JESS'S A LEVELS: Biology: Chapter 3: Enzymes: Factors that affect enzyme activity

Biology: Chapter 3: Enzymes: Factors that affect enzyme activity

In the beginning of the reaction, there are a large number of substrate molecules, so every enzyme has a substrate molecule to bind with, so rate of reaction is fastest at the beginning.
But as the reaction continues, the substrate level goes down because they are being converted to products, so there are fewer substrates to bind to enzymes, reaction rate decreases, until it completely stops when all substrates have been converted to product.

Initial rate of reaction: The rate at the beginning of the reaction, because rate is always quickest at the beginning. This can be found by drawing a tangent at the curve as close to time 0 as possible and calculating the gradient.

Rate of reaction will increase with a higher enzyme concentration if there is always an excess of substrate concentration.
Initial rate of reaction increases.
If there is an limiting factor, eg. substrate concentration, the rate will not exceed after a certain point. For substrate concentration this is because even if you increase enzyme concentration, there will only be a limited amount of substrates to bind to the enzymes, and after the point where each enzyme has a substrate to bind to, excess enzymes will be useless because each substrate already has an enzyme to bind to.
Rate of reaction slowly decreases as substrate gets converted to product and in the end the total amount of product will be the same because the same amount of substrate was used.
Effect of enzyme concentration can only be fairly measured at the beginning, because initial rate of reaction will vary the most with different enzyme concentrations.

Rate of reaction will increase with a higher substrate concentration if there is an excess of enzyme concentration.
Initial rate of reaction increases.
There are more substrates for enzymes to bind to, limited to amount of enzymes for substrates to bind to.
If more substrates are added than the amount of enzyme, each enzyme will have a substrate. The enzyme cannot work any faster, and substrates will need to wait for the enzyme to finish catalysing the first substrate.
Enzyme will be working at it's fastest possible rate, known as Vmax.

Reaction is slower at low temperature: Less kinetic energy means molecules move slowly, so there are less collisions between enzymes' active site and substrates.
Reaction speeds up as temperature increases: There is more kinetic energy, so molecules move faster therefore there are more frequent collisions.
However, at a certain temperature, enzyme will denature and stop working: Above a certain temperature, there is a large amount of kinetic energy, which also means a large amount of Vibrational energy. The structure of the enzyme molecule vibrates so much that some of the bonds holding the precise 3D shape of the enzyme molecule, especially the hydrogen and ionic bonds, start to break, This changes the shape of the enzyme, and therefore the shape of the active site, and substrates will no longer be able to fit into the active site. This is called denaturing, and is often irreversible.
Optimum temperature: Temperature that the enzyme works best and fastest in. Often the temperature before the enzyme starts denaturing.
In the human body, the optimum temperature of enzymes is our body temperature (37C), however, enzymes in different conditions will have different optimum temperatures.

pH level: Amount of hydrogen ions in the solution. The lower the pH, the higher the hydrogen ion concentration (H+). The higher the pH, the higher the Hydroxide ion concentration (OH-). Measure of acidity and basicity.
Hydrogen and hydroxide ions can interact with the R groups of amino acids by affecting the ionisation (charges) of the group.
This affects the ionic bonding between groups, which can alter the 3D structure of the enzyme molecule, therefore also altering the shape of the active site.
Small differences in pH are reversible because the bonds can be reformed, However, a pH that is very different from the optimum pH of the enzyme can denature the enzyme.
Optimum pH value: When the hydroxide and hydrogen ions positively affect the bonds in the enzyme in such a way they make the active site more suited to the shape of the substrate.