the effect of catalase concentration on the breakdown rate of h2o2

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enzyme coursework:

the effect of catalase concentrations on the rate of

break down of hydrogen peroxide

sara de sousa

scientific knowledge and understanding:

A rate is a measure of change that occurs in a given time whilst a reaction is the interaction of substances undergoing chemical change.

The velocity at which any mix of substances are transformed into a product/s in a given unit of time is the rate of reaction. The speed at which this modification occurs relies on two main factors; the amount of collisions between reacting particles and what portion of these collisions are successful in producing a change within the substances present.

Reactions between chemical substances will only occur if the particles collide with enough energy to break their initial bonds. This initial energy is called the activation energy.

Collision theory: In order to react, particles must collide with a force sufficient to overcome the activation energy.

There are four methods of increasing the rate of a reaction, and all can be explained in terms of increasing the number of collisions between reacting particles;

  1. Temperature: when the temperature is increased particles move faster as they have more kinetic energy, encouraged by the heat. The more rapidly particles are moving, the more collisions are going to occur.
  2. Pressure (or concentration): the more concentrated a solution, the more particles of a reactant are present. The higher the number of particles present the higher the likelihood of collisions.
  3. Surface area: if one of the reactants is a solid then breaking it up into smaller pieces will increase its surface area. This means that particles in the solution around it will have a larger area to work on, so there will be more collisions in a shorter time. If both reactants are dissolved in solution/in a liquid state, surface area does not pertain and they relate directly to pressure/concentration.
  4. Catalysts: catalysts work by giving the reacting particles a surface to stick to, where they can bump into each other. A catalyst can also lower the activation energy of particles. This will obviously increase the number of successful collisions.

An enzyme is a protein that acts as a biological catalyst, speeding up the rate at which a biochemical reaction takes place, without altering the nature of the reaction and remaining unchanged at the end.

Enzymes that work in solutions are globular proteins. The molecules are coiled up into a precise 3-dimensional shape, with the hydrophilic R groups placed on the outside and the hydrophobic R groups placed on the inside of the structure making them water-soluble. These R groups are held in place by hydrogen, ionic and disulphide bonds, as well as hydrophobic interactions that occur between the non-polar parts of the molecule.

The reaction of changing substrate into products takes place at the ‘active site’ of the enzyme molecule. This is a small depression in the surface of the enzyme that has a clear-cut defined shape which only one specific type of substrate molecule can fit into, perfectly, meaning that a given enzyme is only able to catalyse a single chemical reaction. When the substrate molecules crash into the enzymes’ active site, the R groups of the amino acids, which line the surface of the active site, form temporary bonds with the substrate, creating a momentary enzyme-substrate complex. Whilst in this complex, bonds are either broken down, in a single substrate molecule, or urged to synthesise, between two substrate molecules. After this change has occurred the product/s renounce the active site, leaving the enzyme molecule unchanged, ready to be made use of again.

The following equation is representational of the progress of an enzyme-catalysed reaction;

                                   E + S ↔ ES ↔ EP ↔ E + P

E = enzyme        

S = substrate              

ES = enzyme-substrate complex  

EP = enzyme-product complex

P = product

The number of substrate molecules that a single enzyme molecule can catalyse in a given period of time is called the turnover number.

Enzymes are essential for everyday life. Without them, all biochemical reactions would take place far too slowly to maintain any life at all.

Carbonic anhydrase, for example, is found in red blood cells. It catalyses the reaction between carbon dioxide and water which leads to the formation of hydrogen carbonate ions, which are very important in the transport of CO2 by the blood.

Another example is hydrogen peroxide, H2O2, which breaks down into water and oxygen. It is a powerful oxidising agent produced in the body, as a by-product of fatty acid and cholesterol oxidation, and is produced by white blood cells to kill bacteria.

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In plants hydrogen peroxide is produced during an intermediate stage of nitrogen fixation.

Regardless of whether it is produced in plants or animals, it needs to be detoxified rapidly before it causes any damage to cells.

A single catalase (enzyme) molecule can break down 5.6 million molecules of hydrogen peroxide in one minute. It is therefore not very surprising that catalase is found in high concentrations in cells.

Enzymes are also a principal mechanism in many industrial processes. They are key in the production of vinegar, yoghurt and cheese, in brewing, washing powders, processing of leather, etc. ...

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