1. Enzymes in Digestion
Text p.168

2. Syllabus Some enzymes work outside the body cells.
The digestive enzymes are produced by specialised cells in glands and in the lining of the gut. The enzymes then pass out of the cells into the gut where they come into contact with food molecules.
They catalyse the breakdown of large molecules into smaller molecules.
The enzyme amylase is produced in the salivary glands, the pancreas and the small intestine. This enzyme catalyses the breakdown of starch into sugars in the mouth and small intestine.
Protease enzymes are produced by the stomach, the pancreas and the small intestine. These enzymes catalyse the breakdown of proteins into amino acids in the stomach and the small intestine.
Lipase enzymes are produced by the pancreas and small intestine. These enzymes catalyse the breakdown of lipids (fats and oils) into fatty acids and glycerol in the small intestine.

3. Digestive system sequencing
Use cards

4. Table of digestive enzymes
Nutrient
Enzymes used
Where enzyme made
Part of digestive system in which digestion occurs
Product
Carbohydrate
(starch)
amylase
Salivary glands
Pancreas
Small intestine
Mouth
Simple sugars
(eg GLUCOSE)
Protein
Protease
Stomach
Amino acids
Lipid
(fats and oils)
Lipase
Fatty acids and glycerol

5. A cell which produces enzymes makes protein (enzymes are proteins)

6. Digestive enzymes:
Carbohydrates (polymers) are chains of identical sugar molecules (monomers). The enzyme that digests carbohydrates must be able to break the chemical bonds between the individual sugar molecules.
sugar
sites of enzyme attack
The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as glucose.
Enzymes that digests carbohydrates are known as carbohydrases.

7. Enzyme driven reaction
The digestion of carbohydrates can be represented
by the following equation.
carbohydrase
Carbohydrates
Sugars

8. Proteins and amino acids
As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different.
Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid.
Imagine a bead necklace made up of over 20 different kinds of bead.
amino acids
sites of enzyme digestion

9. Enzymes for digesting proteins
sites of enzyme attack
The enzymes that digest proteins must be able to break the chemical bonds between the different amino acids.
Enzymes that digest protein are known as proteases.
amino acids
The digestion of proteins can be represented by the following equation.
protease
Protein Amino Acids

10. Fats are also known as lipids.
Fat in our food
Fats are made up of a molecule of glycerol attached to three fatty acid molecules.
fatty acids
glycerol
site of enzyme attack
The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids.
Fats are also known as lipids.

11. Enzymes for digesting fat
The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids.
Fats are also known as lipids.
Enzymes that digest fat (lipid) are known as lipases.
Fat digestion can be represented by the following equation:
lipase
Fat Fatty Acids + Glycerol

12. Carbohydrase in saliva
Of these three enzymes, the only one that is released within the mouth is carbohydrase. This is partly because the conditions within the mouth are suitable for carbohydrase action.
It works best within an alkaline (pH > 7) environment.
The carbohydrase in saliva in combination with other digestive carbohydrases added later from the pancreas and the small intestine complete carbohydrate digestion.

13. Digestive action of the mouth - summary
Carbohydrates
Fats
Proteins
physical digestion
chemical digestion
The food could now pass down either the trachea (windpipe) or the gullet/oesophagus.
chemically and physically digested
physically digested
sugars