Project Report on Enzymes
- Almost all enzymes are proteins that catalyze the biochemical reactions in the living cells, hence called biocatalyst.
- Enzymes are proteinaceous in nature (summer 1926) with the exception of recently discovered two RNA enzymes:-
i. Ribozyme : cech et al , 1981 isolated ribozyme from Tetrahymena.
ii. Ribonuclease-P : discovered by Altman from bacteria.
- An enzyme like any other protein has secondary and tertiary structure. In the tertiary structure the backbone of protein chain folds upon itself, the chain crosses itself and many crevices or pockets are made. One such pocket is the active site.
- An active site of an enzyme is a cervices or pocket into which the substrate fits. A substrate is a specific compound acted upon by an enzyme. Thus enzymes through their active site catalyse reaction at a high rate.
- Enzymes are Organic catalysts, they are Inorganic catalyst also which do not occur in living cells.
- Enzymes isolated from thermophillic organisms who normally live under extremely high temperatures (e.g. hot vents and sulphur springs) are thermally stable and retain their catalatic power even at high temperatures (above 80-90C).Thus thermal stability is an important quality of such isolated from thermophilic organisms.
| Enzymes | Inorganic catalyst |
| Almost all enzymes are proteins and have a
complex molecular organization.
They occur in living cells An enzyme catalyses only a specific reactions They get damaged at high temperatures (above 40C) They are highly efficient |
They are usually small and simple molecules
like nickel, platinum etc.
They do not occur in living cells They are not specific for any one reaction and can catalyse a number of reactions They work efficiently at high temperatures and pressures. They are less efficient. |
Nature of Enzyme Action:
Each enzyme has an active site to which the substrate binds and forms a short lived highly reactive enzyme substrate complex. This is followed by formation of the enzyme-product complex (EP). Finally the enzyme product complex dissociates into the product (P) and the enzyme freed remains unchanged and is able to bid to more substrate molecules.
The formation of ES complex is essential for catalysis.
The catalytic cycle of an enzyme action can be described as follows:
- The substrate binds to the active site of the enzyme.
- The binding of the substrate induces the enzyme to alter the shape and fit more tightly around the substrate.
- The active site of the enzyme which is in close proximity of the substrate breaks the chemical bonds of the substrate and an enzyme-product complex is formed.
- The enzyme releases the product(s) of the reaction and the free enzyme is ready to take up another molecule of the substrate.
Factors affecting Enzyme Activity
- The activity of an Enzyme is affected by its environmental conditions. Changing these alter the rate of reaction caused by the enzyme. In nature, organisms adjust the conditions of their enzymes to produce an optimum rate of reaction, where necessary, or they may have enzymes which are adapted to function well in extreme conditions where they live.
Temperature
- Increasing temperature increases the Kinetic Energy that molecules possess. In a fluid, this means that there are more random collisions between molecules per unit time.
- Since enzymes catalyse reactions by randomly colliding with Substrate molecules, increasing temperature increases the rate of reaction, forming more product.
- However, increasing temperature also increases the Vibrational Energy that molecules have, specifically in this case enzyme molecules, which puts strain on the bonds that hold them together.
- As temperature increases, more bonds, especially the weaker Hydrogen and Ionic bonds, will break as a result of this strain. Breaking bonds within the enzyme will cause the Active Site to change shape.
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This change in shape means that the Active Site is less Complementary to the shape of the Substrate, so that it is less likely to catalyze the reaction. Eventually, the enzyme will become Denatured and will no longer function.
- As temperature increases, more enzymes' molecules' Active Sites' shapes will be less Complementary to the shape of their Substrate, and more enzymes will be Denatured. This will decrease the rate of reaction.
- In summary, as temperature increases, initially the rate of reaction will increase, because of increased Kinetic Energy. However, the effect of bond breaking will become greater and greater, and the rate of reaction will begin to decrease.
- The temperature at which the maximum rate of reaction occurs is called the enzyme's Optimum Temperature. This is different for different enzymes. Most enzymes in the human body have an Optimum Temperature of around 37.0 °C.
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