Enzymes

Defintion= Enzymes are globular proteins that catalyse metabolic reactions

Basics:

Lock and key method= Active site has identical shape to substrate (complementary)

Induced fit= due to interactions between R-groups

Catalyst=lowers the activation energy by providing an alternative pathway

Activation energy= the energy that must be put into a chemical system in order for the reaction to occur

Denaturing due to temperature:

• Increased temp.=Increased kinetic energy= Substrate and enzymes collide more= increased ESC formed
• Too much kinetic energy means that bonds holding tertiary structure together break

Denaturing due to pH:

(pH is the measure of H+ ion concentration)

• Enzymes have an optimum pH
• Outside the optimum pH H+ ions interact with R-groups on amino acids
• Breaks ionic bond (tertiary structure broken)
• Active site is permanently altered

Inhibitors:

• Are chemicals which reduce the rate of enzyme controlled reactions
• They combine with the active site so that it can no longer bind to the substrate
• The degree of inhibition increases with the concentration of the inhibitor 

Non-competitive:

• Auosteric binding site 
• Causes conformational change to the active site 
• Alters shape of active site
• Tend to be permanent binding
• Altering the concentration of substrate has no effect as inhibitor is not binding to the active site

Competitive:

• Stops enzyme binding directly as the inhibitor molecule is similar to the substrate
• Binds directly to the active site 
• Not permanent
• Increasing the substrate concentration reduces the effect of the inhibitor

Measuring the course of a reaction:

(The rate of enzyme controlled reactions can be measured in two ways)

1. Measure the rate of product formation

E.g 2H2O2---->2H2O+O2 (measure the amount of gas produced)

2. Measuring the rate of substrate breakdown 

E.g Starch----->Maltose (Take a drop of solution every minute-iodine solution)

Comparing rates of reaction:

Reaction=Different concentrations of catalase to the same volume of substrate

Problems=All lines eventually meet and measuring total volume of oxygen produced does not allow you to compare the rates of reaction

Solution= Therefore the initial rate of reaction is measured instead

Why do enzymes speed up reactions?

More enzymes present the more active sites there will be for the substrate to bind to. (As long as there is plenty of substrate available)

The effect of substrate concentration

As substrate concentration increases, the initial rate of reaction also increases (the more substrate molecules there are around the more often an enzyme's active site can bind with one). There is a point where every enzyme active site is working continuously. The enzyme is working at its maximum possible rate known as Vmax.

Calculating the initial rate of reaction:

Draw a tangent to the graph as close to 0 as possible