An investigation into how enzyme concentration (catalyse in a potato) affects the rate of reaction an enzyme catalysed reaction.

AS BIOLOGY COURSEWORK

Investigation into how enzymes concentration affects the rate of reaction

Aim:

Theory

Enzymes are biological catalysts that are composed of globular protein molecules. ‘A catalyst is a molecule which speeds up a chemical reaction, but remains unchanged at the end of the reaction.’ (Cambridge Biology 1 by Mary Jones.) As an enzyme is a globular protein the molecule is curled up so the non-polar R groups point away from surrounding water into the centre of the molecule. Catalase is an enzyme made up of protein molecules. A catalase speeds up a reaction from the substrate. Catalase is present in the majority of living things including carrot, liver and potato. Hydrogen has the chemical formula of H2O2. It is a colourless liquid used in rocket propellant, bleaching textiles and in the manufacture of other chemicals. Hydrogen peroxide is a toxic and the catalase decomposes it down into the non-toxic water and oxygen. This reaction is important to the cell where it occurs because hydrogen peroxide would poison and kill the cells.

The potato enzyme will force the hydrogen peroxide to decompose into water and oxygen. This is a natural process that occurs and will carry on reacting until the substrate runs out. The enzyme does not run out and the surface area of the potato is directly proportional to the amount of enzyme as enzyme is present in every cell of potato.

If a substrate finds an enzyme it will try to fix into it’s active site, this is called ‘complex’. If the enzyme does not fit, it cannot be broken down. When the enzyme fits into the substrate, a reaction will occur .The enzyme chemically rearranges the molecules, and breaks the substrate into small soluble products. If the experiment contains too much acid the Ph level will drop. Therefore the enzyme will denature.

Letts educational GCSE science classbook

Encarta 98 Encyclopaedia

For a chemical reaction to occur, the reacting particles must collide. There must also be enough energy involved in the collision to break the chemical bonds in the reacting molecules. If the energy transfer is not large enough the particles will just bounce off another. A collision that does have enough energy to result in a chemical reaction is referred to as an effective collision. This approach to reactions is called collision theory.

From Collins study and revision science GCSE

Factors that effect the rate of reaction are:

Substrate concentration
Enzyme concentration
Temperature
Pressure
Light

A Catalyst

Substrate concentration

A higher substrate concentration means there is a greater number of substrate molecules. Therefore, there is a ,higher probability that the molecules will collide and so the reaction will occur at a faster rate as explained in the collision theory. Although, if the enzyme is kept constant, there is a point where increasing the substrate concentration will not increase the rate of reaction as all the active sites will be in use. The extra molecules have to wait until an active site becomes available.

Enzyme concentration

There are more molecules present with a higher enzyme concentration. When there is a high enzyme concentration, there are more active sites available for substrate to bind with. This means there is a higher chance and more opportunities for a substrate colliding into an available active site. The more collisions with the active site, the faster the reaction as explained by the collision theory.

Surface Area

The larger the surface area, the more enzyme molecules are exposed and able to react and a greater possibility of collision. Therefore the larger the surface area exposed, the faster the reaction rate.

Ph Level

The majority of enzymes work most effectively at Ph 7. Substrate molecules fit into the enzyme’s active site because of the surface electrical charge of amino acids in the enzyme molecule and the charge of the substrate molecule. The enzyme’s substrate bonding will be affected if hydrogen (positive) or hydroxide (negative) Ions are present, as they can no longer bind. The enzyme’s optimum Ph level will be the Ph level which the amount of hydrogen and Hydroxide ions create to get the right balance of charges on the substrate molecules, and at the active site.

Temperature

At a high temperature there is a lot more energy so the molecules move fast and the molecules have more opportunities to collide and react.

Thus as the molecules move faster the collisions occur at a faster rate. However if the temperature is increased too much the collision becomes too energetic and the bonds between the active site begin to break. This means the enzyme has become denatured so the substrate cannot fit into the enzyme’s active site, to react. The optimum temperature for an enzyme is usually approximately 40oC, catalase’s optimum temperature is 37oC. This ...