6.9 Enzymes and digestion

Question 1

Define enzymes

Answer 1

a protein or RNA that acts as a catalyst and so alters the speed of a biochemical reaction

Question 2

Define digestion

Answer 2

the process in which large molecules are hydrolysed by enzymes into small molecules, which can be absorbed and assimilated.

Question 3

What are the 7 main parts of the digestive system and what do they do?

Answer 3

1. oesophagus, carries food from the mouth to the stomach
2. stomach, muscular sac with inner layer that produces enzymes. Stores and digests food esp proteins. It has glands that produce enzymes which digest protein
3. ileum, 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.
4. large intestines, absorbs water (most water thats absorbed is water from the secretions of the many digestive glands)
5. rectum, final section of intestines. The faeces are stored here before periodically being removed via the anus.
6. salivary glands, pass their secretions via a duct into the mouth. These secretions contain amylase which hydrolyses starch into maltose
7. pancreas, large gland situated below the stomach. It produces pancreatic juice. This secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch.

Question 4

How is the illeum adapted for better absorption?

Answer 4

• the inner walls of the ileum are folded into villi which gives them a large surface area
• the surface area of these vili is further increased by millions of microvilli on the epithelial cells of each villus
• this adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream

Question 5

What is egestion?

Answer 5

discharge of undigested matter leftover from the process of digestion

Question 6

Breifly explain carbohydrate digestion

Answer 6

• amylase produced in the mouth and pancreas
• amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose
• the maltose is in turn hydrolysed into alpha-glucose by maltase. (maltase is produced by the lining of the ileum)

Question 7

Explain in detail the process of carb digestion

Answer 7

1. saliva enters the mouth from the salivary glands and is throughly mixed with he food during chewing
2. saliva contains salivary amylase, This starts hydrolysing any starch in the food to maltose. It also contains mineral salts that help to maintain the pH at around neutral. This is optimum for pH for salivary amylase to work.
3. the food swallowed enters the stomach where the conditions are acidic. This acid denatures the amylase and prevents further hydrolysis of the starch.
4. after a time the food is passed into the small intestine, where it mixes with pancreatic juice
5. pancreatic juice contains pancreatic amylase. This continues the hydrolysis of any remaining starch to maltose. Alkaline salts are produced by both the pancreas and the intestinal wall to maintain the pH at around neutral so that the amylase can function.
6. muscles in the intestine wall push the food along the ileum. Its epithelial lining produces the disaccharide maltase. Maltase is no released into the lumen of the ileum but is part. of to the cell-surface membranes of the epithelial cells that line the ileum. It is referred to as ‘membrane-bound disaccharide’. The maltase hydrolyses the maltose from starch breakdown into alpha-glucose

Question 8

Explain lipid digestion

Answer 8

• lipase is produced in the pancreas hydrolysing the ester bond found in triglycerides to form fatty acids and monoglycerides.
• a monoglyceride is a glycerol molecule with a single fatty acid molecule attached
• lipids are firstly split up into MICELLES BY BILE SALTS (produced by the liver)
• this process is EMULSIFICATION and increases the surface area of the lipids so that the action of lipase is speeded up

Question 9

Explain protein digestion

Answer 9

• peptidases (proteases) hydrolyse proteins (large, complex molecules)

Question 10

What are the 3 peptidases (protease) and their function?

Answer 10

1. endopeptidase
   - hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
2. exopeptidase
   - hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides and single amino acids
3. dipeptidases
   - hydrolyse the bond between the 2 amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum