Chapter 3. Enzymes [SHS]

Enzymes are protein molecules which can define as biological catalysts
Catalyst speeds up a chemical reaction, but remain unchanged at the end of the reaction.

Enzyme molecules have an active site.
The active site on an enzyme is a region, usually a cleft or depression, to which another molecule or molecules can bind.

How an enzyme works

All enzymes have certain properties
* All enzymes are protein, but not all protein is enzyme. It’s a functional protein not a structural protein
* Enzymes are catalysts, speeds up a chemical reaction, but remain unchanged at the end of the reaction.
* Enzymes are inactivated by high temperatures, this because they are proteins, which are damaged by temperatures above 40’C
* Enzymes work best at a particular pH, most enzymes work best at a pH about 7, this because they are proteins, which are damaged by very acid or very alkaline conditions
* Enzymes are specific, Each type of enzyme will usually act on only one type of substrate molecule. This is because the shape of the active site will only allow one shape of molecule to fit.

Initial rate of reaction
The rate of enzyme controlled reaction is always fastest at the beginning, because at the beginning there are a large number of substrate molecules.

The rate of the reaction will depend on how many enzyme molecules there are, and the speed at which the enzyme can convert the substrate into product, release it, and bind with another substrate molecule.

Initial rate of a reaction increases linearly with enzyme concentration

Initial rate of a reaction also increases linearly with substrate concentration at the beginning but when the enzyme all occupied then it will reach constant

Enzyme inhibitors
Competitive inhibitors
Inhibitors can bind to active site of the enzyme compete with the substrate. If the inhibitors concentration higher than the substrate then the inhibitors win the competition and inhibit the enzyme work vise versa. It is said to be reversible (not permanent) because it can be reserved by increasing the concentration of the substrate.


Non-competitive irreversible inhibition

The inhibitors can permanently bonded with the active site and therefore cause a permanent block to the substrate. No competition occurs as it does not matter how much substrate is present.

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