3.3.3 Digestion And Absorption

Question 1

How is starch digested in mammals

Answer 1

Amylase hydrolyses strach to maltose

This is then hydrolysed by membrane bound maltase to glucose

The glycosidic bond is hydrolysed

Question 2

Digestion of maltose, sucrose, lactose

Answer 2

Maltose (maltase) - glucose and glucose

Sucrose (sucrase) - glucose and fructose

Lactose (lactase) - glucose and galactose

Question 3

How are lipids digested

Answer 3

Bile slats (produced by the liver) emulsify lipids causing them to form smaller lipids

This increases SA so lipase can work faster

Lipase hydrolyses lipids into glycerol and fatty acids

An ester bond is hydrolysed

Question 4

How are proteins digested

Answer 4

Endopeptidase breaks hydrolyses internal (peptide) bonds to form smaller poly peptides

Expertises - hydrolyses terminal (peptide) bonds and the ends Ong a polypeptide to form single amino acids

Membrane bound dipeptides - hydrolyses terminal (peptide) bonds between dipeptides to form 2 amino acids

Question 5

Why are membrane bound enzymes important

Answer 5

Maintain a conc grated for absorption

Question 6

How are monosaccharides (glucose) and amino acids absorbed in mammals

Answer 6

Co transport:
Na+ actively transports from epithelial cells lining ileum to blood.
Creates a conc gradient of Na+

Na+ enters epithelial cells down conc gradients with a monosaccharide or amino acids Membrane bound against its conc gradient. This happens via a co-transporter protein

Monosaccharide or amino acids move down and conc gradient to the blood (via facilitated diffusion)

Question 7

Pathway of absorption

Answer 7

Lumen(inside ileum)-cells lining ileum- blood

Question 8

Absorption of lipids with micelles

Answer 8

Bile salts combine with monoglycerides and fatty acids to form micelles

They make fatty acids and monoglycerides more soluble in water

They carry them to the cells lining the ileum, where they are broken downs an released

This keeps a high concentration of fatty acids and monoglycerides near cells lining the ileum

Once absorbed the form triglycerides and aggregate into globules

Globules are the coated in proteins forming chylomicrons which are packaged into vesicles

They moved to the cell membrane, fusing with it and release the chylomicrons via exocytosis.

Chylomicrons enter the lymphatic vessels and return to the blood