pack 5 digestion

Question 1

what is digestion

Answer 1

• is the process by which large molecules in the food we eat are hydrolysed into smaller more soluble molecules that can be absorbed by the body
  two ways
• chemical and physical breakdown

Question 2

starch digestion

Answer 2

in the mouth
- salivary glands secrete saliva which contains enzyme amylase
- this catalyses the hydrolysis of starch into maltose
- glycosidic bonds are broken
(stops in stomach)

in small intestine
- starch digestions continues in the duodenum
- pancreatic amylase is secreted from pancreas
- this catalysts the hydrolysis of any undigested starch molecules into maltose

Question 3

maltose digestion

Answer 3

• maltose is a disaccharide (too large to be absorbed)
• digestion completed by maltase
• membrane bound enzyme lining the small intestine
  -maltase catalysts the hydrolysis of maltose into glucose

Question 4

protein digestion

Answer 4

• hydrolysed by a group of enzymes called peptidases
• begins in the stomach
• endopeptidases
• hydrolyse peptide bonds between amino acids in the central region of the protein molecules forming smaller peptide molecules.
• these protease enzymes are produced by the stomach or pancreas

exopeptidases
- hydrolyses peptide bonds between the terminal amino acids of the protein molecules to release dipeptides or single amino acids

dipeptidases
- hydrolyses peptide bonds holding amino acids of a dipeptide.
- membrane bound enzymes found on the cell surface membrane of the small intestine epithelial cells

Question 5

digestion of lipids

Answer 5

• begins in the duodenum and is completed in the ileum.
• both chemical (enzymes) and physical (emulsification)
• lipids form large droplets when mixed with water.
• bile salts, which are produced by the liver, can break these large droplets up and form smaller droplets.
• this process is called emulsification and increase the surface area of the lipids in order to speed up the action of lipases
• lipids are hydrolysed by enzymes called lipases. lipases are enzymes produced in the pancreas that hydrolyse ester bonds to form fatty acids and glycerol and monoglycerides

Question 6

how are small intestine adapted for absorption

Answer 6

• very long, folded tubes
• lining is folded
• folds have many villi
• villus has single layer of epithelial cells which contain microvilli

Question 7

co- transport

Answer 7

• amino acids and glucose absorption is coupled with the absorption of another substance sodium ions
• sodium ions actively transported from ileum cell to blood
• maintains diffusion gradient for sodium to enter cells from gut
• sodium ions enter by facilitated diffusion with glucose
• glucose leaves the cell and enters the blood by facilitated diffusion

Question 8

absorption of lipids

Answer 8

• the bile salts that are used for emulsification stay associated with these molecules and they all come together to form tiny droplets called micelles
• micelles are soluble in water and transport their content to the epithelial cells of the small intestine.
• when the micelles come into contract with epithelial cells they break down and release the glycerol fatty acids and monoglycerides
• as they are non polar diffusion easily across the cell surface membrane by simple diffusion

Question 9

lipids once inside the cells

Answer 9

• the triglyceride molecules reform (forming chylomicrons) and are transported out of the cell by exocytosis.
• they are first absorbed into vessels called lacteals, but ultimately are transported into the blood