Edexcel Biology- Unit 1 Topic 2 Enzymes

How enzymes work and what they do

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  • Created by: Megz
  • Created on: 10-04-10 12:37

Biological Catalysts

Enzymes catalyse metabolic reactions in your body e.g digestion and respiration

-Anabolic reactions build up new chemical substances 'ana' means build up

-Those that break down substances are catobolic reactions 'cata' means break down

-These two processes result in what is known as metabolism

Enzymes are specific to a reaction

-Temperature and pH conditions change the enzymes structure/shape

-Intracellular is when an enzyme work inside cells like DNA polymerase whereas extracellular is enzymes that works outside the cell membrane like digestive enzymes.

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Function of Enzymes

Enzymes increase the rate of reaction by lowering the activation energy- To do this the enzyme forms a complex with the substrate

  • substrate+enzyme= enzyme/substrate complex= enzyme and product
  • After the enzyme has catalysed a reaction it is free for more use

-The lock and key hypothesis gives us a model to help us understand what happens; at the active site the substrate combines with the enzyme which has a specific shape

However, it is now thought the lock and key mechanism is a simplified version of what can happen

-According to evidence from x-ray crystallography, chemical analysis of active sites, the site is not as rigid as suggested; the induced fit hypothesis shows us that the active site is still specific in its shape and arrangement but rather more flexible

-When the substrate enters the active site, the enzyme moulds around it to form the complex

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Enzymes can only change the rate at which the reaction happens not change the end products that are formed

Small amounts are needed as they aren't used up

Enzymes have great specificity

The number of substrate molecules affects how long the reaction takes

Optimum temperature is when the enzyme no longer works because it is denatured- too high but too low it is deactivated

Denatured because the molecules have more kinetic energy and so vibrate more which breaks the hydrogen bonds in the active site. Deactivated because the molecules have less energy so the rate of reaction decreases.

Different enzymes work at different pHs because of the bonding arrangement which holds the shape so their activity changed.

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Very nice revision tool. Thanks, it realy helped with the definitions. Just please check the definition for optimum temperature. It is the temperature the enzyme works best at, not the one where the enzyme no longer works.

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