Without enzymes, we would never function!
Every chemical reaction our bodies need to survive- respiration, digestion, even thinking- all depend on fast reactions maintained by enzymes.
Both chemistry and biology are mad about enzymes, so let’s get going!
1. Question: Who are they?
Answer: Well, enzymes are actually a type of protein made by cells like stomach cells.
Reminder: A protein or polypeptide is a folded polymer with a specific sequence of amino acids.
This unique arrangement of amino acids exists in a chain, which then folds and is held in place by chemical bonds, giving a unique 3D shape.
For enzymes, the final structure always includes an area designed for a specific molecule called an active site, and the shape is always specific to its function, like an enzyme for insulin needs a different shape to an enzyme for starch.
2. Question: What do they do?
Answer: They are biological catalysts!
A catalyst speeds up reactions WITHOUT BEING USED UP
They are specifically designed for certain substances meaning every active site is a unique match to a certain ingredient ('reactants' in chemistry and 'substrates' in enzyme talk).
But remember- NO FIT = NO REACTION!
3. Question: How do they work?
Answer: THE LOCK AND KEY HYPOTHESIS:
a. The correct enzyme is present for the specific reaction, with its active site being the right fit for the starting substrate.
b. The substrate binds to the enzyme in the active site to make the enzyme-substrate complex
c. From here, the enzyme has a different effect depending on the reaction, sometimes breaking down the substrate or even forming the desired product, but the enzyme always goes on to be reused.
Factors for optimal enzyme activity
The factors to consider with enzymes include their optimal temperature and pH!
There are 3 key points with TEMPERATURE:
- Every enzyme has its favourite temperature, other wise their chemical bonds break and their active sites DENATURE
- Changing the temperature will change the amount of successful molecular collisions
- Too much heat can lead to denaturation
Denaturation means the active site starts to breakdown because too high a temperature is breaking the chemical bonds, ruining the active site and slowing the reaction.
Regarding molecular collisions, the enzyme and the substrate need kinetic energy to move around so they have a better chance of hitting each other and reacting. But if the temperature dips too low, there is less movement and so less chance of successful collisions being made, slowing down the reaction.
However, it’s important to note that not every collision leads to a successful complex as sometimes the substrate goes into the active site but doesn’t react, but optimal conditions mean more collisions and so successful collisions over time are more likely, maintaining a fast rate of reaction.
This can also have a big impact on the active site shape, again because of the sensitivity of the chemical bonds between the amino acids in the folded 3D structure.
This leaves the active site vulnerable and if the pH makes a huge change outside the enzyme’s comfort zone, the active site will be denatured, and the substrate won’t be able to fit, which, you guessed it, slows the reaction right down!