6.9 Enzymes and digestion

Question 1

What is the human digestive system made up of

Answer 1

A long muscular tube and its associated glands. The glands produce enzymes that hydrolyse large molecules into small ones ready for absorption

Question 2

What are the major parts of the digestive system

Answer 2

1. Oesophagus
2. Stomach
3. Ileum
4. Large intestine
5. Rectum
6. Salivary glands
7. Pancreas

Question 3

What is the oesophagus and what is its role

Answer 3

Carries food from the mouth to the stomach

Question 4

What is the stomach and what is its role

Answer 4

A muscular sac with an inner layer that produces enzymes

Its role is to store and digest food, especially proteins. It has glands that produce enzymes which digest protein

Question 5

What is the ileum and what is its role

Answer 5

A long muscular tube

Food is further digested in the ileum by enzymes that are produced by its walls and by glands that pour their secretions into it.

Question 6

What happens to the inner walls of the ileum

Answer 6

They become folded into villi, giving them a large surface area.

Question 7

What increases the surface area of the ileum more

Answer 7

Tiny projections called microvilli.

Question 8

What do the adaptations to the ileum achieve

Answer 8

An efficient system for absosbing the products of digestion into the blood stream

Question 9

What is the large intestine and what is its role

Answer 9

The large intestine is a tube that absorbs water.

The water is from digestive glands

Question 10

What is the rectum and what is its role

Answer 10

It is the final section of the intestines.

Faeces are stored here before being removed via the anus during egestion

Question 11

What are the salivary glands and what are their role

Answer 11

Glands situated near the mouth.

They pass their secretions via a duct into the mouth. These contain amylase which hydrolyse starch into maltose

Question 12

What is the pancreas and what is its role

Answer 12

A large gland situated below the stomach. It produces a secretion called pancreatic juice.

The pancreatic juice contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch

Question 13

What enzymes does the pancreas produce

Answer 13

Proteases (proteins to amino acids)

Lipases (fats to glycerol and fatty acids)

Amylase (starch to maltose)

Question 14

What are the two stages of digestion

Answer 14

1. Physical breakdown

2. Chemical breakdown

Question 15

What is physical breakdown during digestion

Answer 15

If the food is large, it is broken down into smaller pieces by means of the teeth.

This ensures a large surface area for chemical digestion.

Food is also churned by the muscles in the stomach wall which also physically breaks it down

Question 16

What is chemical digestion

Answer 16

Chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones.

Question 17

How does chemical digestion occur

Answer 17

By enzymes, which function by hydrolysis (adding water over a chemical bond)

Question 18

How do enzymes work in the digestive system

Answer 18

Usually one hydrolyses a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes

Question 19

What are the three digestive enzymes

Answer 19

1. Carbohydrases - Hydrolyse carbohydrates into monosaccharides
2. Lipases - hydrolyse lipids into glycerol and fatty acids
3. Proteases - hydrolyse proteins, ultimately to amino acids

Question 20

What is the principle behind chemical digestion and large molecules

Answer 20

It usually takes more than one enzyme to completely hydrolyse a large molecule

Typically one enzyme hydrolyses the molecule into smaller sections and then other enzymes hydrolyse these sections further into monomers. These enzymes are usually produced in different parts of the digestive system

It is therefore important enzymes are added in the right order

Question 21

Describe the process of starch digestion

Answer 21

1. Saliva enters the mouth via salivary glands and is thoroughly mixed with the food during chewing
2. Saliva contains salivary amylase. This hydrolyses starch into maltose. It also contains mineral salts that maintain pH around neutral - the optimum pH
3. The food is swallowed and enters the acidic stomach where any enzymes are denatured, preventing further hydrolysis
4. The food is passed into the small intestine, where it mixes with the pancreatic juice
5. Pancreatic juice contains pancreatic amylase. This continues the hydrolysis of starch to maltose. Alkaline salts are produced by the pancreas AND intestinal wall to maintain pH around neutral
6. Muscles in the intestine wall push food along the ileum. Its epithelial lining produces maltase. Maltase is not released but is instead part of the cell membrane of epithelial cells - it is a membrane-bound disacchardidase. The maltase hydrolyses maltose from
   starch breakdown into alpha glucose

Question 22

What is maltase

Answer 22

A membrane bound disacchardidase

Question 23

What are two other common disaccharides in a persons diet

Answer 23

Sucrose

Lactose

Question 24

How is sucrose digested

Answer 24

By membrane-bound sucrase which hydrolyses the single glycosidic bond in sucrose. This produces fructose and glucose

Question 25

How is lactose digested

Answer 25

By membrane-bound lactase which hydrolyses the single glycosidic bond in the lactose molecule. This produces glucose and galactose

Question 26

What are digested by lipids

Answer 26

Lipases

Question 27

What are lipases, where are they found and how do they work

Answer 27

enzymes produced by the pancreas that hydrolyse the ester bond found in triglycerides to form fatty acids and monoglycerides.

Question 28

What is a monoglyceride

Answer 28

A glycerol molecule with a single fatty acid molecule attached

Question 29

Describe the process of lipid digestion

Answer 29

Lipids are firstly split up into tiny droplets called micelles by bile salts, which are produced by the liver. This process is called emulsification and increases the surface area of the lipids so that the action of lipases is sped up

Question 30

How are proteins digested

Answer 30

By proteases

Question 31

What are the different proteases

Answer 31

Endopeptidase
Exopeptidase
Dipeptidase

Question 32

What do endopeptidases do

Answer 32

Hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules

Question 33

What do exopeptidases do

Answer 33

Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they release dipeptides and single amino acids

Question 34

What do dipeptidases do

Answer 34

Hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of epithelial cells lining the ileum