What’s the missing link?What is the link between digestion, photosynthesis, bread, wine and washing powder?

They all depend on enzymes.

EnzymesLearning Objectives• To describe the optimum

conditions for enzymes.• To describe the function of

enzymes in the digestive system. • To explain that enzymes are

specific, using the lock and key model.

Your cells are chemical factories..

• 100’s chemical reactions are happening in cells all the time

• Need to be very controlled • Catalysts can help alter the speed of a

chemical reaction• They are not change or used up in the

reaction• Catalysts are specific to one type of reaction• Enzymes are biological catalysts – they help

speed up chemical reactions in our cells• They are Proteins!

Jobs for enzymes

• Enzymes catalyse only one type of reaction each – ie they are SPECIFIC

• They bind to specific reactants known as substrates.

• Enzymes are involved in:– Building large molecules from lots of smaller

ones– Changing one molecule into another– Breaking down large molecules into smaller

ones

Enzymes are proteins! So what are they made of?

What are enzymes made of?Enzymes are protein molecules, and so are made up of amino acids. Most enzymes contain between 100 and 1,000 amino acids.

These amino acids are joined together in a long chain, which is folded to produce a unique 3D structure.

Examples where enzymes are used:

• DNA replication: Help copy a cell’s DNA before it divides by mitosis or meiosis.

• Protein Synthesis: Hold amino acids in place and form the bonds between them.

• Digestion: Help to digest food molecule's

How do they work?

• Every enzyme has something called an active site, this is the region where the substrate joins onto. Enzymes only attach to specific substrate molecules. Enzymes only work when there is an exact fit with the substrate. This is known as the lock and key mechanism.

The lock and key model

Enzymes work best at specific conditions

Optimum Temperature

Optimum Temperature• As the temperature increases, so does the rate of

reaction. But very high temperatures denature enzymes.

• The graph shows the typical change in an enzyme's activity with increasing temperature.

• The enzyme activity gradually increases with temperature until around 37ºC, or body temperature.

• Then, as the temperature continues to rise, the rate of reaction falls rapidly, as heat energy denatures the enzyme

Optimum pH

Optimum pH • Changes in pH alter an enzyme’s shape.• Different enzymes work best at different pH

values.• The optimum pH for an enzyme depends on

where it normally works.• For example, intestinal enzymes have an

optimum pH of about 7.5.• Enzymes in the stomach have an optimum pH

of about 2.

Denatured enzymes• Enzymes can be denatured by high

temperatures and extremes of pH. Both high temperatures and extremes of pH change the bonds between amino acids in the enzyme, so changing its shape.

• Enzymes work slowly at low temperatures too – but this is because the substrate molecules have less energy and move into the active site more slowly. This is not a permanent change.

There is one more way to affect the rate of an enzyme controlled reaction

Measuring the Rate of an Enzyme Controlled Reaction

• Amylase- Enzyme that breaks down starch• Starch- Substrate for amylase • Iodine- Turns a blue black colour when

starch is present.

Using these chemicals plus any lab equipment of your choice describe a simple method to measure the rate of an enzyme controlled reaction.

Write it as numbered steps for how you would do it.

How you would do it

1. Amylase catalyses the breakdown of starch, so you can time how long it takes for the starch to disappear.

2. To do this. Take a drop of amylase and starch mixture, and put it onto a drop of iodine solution on a spotting tile. Record the colour change- it’ll turn blue black if starch is present. Note the time when the iodine solution no longer turns blue-black- the stanch has then been broken down by the amylase.

3. You can use the times to compare reactions rates under different conditions.

We know how to measure the rate, but then how can we change the

rate?• To investigate the effect of

temperature- put test tubes into water baths at a range of temperatures.

• pH- Different pH buffers• Substrate concentration- vary

concentrations of starch.

Questions

1. What is a catalyst?2. Explain why enzymes are needed in the

body.3. How can the rate at which enzymes work

be altered?4. Small molecules often dissolve easily in

water then larger ones. Explain as fully as you can why enzymes are used in laundry detergents. Include proteins, catalysts and enzymes in your answer.