IB Enzyme practical

Factors affecting Enzymes

1. Temperature2. pH3. Substrate concentration4. Enzyme concentration

The best way to understand temperature, pH and substrate concentration effects is through paying with this game....and here's another....

Factors which affect enzyme activity 1: Temperature

From: GCSE Bitesize:26.08.12

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev4.shtml

The effect of temperature

• For most human enzymes the optimum temperature is about 37°C

• Many are a lot lower. For example, cold water fish can die at 30°C since many of their enzymes denature

• Many plant enzymes have optimal temperature of 28 – 30 C

• A few bacteria in hot springs have enzymes that can withstand very high temperatures up to 100°C

• Most enzymes are fully denatured at 70°C

Factors which affect enzyme activity 2: pH

Optimum pH values

Enzyme

activity

Trypsin

Pepsin

pH1 3 5 7 9 11

The effect of pH

• The pH of a solution affects the shape of an enzyme• At non-ideal pH values, the active site is distorted

and the substrate molecules will no longer fit • Extreme pH levels will produce denaturation• Many enzymes have pH values which are NOT

neutral (pH = 7): e.g. pepson, trypsin in the stomach and gut

Denaturation

Denaturation is a change in the shape of an enzyme which prevents it from fulfilling its function.

Enzymes (and other proteins) can be denatured by heat, pH changes, or certain chemicals

NB: Denaturation is not the same as ‘killing’ – proteins and enzymes are not living things, so can’t be killed!

What does ‘enzyme denaturation’ mean?

Factors which affect enzyme activity 3: Substrate and enzyme concentration

From: http://www.skinnersbiology.co.uk/enzyme.htmAugust 26th 2012

Substrate concentration: Enzymic reactions

Reaction velocity

Substrate concentration

Vmax

Celebrity enzymes

1. Amylase2. Pepsin3. Pectinase 4. Catalase

Amylase

• all about amylase...• amylase digestion

Pepsin

• All about pepsin• pepsin working in the st

omach

Pectinase • Pectinase is widely used to

increase the yield in fruit juice extraction, and also to make juice clear rather than cloudy

• Pectinase breaks down the pectin chains in the middle lamellae connecting fruit cells

• Pectinases and amylases can both break down these insoluble polysaccharide compounds within fruit cells, releasing soluble sugars which clarify the juice producing a clearer, sweeter product.

Catalase

• Better, stronger, faster• A biological enzyme

present in all living cells exposed to oxygen

• ‘Extremely high turnover number’

• Catalase instantaneously degrades hydrogen peroxide into water and oxygen

What does hydrogen peroxide do in the body?

• H2O2 is a strong oxidising agent produced as a by-product of metabolism

• Can damage cells – can break DNA, cell membrane, proteins and lipids

When do we use hydrogen peroxide commercially?

• Bleach• stain remover• Wound treatment (?)

Where is Hydrogen peroxide located?

Your Research Challenge

Investigate the effect of yeast (saccharomyces cerevesiae) catalase enzyme concentration on) the rate if breakdown of hydrogen peroxide using quantitative methods

p. 44 of your IGCSE book

What is the hypothesis you are going to test?

Research Question:

Does catalase concentration affect the rate at which catalase breaks down H2O2?

What is the hypothesis you are going to test?

Quantitative experiment

How can we measure the rate at which catalase breaks down H2O2?

Does enzyme concentration affect the rate at which catalase breaks down H2O2?

Working Observation

Experimental Design

• Working Observation: As enzyme concentration increases, the rate of breakdown of H2O2 by catalase should increase

• (Null hypothesis: a change in enzyme concentration has no effect on the rate of H2O2

decomposition by catalase does not change)

• (Alternative hypothesis: enzyme concentration is directly related to the rate of H2O2 decomposition by catalase )

Quantitative experiment• How can we measure the rate at which

catalase breaks down H2O2?

• Quantity of oxygen produced over a set time (volume, %, pressure)

Starting questions

1. What apparatus and other materials will you need for your experiment?

A few starting questions:

1. How exactly will you ‘measure’ the reaction between H2O2 and catalase??

How exactly will we ‘measure’ the reaction between H2O2 and catalase?

We will measure the rate of reaction between catalase and hydrogen peroxide indirectly by measuring the pressure change in a closed chamber, using a Vernier Gas pressure probe

Data Collection

Dependent Variable

Independent Variable

Controlled variables

Uncontrolled variables

Catalase experiment

Dependent Variable Gas pressure produced by in closed chamber

Independent Variable Catalase concentration %

Controlled variables pHTemperature

Substrate concentration

Uncontrolled variables Human error – timing and measurement

Catalase experiment

Starting questions:

3. Can you think of other factors that may affect enzyme activity?

• Substrate concentration• Temperature• pH• Human error

Starting Questions…

• How will we record our data?• “Results table?

…and a few questions about study design…

1. Which concentrations should we test? – and why?

2. Do you want this to be a controlled experiment? What will be the control group?

3. How many test groups should we have?

4. How many times will you repeat each test?

5. How will we prepare our stock catalase solutions?

Predictions/ Conclusions

• Make a prediction about your conclusions. • Do you expect to find support for your

hypothesis? • Why or Why not?