Feb 21
In this free sample of the science revision tuition programme, we discuss Enzymes and their Structure.

Enzymes are made of proteins, and proteins are made of long chains of amino acids. These get folded into specific shapes to allow the enzyme to perform its role in the cell.

Enzyme Active Site and Specificity

Every enzyme has an active site; this is the site that catalyses the reaction. The active site is a specific shape for the substrate.

Each substrate, such as starch, has a specific shape and only the enzyme that breaks down starch – amylase has an active site that will fit starch into it. They usually only catalyse one reaction.

Lock and Key Model and Induced Fit Model of Enzyme Action

This simplified model is called the lock and key model of enzyme action. The enzyme is like the lock with a specific shape for the substrate that is like the key. The enzyme is not rigid in its structure and changes shape a little as the substrate is attached. The enzyme closes around the substrate to make a tighter fit – this is called the induced fit model.

Denaturing - Temperature and pH

As bonds hold enzymes together, changes to their environmental conditions can break these bonds and therefore change the shape of the active site. This changing of the active site denatures the enzyme, and they stop working. Two factors that can change the active site shape of an enzyme are temperature and pH.

When we increase the temperature of a substance, we increase the kinetic energy. This kinetic energy increases the number of successful collisions between the enzyme and substrate. Up to a point, the enzyme has an optimum temperature at which it will work.

After that, the increase in temperature breaks the bonds that hold the enzyme into its specific shape, changing the shape of the active site. This is called denaturing. Remember that enzymes are not denatured at low temperatures but have less kinetic energy.

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