1. Unit 3 Science Investigation Skills
Topic D: Enzymes in action
Lessons 2–4

2. Lesson 2 Learning objectives
To present your research on levels of protein structure.
To describe the structure of an enzyme.
To explain the interaction of an enzyme with its substrate (the lock and key model).
To discuss the skills needed when planning an experiment to investigate the effects of pH and temperature on egg albumen.

3. Present your research on the levels of protein structure.

4. Check your learning
For each of the following statements, say whether they refer to primary, secondary, tertiary or quaternary structure of proteins:
Some regions of a polypeptide form regular structures known as alpha-helices and beta-pleated sheets.
The amino acids in a polypeptide are linked together in a chain by peptide bonds.
Some proteins consist of more than one polypeptide chain linked together.
Enzymes often consist of a single polypeptide folded into a globular shape.

5. The effects of pH and temperature on proteins
Proteins are susceptible to
structural changes caused
by changes in pH or
temperature, which can
affect the various bonds
and interactions between
amino acid R groups.
A major, irreversible change
is known as denaturation.

6. Enzymes as protein molecules
The structure of an enzyme is formed and maintained by various types of interactions between different amino acid R groups.

7. The lock and key model
The lock and key model describes the way that a substrate molecule will only fit into the active site of a specific enzyme. This specificity enables metabolic reactions to be carefully regulated within an organism. The enzyme and substrate form a complex and the formation of products is catalysed. At the end of the reaction, the enzyme remains unchanged and ready to receive further substrate molecules.

8. Planning a practical investigation
You will be investigating the effects of different pHs and temperatures on egg albumen. Egg albumen is the mixture of proteins found in egg whites. The most abundant protein in the mixture is ovalbumin (54%), and another protein of interest is the enzyme lysozyme (3.5%).

9. Things to consider Choice of equipment Hazards and risks Methods
The variables
How to record results and observations

10. Variables You will need to identify:
the independent variable(s) What will you change in order to cause an effect? What is a suitable range of values to use, to allow you to observe any effects?
the dependent variable(s) What will you measure or observe in order to discover any resulting effects?
the control variables. What will you keep unchanged to ensure that any effects are due to changing the independent variables only?

11. Equipment You will be provided with: egg albumen
solutions of different pH
thermometers
test tubes
water-baths at different temperatures
stopwatch.
You need to consider how this equipment would be used for these investigations and whether any additional equipment would be needed.

12. Methods For each investigation, you need to consider:
how you will set up the equipment
suitable values of the independent variables to use in order to assess their effects
how many times you would carry out each investigation
how to control any unwanted variables (control variables)
how you will assess/measure the effects produced.

13. Risk assessment
When you have planned a method, you will need to carry out a risk assessment.
You will need to identify:
any potential hazards (procedures, equipment or chemicals that could cause harm)
who could be harmed
the risk (probability or likelihood) that these hazards could cause harm
how to minimise the risk of any hazard causing harm
procedures for dealing with any incident or harm caused.

14. Results and observations
You will need to identify how you will record the results/observations of your investigations. You will also need to consider how you will present your data.

15. Lessons 3 and 4 Learning objectives
To carry out your investigations into the effects of pH and temperature on egg albumen
To work safely
To record your results and observations in tables
To write valid conclusions