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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
|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
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
- 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.
- 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
- 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.
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
- 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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