·
How do enzymes work?😆
- The molecules that enzymes work on are called substrate molecules. Enzymes catalyse the change of substrate molecules into product molecules better at some temperatures than others so the rate of the reaction is faster
- Enzymes don't work well above or below an optimum (best) value. This is partly why the processes in your body don't work as well when you have a fever
- Enzymes often also work best at optimum pH. Most enzymes in cells work best at about pH 7, but enzymes in the digestive system have to work well at much higher or lower pHs
- The rate of reaction catalysed by an enzyme will also increase as the concentration of substrate increases but only up to a point. Beyond that concentration, there is no further change in reaction rate.
- This is because the enzyme cannot work on the substrate any faster than this rate, so adding more substrate molecules will make no different to the rate.
Specific enzymes👓
- Another key feature of enzymes is that each enzyme will only work with the particular substrate, or a small group of similar substrates, this is a important point to note in I/GCSE Biology
- We say they are highly specific for the substrate. This feature is used to name enzymes. For example, carbohydrases catalyse the break down of carbohydrates and proteases catalyse the break down of proteins
Explaining the observations👀
- All the substrate molecules for one particular enzyme have the same 3D shape in some part of their molecules. This suggests that the shape is important in enzyme action
- Looking at the 3D shapes of enzymes and their substrates shows that the substrate fits neatly into an active site in the enzyme. The active site has a different shape in different enzymes
- Since the shape of the substrate fits tightly into the hole of the active site, this model of how enzymes work is called the 'lock and key' hypothesis
- Changing the pH or the temperature changes the shape of the active site so the substrate does not fit well. Too much change will break the bonds within the enzyme. This can change the shape so much that it denatures the enzyme and destroys the active site
Reference: https://ib.bioninja.com.au/_Media/induced-fit_med.jpeg
Drafted by Catrina (Biology)