2.5 Enzymes Understanding: Enzymes have an active site to which specific substrates bind Enzyme catalysis involves molecular motion and the collision of substrates with the active site Temperature, pH and substrate concentration affect the rate of activity of enzymes Enzymes can be denatured Immobilized enzymes are widely using in industry Skills: Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes Experimental investigation of a factor affecting enzyme activity Applications: Methods of production of lactose-free milk and its advantages Nature of science: Experimental design: accurate quantitative measurements in enzymes experiments require replicates to ensure reliability

Enzyme structure Proteins that work as a catalyst. Speed up chemical reactions without being altered themselves. Understanding: Enzymes have an active site to which specific substrates bind

Enzyme structure Enzymes only catalyze one reaction Thousands of reactions take place in a cell Majority need to be catalyzed. Organisms produce thousands of enzymes Enzymes are specific Understanding: Enzymes have an active site to which specific substrates bind

Specificity Enzymes have an active site Specific to a substrate Only that substrate can fit Cannot catalyse other reactions Understanding: Enzymes have an active site to which specific substrates bind

Three Stages Substrate binds to active site of enzyme. 2. Substrates change into different chemical substances 3. These products separate from the active site, leaving it vacant for substrates to bind again Understanding: Enzyme catalysis involves molecular motion and the collision of substrates with the active site

Collisions Random movement of substrates and enzymes Means there are collisions Only bind together if they are aligned exactly Dissolving in water allows more collisions Understanding: Enzyme catalysis involves molecular motion and the collision of substrates with the active site

Denaturation Structure can be irreversibly altered by certain conditions. Active site shape changes – substrate can no longer bind Understanding: Enzymes can be denatured

Your Experiment Each of you will be investigating one of the following factors affecting the rate of reaction of enzymes. Temperature pH Concentration of substrate You need to plan and carry out this experiment (each group has a different variable) You will then present your results Skills: Design of experiments to test the effect of temperature, pH and substrate concentration on the activity of enzymes Experimental investigation of a factor affecting enzyme activity Understanding: Temperature, pH and substrate concentration affect the rate of activity of enzymes

Rate of Reaction How much of a product is formed OR how much a reactant is used up Many things affect the rate of reaction. High rate of reaction = fast reaction Low rate of reaction = low rate

Volume of gas measured with a gas syringe or measuring cylinder Rate of Reaction Measure the mass of a substance (usually start and end – hard to find midpoints) Volume of gas measured with a gas syringe or measuring cylinder (can find midpoints) Rate of reaction = Amount of product formed OR reactant used Time taken

Example If 24 cm3 of hydrogen gas is produced in 2 minutes what is the mean rate of reaction?

Example If 24 cm3 of hydrogen gas is produced in 2 minutes what is the mean rate of reaction? 24/2 = 12cm3 hydrogen/min

Different enzymes have a different optimum pH Some like more alkali, some more acidic Too acidic or alkaline = denature and active site changes shape Closer to optimal pH = increased enzyme activity

Increase in temperature means more kinetic energy Enzymes and substrate move around more More collisions Optimal temperature – this is at a maximum Past optimal temperature = denaturation and active site changes shape No enzymes can fit into active site

More substrate = more change collisions More chance of enzyme substrate complex Gets to a point where all enzymes are being used to the max No available active sites Unless increase concentration of enzymes as well Plateau but does not decrease

Immobilised Enzymes Attach enzymes to another material Enzyme movement is restricted What are the advantages? Understanding: Immobilized enzymes are widely using in industry

Commercially Used Understanding: Immobilized enzymes are widely using in industry

Immobilised Enzymes Less likely to denature Can be re-used again and again Do not contaminate end product Do not need to filter end product Can stop and start the reaction quickly But… Requires extra time & money to make them Extra equipment to make them Reduction in reaction rate as there will be fewer collisions Understanding: Immobilized enzymes are widely using in industry