EnzymesEnzymes are proteins that act as

biological catalystsThey lower the activation

energy of a specific chemical reaction

Catalysts – speed up the chemical reaction and are not changed by the reaction

Lowering the activation energy has a profound effect on how rapidly the reaction is completed

Enzymes: Vocabulary CheckCatalyst: A substance that speeds up a chemical

reaction without itself being changed

Enzyme: A biological catalyst that is usually a protein

Substrate: The reactant(s) upon which an enzyme has its action

Product: A substance that results from a chemical reaction

Enzymes Lower Activation Energy

What are enzymes? Enzymes are typically

proteins Enzymes are specific Enzymes act as

catalysts to speed up the rate of reaction of a biological process

Enzymes are not used up by the reaction they catalyse

Enzymes change substrates into products

How do enzymes work?Substrate specificityInduced fit versus Lock and key mechanism

Enzymes have active site (s)

An intricate pocket or cleft – a 3-dimensional entity – structurally tailored to accept a particular substrateOnly fits its particular substrate

What are the models used to describe enzyme

action?

What are the models used to describe enzyme

action?

Lock and key mechanismInduced fit mechanism

The induced fit theoryThe substrate plays a role in determining the final shape of the enzyme and that the enzyme is has some flexibility. This explains why certain compounds can bind to the enzyme but do not react because the enzyme has been distorted too much. Other molecules may be too small to induce the proper alignment and therefore cannot react. Only the proper substrate is capable of inducing the proper alignment of the active site

Induced fit in a moment....

Naming Enzymes (the official classification)

Naming Enzymes (simplified classification)

Enzymes can be named according to the type of reaction that they catalyse Carbohydrases Lipases Proteases

Enzymes can be named according to the substrate the interact with:

Maltase Sucrase

Some enzymes just have individualised names: Pepsin

Trypsin

Catalase

Key properties of enzymes1. All enzymes are proteins2. Enzymes are denatured (inactivated) by extreme

temperatures3. Enzymes work best at a particular temperature

(which depends on the organism)4. Enzymes work best at a particular pH (which

depends on the organism)5. Enzymes are catalysts (not degraded, ccan be

used over and over again)6. Enzymes are specific

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

enzymeAt non-ideal pH values, the active site is

distorted and the substrate molecules will no longer fit

Extreme pH levels will produce denaturationMany enzymes have pH values which are NOT

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

DenaturationDenaturation 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 sto

mach

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

What does hydrogen peroxide do in the body?

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

Can damage cells

Instantaneously broken down by catalase

What is hydrogen peroxide Bleach

stain remover

Wound treatment (?)

Where is Hydrogen peroxide located?

What is catalase? A biological enzyme present

in all living cells exposed to oxygen

‘Extremely high turnover number’

Catalyses the decomposition of hydrogen peroxide to water and oxygen

Your Research Challenge

Investigate the effect of enzyme concentration on yeast (saccharomyces cerevesiae) catalase enzyme activity 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 experimentHow 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

Most enzymes have maximal efficacy at a specified temperature (somewhere between 30 – 37 0C in mammals)

Temperature extremes should reduce the rate at which catalase breaks down H2O2

Experimental DesignWorking 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 experimentHow can we measure the rate at which catalase breaks

down H2O2?

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

Starting questions1. 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 % of oxygen 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/ ConclusionsMake a prediction about your conclusions.

Do you expect to find support for your hypothesis?

Why or Why not?