse proteins?

Answer 2

peptidase (protease)

Question 3

what are the types of peptidases and what do they do?

Answer 3

• endopeptidase hydrolyse peptides bonds between amino acids to form small polypeptide chains
• exopeptidase hydrolyse peptide bonds on terminal amino acids of the polypeptide molecules formed by endopeptidases
• dipeptidase hydrolyse the bond between amino acids of a dipeptide

Question 4

how does endopeptidase benefit exopeptidase?

Answer 4

provides more ends and increase surface area

Question 5

what enzyme hydrolyses glycosidic bonds in starch/carbohydrates?

Answer 5

amylase

Question 6

where is amylase produced?

Answer 6

pancreas and released into small intestine

Question 7

carbohydrates is hydrolysed twice in what order and what enzymes are used for the final product?

Answer 7

starch -> (amylase) -> maltose -> (maltase) -> alpha glucose

Question 8

where are membrane bound dipeptidases and dissachrides found?

Answer 8

the cell membrane of the epithelial cells which line the ileum

Question 9

what are bile salts and what does it do?

Answer 9

bile salts are produced by the liver and they emulsify lipids by forming small droplets which provide a large surface area for lipase to act on

Question 10

what does lipase breakdown lipids into?

Answer 10

monoglycerides and fatty acids

Question 11

how are micelles formed?

Answer 11

the monoglycerides and fatty acids stick to the bile salts forming micelles

Question 12

how do micelles help lipid digestion?

Answer 12

help monoglycerides and fatty acids to be absorbed through membrane

Question 13

what is co transport?

Answer 13

• two molecules transported together through a carrier protein
• one molecule goes down a concentration gradient
• one molecule goes against the concentration gradient

Question 14

what happens during co transport?

Answer 14

• sodium ions transport out of epithelial cell using active transport and the sodium potassium pump
• at the same time potassium ions actively transport into the epithelial cells
• so now there is less low concentration of sodium ions in epithelial cell
• lumen of ileum contains high concentration of sodium ions so now a concentration gradient
• sodium diffuses into epithelial cell using a protein carrier from the lumen down its concentration gradient
• at the same time glucose is transported into epithelial cell against its concentration gradient (active transport)
• glucose then transport into epithelial cell through facilitated diffusion

Question 15

what are the adaptations of small intestine?

Answer 15

• lots of microvilli so large surface area absorption
• large number of proteins (carrier channel etc)
• large number of mitochondria so can make more ATP
• membrane bound enzymes so maintains concentration gradient for faster absorption

Question 16

how are lipids digested?

Answer 16

• micelles carry fatty acid to lining of ileum
• fatty acids and monoglycerides are then absorbed by diffusion
• reformed into triglycerides
• the Golgi apparatus modifies triglycerides and combine them with proteins to form chylomicrons
• chylomicrons are enclosed in vesicle which moves to cell surface membrane
• released by exocytosis