Enzymes as biological catalysts 

Enzymes speed up chemical reactions by acting as biological catalysts. They catalyse metabolic reactions both at a cellular level and for the organism as a whole. 

Enzymes can affect structure in an organism as well as functions. Enzymes action can be intracellular or extra cellular. 

Enzymes are proteins. 

Have an active surge which has a specific shape. This is where the substrate molecules bind to. 

Enzymes are highly specific due to their tertiary structure. 

How enzymes speed up reactions 

Enzymes lower the activation energy needed often making reactions happen at a 

Owed temperature than they could without an enzyme. 

This speeds up the rate of reaction. 

When a substrate fits into the enzymes active site it forms an enzyme-substrate complex 

- if two sub rates molecules need to be joined being attached to the anthem holds them close together, reducing any repulsion between the molecules so they can bond more easily 

-if the enzyme is catalysing a breakdown reaction fitting into the active site puts a strain on bonds in the substrate so the substrate molecule breaks up more easily 

Model of enzyme action

The lock and key model

Enzymes only work with substrate that fit their active site. The enzyme and substrate fit like a lock and key - they have a complimentary shape 

Induced fit model

The substrate doesn't only have to be the right shape it has to make the active site change shape in the right way as well. Evidence showed that the enzyme-substrate complex changed shape slightly to compete the fit. This locks the substrate even more tightly to the enzyme. 

Enzyme properties 

Related to their structure. They usually only catalyse one reaction. The active sites shape is determine by the enzymes tertiary structure which is determined by the primary structure. If the tertiary structure of a protein is altered in any way the shape of the active site will change. This means the substrate won't fit into the active sky


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