3.3 Digestion and absorption

Question 1

What is the digestion

Answer 1

The hydrolysis of large biological molecules into smaller molecules which can be absorbed across cell membranes.

Question 2

What type of enzymes are digestive enzymes

Answer 2

Extracellular, meaning they work outside of cells.

Question 3

What are the 3 main types of digestive enzymes

Answer 3

• Carbohydrases
• Proteases
• Lipases

Question 4

What are the 5 main stages of digestion

Answer 4

1. Ingestion
2. Physical digestion
3. Chemical digestion
4. Absorption
5. Assimilation

Question 5

Where does the digestion of carbohydrates take place

Answer 5

The mouth and small intestine.

Question 6

How are carbohydrates digested (+ enzymes involved).

Answer 6

• Amylase (type of carbohydrase) hydrolyses starch into maltose.
• Maltase hydrolyses maltose into glucose.
• Glucose can then be absorbed into the epithelial cells of the small intestine which can then pass into the bloodstream.

Question 7

What are 3 types of protease enzyme

Answer 7

• Endopeptidases
• Exopeptidases
• Dipeptidases

Question 8

What is the role of endopeptidases in digestion

Answer 8

They hydrolyse peptide bonds within polypeptide chains to produce dipeptides.

Question 9

What is the role of exopeptidases in digestion

Answer 9

They hydrolyse peptide bonds at the ends of polypeptide chains to produce dipeptides.

Question 10

What is the role of dipeptidase in digestion

Answer 10

They hydrolyse dipeptides into amino acids.

Question 11

Describe the process of digesting proteins

Answer 11

• Begins in the stomach. Endopeptidases hydrolyse peptide bonds into smaller polypeptide chains.
• This enzyme is secreted along with HCl, causing the stomach pH to be low.
• The partially digested food moves to the small intestine.
• Fluid secreated by the pancreas travels to the small intestine and helps neutralise the acid mixture. The pancreatic juice contains endopeptidases and exopeptidases.
• The smaller polypeptide chains are broken down into dipeptides.
• Dipeptidase (found within the cell surface membrane) hydrolyes the dipeptides into amino acids whuch are released into the cytoplasm of the cell.

Question 12

Where does the digestion of lipids take place

Answer 12

In the small intestine.

Question 13

Describe the process of digesting lipids

Answer 13

• Bile salts (produced by liver, secreted by gall bladder) split the lipids into tiny droplets called micelles.
• Micelles brush against the villi of the ileum, further emulsifying them (increases SA for lipases).
• Lipases hydrolyse them into monoglycerides and fatty acids which can diffuse freely through the membrane (as non-polar) into epithelial cells.
• Transported to the SER where they are reformed into lipids (e.g. triglycerides).
• They are then transported to the golgi, packaged with cholesterol and other lipoproteins to form chylomicrons.
• Chylomicrons are then removed into the lacteal vessels (part of the lymph system) by exocytosis.

Question 14

What happens to products of digestion

Answer 14

They are absorbed by the cells lining the ileum of mammals.

Question 15

How are amino acids absorbed

Answer 15

• Absorbed by facilitated diffusion through specific carrier molecules in the cell surface membrane of epithelial cells.
• Each amino acids also transports an Na+ ion into the epithelial cells, so process is co transport.
• Na+ is transported by active transport.