Let's learn how enzymes work and are affected by different factors in A-Level Chemistry!
Enzymes
Enzymes are metabolic catalysts that are proteins. They have high specificity for a given substrate.
All enzymes have an active site, where the tertiary structure of the enzyme exactly matches the structure of its substrate. The substrate can weakly bind to the surface. This is so that binding can be readily reversed when the products need to leave the active site.
The bonds are usually hydrogen bonds or interactions between ionic groups. The binding may cause other bonds within the substrate to weaken, or it may alter the shape of the substrate so that atoms are brought into contact to help them to react.
After reaction the product leaves the enzyme, which is then free to start again within another molecule. Molecules that can fit on to the active site but cannot be catalysed are called inhibitors.This is called competitive inhibition.
Enzymes as Catalysts
Reactant molecules in a catalysed reaction have a lower minimum energy to react when they collide than they have in an uncatalysed reaction.The activation enthalpy is lower.
When the activation enthalpy is lower the reaction takes place more quickly.
Effect of Temperature on Enzymes
Enzyme activity rises with temperature as more molecules have enough energy to collide. Their combined energy is greater than the activation enthalpy.
At higher temperatures the enzyme is denatured and its activity falls. The tertiary structure held together by hydrogen bonds and weak dipole-dipole bonds will vibrate more vigourously and weaken or break.
Effect of pH on Enzymes
If an enzyme’s active site contains ionisable groups, the enzymes action will be affected by a change in pH.
If there is a –COOH group it will donate a H+ to the substrate. Raising the pH will turn it into –COO-.
Having changed the ionisable groups, the bonding between the substrate and the active site has changed.
Drafted by Eunice (Chemistry)
References:
https://www.genome.gov/genetics-glossary/Enzyme
https://thebumblingbiochemist.com/365-days-of-science/enzymes-and-catalysis/