Experiment to study the effect of Changing enzyme concentration on the rate of catalase action.

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Background

A definition of an enzyme is a biological catalysts; proteins made by living organisms, which speed up a chemical reaction. Catalysts enable substances to react more easily.   They do this by helping bonds break between atoms to break and form more easily. The particles need less energy to react, so the reactions proceed more quickly.

Enzymes are biological catalysts this means that they speed up reactions that would normally occur quite slowly. Enzymes are used to break down substances and are used in many metabolic processes such as digestion. Chemical reaction takes place all the time in living organisms and the enzymes that are present in the cells make the reaction occur much more quickly.

 

Chemical reactions involve one substance changing into another. The substance that is begun with is called a substrate and the substance made by the reaction is called a product. Enzymes change their substrate to products:

e.g:

Enzymes are made up of protein, and have a precise 3D shape. On there surface is an active site or a dent, which is of a very specific shape. It is exactly the rite size and shape for a molecule of the enzymes substrate to fit into.  Each enzyme has its own shape or active site, which will only fit together with its own substrate (chemical).

When the substrate molecule fits into the active site the enzyme ‘tweaks’ the substrate molecule making it out of shape and so breaking it into product molecules. These products leave their active site, which are ready to do the same thing to another substrate molecule.

The lock and key process

More enzyme therefore greater activity because there are more active sites.

The substrate we are studying is hydrogen peroxide and its enzyme catalase.

Catalase is found in all living cells. It is essential to be there because hydrogen peroxide is a poison and a very dangerous substance, which is produced during chemical reactions and therefore needs to be destroyed quickly. The catalase reacts with the hydrogen peroxide and breaks it down to produce water and oxygen.

Catalase + hydrogen peroxide                   water + oxygen

More catalse is produced by more surface area – explain.

ADD- used for respiration, look up shape of catalase and hydrogen peroxide.

SURFACE AREA! HOW IT WILL EFFECT THE RATE OF CATALYSE ACTION and enzyme concentration.

Surface area – show diagram of cut chips.

Characteristics of enzymes:

  • Enzymes are proteins - they have a precise 3D shape with an active site.
  • They are specific and only work on one substrate – each enzyme can only ‘tweak’ one kind of substrate into one kind of product.
  • Catalysts – they are unchanged by the reaction that they catalyse and they can be used over and over again.
  • Effected by temperature – because they are proteins they are effected by temperatures above 40ºC
  • Effected by Ph  - they only work best at there optimum Ph, this is because they are proteins and damaged by very acidic or alkaline conditions.
  • The more enzymes the faster the rate of reactions

Factors that may effect the rate of reaction.

Temperature

As temperature increases, reactions will occur faster because the molecules move faster, they bump into one another and react more often. (Kinetic theory). In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured. This usually happens when the temperature rises above 50 / 60ºc. Usually a rise of 10ºc, doubles the rate of reaction. Enzymes work at there best at the temperature of 40ºc. To control this variable, the temperature should be maintained at a fairly constant level that allowed the enzyme to work effectively.

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pH

Any change in pH affects the ionic and hydrogen bonding in an enzyme and so alters it shape. Not all enzymes work best in the same pH, each enzyme has an optimum pH at which its active site best fits the substrate and at which it is working at its fastest rate. For example amylase works best or has and optimum pH of about 8, but stomach protease (pepsin) has an optimum pH of about 4/5. Variation at either side of the enzyme, of pH results in denaturation of the enzyme and a slower rate of reaction.

Proteins ...

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