Enzymes Enzymes are proteins that act as biological catalysts They 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 Check Catalyst: 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 specificity Induced 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 substrate Only fits its particular substrate

What are the models used to describe enzyme action?

Lock and key mechanism Induced fit mechanism

The induced fit theory The 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 enzymes 1. All enzymes are proteins 2. Enzymes are denatured (inactivated) by extreme temperatures 3. 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. Temperature 2. pH 3. Substrate concentration 4. 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:

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 Enzy me activit y Tryps in Pepsi n pH

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: August 26 th 2012

Substrate concentration: Enzymic reactions Reaction velocity Substrate concentration V max

Celebrity enzymes 1. Amylase 2. Pepsin 3. Pectinase 4. Catalase

Amylase all about amylase... amylase digestion

Pepsin All about pepsin pepsin working in the stomach pepsin working in the stomach

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? H 2 O 2 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 H 2 O 2 ? What is the hypothesis you are going to test? Quantitative experiment How can we measure the rate at which catalase breaks down H 2 O 2 ?

Does enzyme concentration affect the rate at which catalase breaks down H 2 O 2 ? Working Observation Most enzymes have maximal efficacy at a specified temperature (somewhere between 30 – 37 0 C in mammals) Temperature extremes should reduce the rate at which catalase breaks down H 2 O 2

Experimental Design Working Observation: As enzyme concentration increases, the rate of breakdown of H 2 O 2 by catalase should increase (Null hypothesis: a change in enzyme concentration has no effect on the rate of H 2 O 2 decomposition by catalase does not change) (Alternative hypothesis: enzyme concentration is directly related to the rate of H 2 O 2 decomposition by catalase )

Quantitative experiment How can we measure the rate at which catalase breaks down H 2 O 2 ? 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 H 2 O 2 and catalase??

How exactly will we ‘measure’ the reaction between H 2 O 2 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 pH Temperature 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?