Investigation into the effect of enzyme concentration on the rate of hydrogen peroxide breakdown.

GCSE Science

Page 26/04/2007

AS Biology

Practical write up

Introduction

Enzyme - any group of complex proteins produced by living cells and acting as

catalysts in biochemical reactions

The brothers Hans and Eduard Buchner, who were at the time studying yeast for medical purposes, discovered enzymes in 1897. Enzymes are essential to all living organisms, as they act as catalysts to allow chemical reactions to take place within cells at low temperatures, usually between 4°C and 60°C. They do this by lowering the energy needed to start a reaction, this is known as ‘activation energy’.

Enzymes attach to substrate becoming enzyme substrate complex. They then alter the enzyme substrate complex into product and an enzyme. The enzyme is unaffected in the process and is then ready to accept more substrate. Enzymes have a specific tertiary shape that allows only a specific substrate to fit into the active site. The active site is the area of the enzyme that the substrate binds to be altered into product.

enzyme + substrate enzyme substrate complex product + free enzyme

An example of this is the enzyme ‘catalyase’. This enzyme is essential to organisms as it converts hydrogen peroxide into water and oxygen. Hydrogen peroxide is formed in the cell as a by-product of biochemical activity and it can be toxic to cells and cell organelles in the organism.

catalyase

H₂O₂ H₂O + 0₂

Hydrogen peroxide enzyme water oxygen

Substrates will only react with specific enzymes to form product. This is shown in Fischer’s lock and key theory and in Koshlands induced fit theory. Fischer’s lock and key theory implies that the enzyme is the lock and the substrate is the key. Only a

specific substrate (key) will fit into a specific lock (enzyme). Koshlands theory follows the same theme except that it prefers a more fluid idea. The enzyme is a glove and the substrate is a hand. The substrate and enzyme mould together for a perfect fit.

Hypothesis

I believe that as you increase the amount of enzyme the amount of product will also increase. This will happen at a proportionate rate so long as there is an excess amount of substrate (figure 1.1). This means that, for example, if I had ten enzymes each giving twenty products then twenty enzymes would give forty products, thirty enzymes would give sixty products. If there isn’t a continuous excess supply of substrate to the enzyme then the rate of product formation will rapidly decrease and then stop (figure 1.2).

Figure 1.1

The effect of rate of

product formation product

as enzyme concentration formation

increases. So long as

substrate amount is

kept in excess then

the rate will be proportionate.

Enzyme concentration

Figure 1.2

If substrate amount rate of x

is not kept in excess then product

product formation will stop formation

as soon as the immediate

substrate has been converted

to product. Enzyme concentration

X = the point where the substrate

runs out.

Product formation will continue at a proportionate rate when there is excess substrate as all the enzyme active sites are constantly occupied. The product formation rate suddenly drops off when substrate runs out leaving the active sites empty with no substrate to convert.

Apparatus

Figure 1.4

Shows the ...