Enzymes in Digestion

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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.

Digestive system sequencing

• Use cards

Table of digestive enzymes

Nutrient Enzymes used Where enzyme made

Part of digestive system in which digestion occurs

Product

Carbohydrate(starch)

amylase Salivary glandsPancreasSmall intestine

MouthSmall intestine

Simple sugars (eg GLUCOSE)

Protein Protease StomachSmall intestine

StomachSmall intestine

Amino acids

Lipid(fats and oils)

Lipase PancreasSmall intestine

Small intestine Fatty acids and glycerol

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

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.

The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as glucose.

Enzymes that digests carbohydrates are known as carbohydrases.

Digestive enzymes:

sugar

sites of enzyme attack

The digestion of carbohydrates can be represented by the following equation.

SugarsCarbohydratescarbohydrase

Enzyme driven reaction

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.

Proteins and amino acids

Imagine a bead necklace made up of over 20 different kinds of bead.

amino acids sites of enzyme digestion

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.

proteaseProtein Amino Acids

Fat in our food

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.

Fats are made up of a molecule of glycerol attached to three fatty acid molecules.

fatty acids

glycerol

Fat digestion can be represented by the following equation:

lipaseFat Fatty Acids + Glycerol

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.

Enzymes for digesting fat

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.

Carbohydrase in saliva

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.

The food could now pass down either the trachea (windpipe) or the gullet/oesophagus.

sugars

chemically and physically digested

physically digested

physical digestion

chemical digestion

CarbohydratesFatsProteins

Digestive action of the mouth - summary