Enzymes

Enzymes are organic catalysts which speed up chemical reactions in organisms. In the absence of enzymes the chemical reactions in the cells would be so slow as virtually not to proceed at all. Enzymes speed up and control chemical reactions such as respiration and photosynthesis. There may be up to 1000 different enzymes in a single cell.

Enzymes generally work rapidly; they are not destroyed by the reaction that they catalyse. They can work in either direction. Enzymes are inactivated by excess heat and are pH sensitive. Enzymes are specific in the reactions that they catalyse.

An enzyme is a protein molecule; at its optimum temperature and pH it has a specific structure. This structure has an active site, into which a substrate molecule will fit. Changing the temperature or pH will slightly alter the structure of the enzyme, making it more difficult for some substrate molecules to fit into the active sites.

When all the active sites are working, the enzyme reaction will reach its maximum rate.

Increasing the substrate concentration will increase the rate of the reaction up to a point. Above that point further increases to the substrate concentration has no effect. Presumably all the active sites are working as quickly as they can.

Increasing the enzyme concentration will increase the rate of the reaction because there are now so many more active sites working to catalyse the reaction.

How enzymes work:

It assumed that when an enzyme works an enzyme/substrate complex is formed.

This hypothesis is called the Lock and Key mechanism. The substrate molecule e.g. starch, fits into the active site of the enzyme molecule e.g. amylase. They react together to form a product e.g. glucose. The product leaves the enzyme molecule which can on to catalyse the breakdown of another starch molecule.

References:

M.B.V. Roberts

www. bioweb.com

Catalase Enzyme Investigation:

Prior knowledge:

1. Use your CM1 notes to remind yourself about enzymes.

What do they do? What will affect the rate at which they work?

2. What is digestion and what digests the food that we eat?

3. Why do we chew our food? i. To help us swallow and ii?

4. How exactly do enzymes work? ----Use your notes and books for reference.

New Knowledge:

Catalase is an enzyme found in the liver. It breaks down molecules of harmful hydrogen peroxide into harmless water and oxygen gas.

hydrogen peroxide --------------> water + oxygen

2H₂O₂ ------------------------> 2H₂O + O₂

Potato is also a source of catalase.

Catalase Enzyme Investigation:

The problem to investigate:

P planning

What will affect the rate of hydrogen peroxide breakdown by a given amount of catalase?

1. List the factors that could affect the rate of breakdown.

2. Decide which one you will investigate.

3. What is your prediction about the factor that you will investigate?

4. What are you going to change and how do you think that this will affect the rate of the enzyme reaction?

5. Why do you think that this will happen ...... use scientific knowledge?

6. What will you keep the same? ........ Why must you keep these the same?

Pre-test your method so you can decide on the amounts that you will use and the range over which you will test your prediction.

8. Refine your plan;

What amounts will you use? What range will you test?

What exactly will you measure and how? What will you keep the same and why?

9. Draw a diagram of your apparatus.

10 Say exactly what you are going to do. What safety procedures are needed?

11. How will you make sure that your results are accurate?

12. Draw a results table.

O obtaining evidence.

1. Carry out your experiment.

2. Take your measurement accurately.

3. Record your results in the table.

A analysing and drawing conclusions.

1. What have you found out from your experiment?

2. Draw a graph with a line of best fit. What is its shape and is there a pattern?

3. What conclusions can you draw from your results? Do your results agree with your prediction and scientific knowledge or not?

4. Use your scientific knowledge to explain your results. Why did this happen, what caused it? ...Use reference books if you need to.

E evaluating evidence

1. Was you test fair and accurate? If not why not?

Have you taken enough measurements? Have you covered the whole range?

Were your results repeated? Did you get similar results when repeated?

Have you got the right sort of evidence to support your conclusion?

2. Did all your results fit the pattern or were some "out"? Which ones do you think were inaccurate? Why do you think that these are in accurate? What could have gone wrong?

3. If you did the experiment again how could you improve it?

4. If you were to take this investigation further what could you do to extend it?