Prepared by

Kugan

Thivagar

Le Tian

Wei Tong

Jun Kai

Jun Hau

Kah Sing

*Enzymes are highly specific in their action.

*The specificity of an enzyme is due to its surface configuration (shape) according to the

lock and key hypothesis.

enzymes (lock)

active site

This shows an enzyme. It has a part that is shaped in a certain manner. This part is called the active site. The enzyme acts like a lock.

In each enzymes, there is an active site which will allow a substrate to bind with it to carry out the specific catalytic activity.

substrates (key)

A B

There are 2 different substrates , A and B. They have different shapes. A substrate can act like a key.

As each enzyme has a specific shape for its active site, only certain substrates are suitable to bind with it. Other non-compatible substrates will not be able to fit into the active site.

enzyme-substrate complex

Because of its shape, substrate A fits into the enzyme like a ‘lock and key’. They form an enzyme-substrate complex. In this way, the enzyme is able to act on substrate A.

A

When a substrate is bound to the active site of the enzyme, a temporary structure called the enzyme-substrate complex is formed .

B

Substrate B does not fit into the enzyme so no reaction takes place.

products

The enzyme acts on substrate A to form new products which are released. The enzyme remains unchanged and can used again to act on more substrates.

Once the enzyme-substrate complex is formed, the substrate molecule will be changed into one or more product molecules and are released from the complex, leaving the active site free again to accept another compatible substrate.

The formation of the enzyme-substrate complex lowers the activation energy. As a result, reaction can take place more readily to facilitate the formation of products.

En

erg

y

Level

Reaction without enzyme

Reaction with enzyme

Substrate

Enzyme

Enzyme-substrate complex

Activation energy for reaction with enzyme

Activation energy for reaction without enzyme

Enzyme regenerated at the end of reaction

Products

Progress of reactionGraph showing how the formation of the enzyme-substrate complex speeds

up a reaction

http://youtu.be/XTUm-75-PL4

http://youtu.be/E-_r3omrnxw

Enzyme W X Y

Based on Figure 1.1, complete the schematic diagram below to show the mechanism of enzyme action on a suitable substrate.

1. Figure 1.1 shows the structure of an enzyme and 3 substrates W, X and Y.

Figure 1.1

Enzyme + Substrate Enzyme-Substrate Complex

Enzyme + Product

+

substrate

+

Product

2. Figure 3 shows the diagrammatic presentation of an enzyme-catalysed reaction according to a hypothesis.

a) Which substance is the enzyme? _____________________________________________________________________________ (1 mark)

b) Name the hypothesis. _____________________________________________________________________________ (1 mark)

c) Which characteristics of enzymes can be explained by the hypothesis as shown in Figure 3? _____________________________________________________________________________________ _____________________________________________________________________________________ ___________________________________________________________________________ (3 marks) d) State 2 factors affecting activities of enzymes which are not shown in Figure 3. i) ___________________________________________________________________________ (1mark) ii) ___________________________________________________________________________ (1mark)

R

The lock-and-key hypothesis.

- Enzymes remain unchanged at the end of the reactions and can be used again.

- Enzymes are substrate specific.

- Temperature - pH

- Enzymes cancatalyse both forward and backward reactions.

Thank you!!!