Chapter 4.4 : Chemical Composition of Cells (ENzYmes)

Define an enzyme.

An enzymes is  an organic catalyst that accelerates the rate of a

biochemical reaction. It is made up of protein.

Explain why enzymes are needed in life processes

Every cell carries out thousands of biochemical reactions at the same time. Enzymes are biological catalysts that regulate almost all the cellular reactions. Enzymes are biological catalysts that speed up biochemical reactions in the cells.

List the general *Characteristic of enzymes

 - enzyme has an active site.

- which has a specific shape.

- active site is rigid.

- the shape is complementary to the shape of the substrate (as key fits into 

  a lock).

- forming an enzyme-substrate complex

- reaction takes place and the products are released.

- Enzymes work very rapidly

- Enzymes are not destroyed by the reactions which that catalyse

- Enzymes can work in either direction

- Enzymes are extremely specific

-  Enzymes are denatured by high temperature

-  Enzymes are sensitive to pH

*ReMinDer! -please refer the diagram

Figure 1 shows a biochemical reaction between an enzyme molecule and

            a substrate

• An enzyme has an active site which allows only specific substrate molecules to combine with it.
• The positioning of the substrate on the active site in the enzyme is accurate and precise, and is similar to a ‘lock and key’
• The substrate molecule (key) combines with the active site of the enzyme (lock) to form an unstable enzyme-substrate complex
• The product of the reaction is released from the active site of the enzyme.
• The enzyme can be reused

A temperature is a factor  that affect the activity of enzyme ; explain

- temperature increase, the rate of reaction increase.

- rate of reaction increases due to the increased kinetic energy of the

  substrate and enzyme molecules.

- these molecules move faster, colliding each other makes the rate of  

  reaction faster

- the increased rate of reaction would reach it limit when the optimum

  temperature is reached.

- this is the limit for the substrate and the enzyme to react optimally.

- temperature increased beyond /reach optimum temperature, the rate of

  reaction decrease.

- the bonds that holding the molecules break up

- causing the three dimensional shape of the enzyme molecule to be

   altered.

- the active site of the enzyme will no longer fit the subtrate.

- the enzyme is denatured and the rate of reaction decreases.