Enzymes Aims: Must be able to outline the role of enzymes. Should be able to describe how the process happens. Could be able to explain factors affecting enzyme function.

Enzymes Globular proteins with an active site capable of acting as catalysts. Therefore tertiary structure most important to function. Therefore any change to tertiary structure will result in a loss of catalytic function. Many proteins require other factors to aid function: –COFACTOR – metallic ions e.g. copper, zinc, iron –CO-ENZYME – organic molecule e.g. vitamin, NAD –Some co-enzymes are permanently attached – PROSTHETIC GROUP.

Enzyme Action Act by lowering ACTIVATION ENERGY required for chemical reaction to take place. Graph: Enzyme present = less energy required. Reaction takes place more readily. Increased speed of reaction (do not alter equilibrium constants).

Enzyme Action 1. Enzyme binds to it’s substrate forming an ENZYME/SUBSTRATE complex. 2. Reaction takes place and product(s) formed. 3. Enzymes emerge unchanged. 4. Enzymes can be reused. 5. Therefore enzymes are effective in minute concentrations.

Theories of Enzyme Action LOCK AND KEY Enzyme has an active site and the substrate(s) fits the site. Reaction takes place, substrate(s) released INDUCED FIT Substrate(s) bind to active site, inducing a change in the enzyme so the substrate(s) fit more easily. When closely bound, reaction takes place. Substrate(s) released, enzyme returns to original shape.

Factors Affecting Rate SUBSTRATE CONCENTRATION: Increased concentration = increased rate – increased chance of collisions Levels off at a given point V-max = maximum rate of reaction – All active sites occupied. Graph: ENZYME CONCENTRATION: Increased concentration = increased rate – more active sites available. Substrate concentration must be in excess of enzyme.

pH Enzymes have an optimum pH for maximum velocity. Graph: Small changes in pH alter H-bonds and ionic attractions = small loss of catalytic activity = decrease in reaction rate (reversible). Larger changes break disulphide bonds and even hydrolyse peptide bond – loss of 3D shape – denaturation – loss of catalytic function (Not reversible). pH changes can lead to a change in charge distribution = loss of attraction between enzyme and substrate: Diagram:

Temperature Graph: 0-40°C = increasing temperature = increasing rate of reaction – increased speed of substrate and enzyme movement = increased chance of collision °C = increasing temperature = decrease rate of reaction – atoms vibrate breaking bonds = denaturation and loss of catalytic function.

Inhibitors Chemicals that interfere with enzyme functions: COMPETITIVE – Compete with substrate for active site of enzyme – can bind permanently with enzyme. NON-COMPETITIVE – bind to part of enzyme (not active site) – prevent/reduce enzyme function.

Activity Answer the questions from pages 35 to 40 in Biozone book.