6.9 enzymes and digestion

Question 1

Glands in our body release enzymes
What do these do

Answer 1

They hydrolyse large molecules into small ones ready for absorption

Question 2

What does the oesophagus do in digestion

Answer 2

It is the tube that carries food from the mouth to the stomach

Question 3

What are the major parts of digestive system in order

Answer 3

Mouth (salivary glands)
Oesophagus
Stomach
Pancreas
Small intestine
Large intestine
Rectum

Question 4

What does the stomach do in digestion

Answer 4

. It is a muscular sac with an inner layer that produces enzymes
. The muscles can churn the food in physical breakdown
. Its role is to store and digest food, especially proteins
. It has glands to produce enzymes eg pepsin

Question 5

What does the ileum do in digestion

What adaptations does it have

Answer 5

. Long muscular tube in the small intestine
. Enzymes are in it that are produced by the walls and by glands that pour their secretions into it, to digest food

. Inner walls of it are folded into villi which give it a large surface area, with millions of microvilli on the epithelial cells of each villus
. This adapts the ileum for absorbing the products of digestion into the bloodstream

Question 6

What does the large intestine do in digestion

Answer 6

It absorbs water, and most of the water that is absorbed is water from secretions of many digestive glands

Question 7

What does the rectum do in digestion

Answer 7

It is in the final section of the intestines.

Faeces is stored here before being removed via anus by egestion

Question 7

What two things do the salivary glands do in digestion

Answer 7

Situated near the mouth, where they pass their secretions via a duct in the mouth
. These secretions contain the enzyme amylase to hydrolyse starch into maltose

Also, they contain mineral salts to help maintain the PH to neutral which is the optimum PH for enzymes to work

Question 8

What does the pancreas do in digestion

Answer 8

. It is a large gland below the stomach that secretes pancreatic juices
. These juices contain many proteins eg
Proteases to hydrolyse proteins
Lipase to hydrolyse lipids
Amylase to hydrolyse statch

Question 9

What are the two stages of digestion in humans

Answer 9

. Physical breakdown
. Chemical digestion

Question 10

Describe the physical breakdown of food

Answer 10

If food is large it is broken down into smaller pieces by structures eg the teeth
This makes it possible to ingest food, and also provides a large surface area for chemical digestion
. Food is also churned by muscles in the stomach wall which physically breaks it up

Question 11

What are the 3 types of enzyme in digestion

Answer 11

. Carbohydrases: Hydrolyse carbohydrates into monosaccharides eventually

. Lipases: Hydrolyse lipids into glycerol and fatty acids

. Proteases: Hydrolyse protein into amino acids

Question 11

What occurs in chemical digestion

How do all enzymes function

Answer 11

Chemical digestion hydrolyses large, insoluble molecules into small soluble ones
It is carried out by enzymes

ALL enzymes do hydrolysis to split up large molecules into smaller ones by adding water to break the chemical bonds that hold them together

Question 12

What is the first stage of carbohydrates getting broken down with amylase
What is the second enzyme after this and where is it found

Where does it occur

Where else is this enzyme found

Answer 12

In the mouth, the enzyme amylase is present and it hydrolyses the glycosidic bonds in starch molecules to produce the disaccharide maltose

Then maltose is hydrolysed into alpha glucose by maltase which is produced in the lining of the ilium

Pancreas also produces amylase

Question 13

Describe process of digestion of carbohydrates

Answer 13

. Saliva enters mouth from salivary glands and is thoroughly mixed with food whilst chewing

. Saliva contains the enzyme amylase which hydrolyses starch to maltose. It also contains mineral salts to keep PH neutral in the mouth for the amylase

. The food is swallowed and enters the stomach where it is acidic, and the acid denatures amylase and prevents further hydrolysis of starch

. Then, food goes to small intestine where it mixes with pancreatic juices that contain amylase
So this amylase continues the hydrolysis of starch to maltose
The PH is neutral again for amylase in the small intestine due to alkaline salts produced by pancreas and intestine wall

. Muscles in intestine wall push the food to the ilium which produces the maltase enzyme to break down maltose into glucose

. It is released by epithelium cells in the lining but never enters the lumen of the ilium so is a membrane bound disaccharidase

Question 14

Describe the maltase enzyme and how it breaks down the maltose

Answer 14

It is in the epithelium cells in the lining of the ileum and stays in the lining
So is membrane bound
It hydrolyses the disaccharide maltose into two constituent glucose by breaking the glycosidic bond

Question 15

There are two other disaccharides in the diet that are hydrolysed
Sucrose and fructose

How are these hydrolysed

Answer 15

. Sucrase hydrolyses sucrose to make fructose and glucose monosaccharides
It hydrolyses the glycosidic bond in sucrose
. It is also a membrane bound enzyme

. Lactase hydrolyses lactose to glucose and galactose by breaking the glycosidic bond
It is membrane bound also

Question 16

Describe the role of lipids in digestion
What is the enzyme

Where does this digestion occur

Answer 16

Lipases hydrolyse lipids by hydrolysing the ester bond in triglycerides to form fatty acids and glycerol

Lipases are produced in the pancreas, so is a pancreatic juice which then

It occurs in the small intestine, before the ileum

Question 17

What is bile, where is it made from

Answer 17

. Bile is made in liver but is stored in gall bladder
. It is released into the small intestine where it….

Emulsifies lipids by breaking them down into smaller molecules
And neutralises the stomach acid whilst entering the small intestine which needs a neutral PH for enzymes to work

Question 18

How do lipases digest lipids

Answer 18

. Lipids are split up into droplets called micelles by bile
. This is emulsification which increases surface area of lipids so the lipase enzyme can work
. Lipase will hydrolyse the ester bond between a glycerol and fatty acids

Question 19

How are proteins digested

Answer 19

• Proteins are large and complex molecules
• They are hydrolysed by peptidases (proteases) to break them down into amino acids

Question 20

What are the 3 types of proteases

Answer 20

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

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

. Dipeptidases: Hydrolyse the bond between two amino acids in a dipeptide produced by exopeptidase
These are membrane bound enzymes and are part of the cell membrane of epithelial cells lining the ileum