Enzymes

B3a

What are the uses of enzymes?

Why do we need to break down food?

Digestive system Blood

OBJECTIVES

Key Objective Describe the factors affecting enzyme action

C/D State what enzymes are and their function in the body Describe how changing temperature and pH will change the

rate of reaction of an enzyme-catalysed reaction

B-A* Explain the specificity of enzymes in terms of the ‘lock and

key’ mechanism. Explain how enzyme activity is affected by pH and

temperature

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

The lock and key model

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.

Your Task …

You are going to look at the effect of temperature on the enzyme amylase. In this experiment, iodine is used to test whether the starch has been broken down. You will need to find out the speed of the reaction over a series of at least five temperatures, starting at 20°C. On the start menu find ‘science investigations 1’. Click on Biology > The breakdown of starch by amylase. Reset the experiment (reset button at top) Click on ‘test’ to check for the presence of starch – you will need to

change the reaction time by a minute to get your results over a set time.

Blue = Orange =

Try this at different temperatures – what do you think will happen?

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.

PLENARY

Enzyme properties worksheet

Enzymes are chemicals produced by the body to help _______. When they react with food they break it down into ______ pieces which can then pass into the ______:

Carbohydrase (produced in the mouth, pancreas and small intestine) breaks _______ (a carbohydrate) down into glucose:

Protease (produced in the stomach, pancreas and small intestine) breaks _______ down into amino acids:

Lipase (produced in the pancreas and small intestine) breaks fats (_____) down into fatty acids and glycerol:

Words – blood, lipids, proteins, digestion, starch, smaller

Blo

od

stre

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Digestive enzymes are the chemicals that break large insoluble food molecules into smaller soluble molecules.

Digestive enzymes are classified by the type of food that they affect, so there are three main types:

Different types of digestive enzymes

carbohydrase – breaks carbohydrate into smaller sugars.

protease – breaks protein into amino acids.

lipase – breaks fat into fatty acids and glycerol.

Carbohydrates are chains of identical sugar molecules.

The digestive enzymes called carbohydrases break the chemical bonds between the individual sugar molecules in each carbohydrate chain.

carbohydrase

long carbohydrate

moleculesugar

molecules

Enzymes and carbohydrate digestion

Proteins are made up of amino acids. There are 20 different types of amino acids.

Proteins are digested by digestive enzymes called proteases. These enzymes work in an acidic environment to break proteins into smaller amino acids.

protease

long protein molecule

amino acid molecules

Enzymes and protein digestion

Fats are digested in two stages:

Firstly, bile (released by the gall bladder) allows the fat to “mix” with water by breaking the fat into smaller droplets. This is called emulsification.

Secondly, the digestive enzyme lipase breaks each fat molecule into the smaller glycerol fatty acid molecules .

bile

lipase +

fat molecule glycerol fatty acids

Enzymes and fat digestion