Revision lesson on enzymes

AQA Unit 2 Additional Biology

What are enzymes and what do they do?

Enzymes are- Protein molecules (made up of amino acids) Biological catalysts (Increase the speed of

chemical reactions) Specific (Each one catalyses one particular

reaction) Reusable (Can be used again and again) Affected by temperature and pH. Found in animals, plants and microorganisms.

2 main types of enzymes

Catabolic enzymes which (break down) large molecules into smaller moleculese.g. digestion of starch by the enzyme amylase into glucose.

Anabolic enzymes which (build up) small molecules to form larger moleculese.g. production of glucose during photosynthesis from carbon dioxide, water and light.

Enzymes and activation energy

Chemical reactions take place when particles collide with enough energy.

The minimum amount of energy required is called the activation energy.

Enzymes lower the amount of activation energy required, so the reaction can proceed at a greater rate.

Structure of an enzyme molecule

Enzymes are proteins made up on long chains of amino acids.

These long chains fold to produce a special shape which is vital for the enzyme‘s function.

Active Site

How enzymes work

Step-by-step Shape of the enzyme’s active site is

complimentary to the shape of one particular substrate.

The two bind together to form an enzyme-substrate complex.

The reaction between them take place rapidly. The products are released from the enzyme’s

active site. Complete Qu 1-8 on your worksheet.

Factors affecting enzyme action - Temperature

Enzymes work faster as the temperature increases up to 40oC, but are eventually denatured at about 60oC.

This is because the shape of the active site is lost.

Factors affecting enzyme action – pH

Each enzyme works best at a particular pH. This is known as the optimum pH.

Extremes of pH will cause the active site to denature.

Answer Qu 8- 11 on your worksheet

Enzymes in digestion

Enzymes break down large insoluble food molecules into smaller, soluble ones which can be absorbed through the small intestine wall to enter the bloodstream.

Different parts of the digestive tract have different pH conditions to enable different enzymes to work.

The main groups of digestive enzymes

Lipase enzymes digest fatty substrates.

Protease enzymes digest protein substrates.

Carbohydrase enzymes digest carbohydrate substrates.

Substrate Enzyme Product Where enzyme produced

Optimum pH

Starch Amylase (a carbohydrase)

Glucose Salivary glands & pancreas

pH7

Protein Trypsin(a protease)

Amino acids

Stomach, pancreas, & small intestine

pH3

Lipids Lipases (fats)

Fatty acids & glycerol

Pancreas pH8

The action of bile

It’s produced by the liver and is stored in the gall bladder which, squirts it into the small intestine.

It’s alkaline to neutralise acidic chyme coming from stomach.

It emulsifies fats to break them into smaller droplets which increases the surface area for lipase enzymes to work.

Commercial use of enzymes

Product Enzymes Explanation

Biological washing powder

Lipases and proteases.

Digest biological stains off clothes.

Baby food Proteases Pre-digest protein to make digestion easier for babies.

Slimming foods Isomerase (carbohydrase)

Converts glucose into fructose (less of which is needed to sweeten food).

Complete Qu 12- 17on worksheet.