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Nature of Enzymes
Roll #: 0101-MSBOT-201423
Proteins that function as biological catalysts are
Enzymes speed up specific metabolic reactions.
Low contamination, low temperature and fast
metabolism are only possible with enzymes.
Metabolism is fast, with the product made to a high
degree of purity.
They have molecular weights ranging from 10,000 to
Reversible - can catalyse the reaction in both
Denatured by high temperature and change in pH
Rate of action affected by temperature and pH
Protein Nature of Enzymes
Composed of C, H, O and N. Sulphur (S) may also
One or more polypeptide chains - large number of
linked amino acids.
Formed on the ribosome (70s, 80s) – translation of
mRNA during protein synthesis.
Denatured by high temperature and unfavourable
Many enzymes require the presence of other
compounds - cofactors - before their catalytic
activity can be exerted.
This entire active complex is referred to as the
holoenzyme; i.e., apoenzyme (protein portion) plus
the cofactor (coenzyme, prosthetic group or metal-
ionactivator) is called the holoenzyme.
Apoenzyme + Cofactor = Holoenzyme
According to Holum, the cofactor may be:
1. A coenzyme - a non-protein organic substance
which is dialyzable, thermostable and loosely
attached to the protein part.
2. A prosthetic group - an organic substance which is
dialyzable and thermostable which is firmly
attached to the protein or apoenzyme portion.
3. A metal-ion-activator - these include K+, Fe++,
Fe+++, Cu++, Co++, Zn++, Mn++, Mg++, Ca++,
Folded Shape of Enzymes
The polypeptide chains are folded into a particular
three-dimensional shape (H-bonds).
The correct folded shape is essential for enzyme
action ‘tertiary structure’.
The shape gives the enzyme special areas known as
The compatible substrate molecules bind to the
complementary active site.
Different enzymes have a differently shaped active
Role of Enzymes in Living Things:
Enzymes catalyse all metabolic reactions.
They lower the activation energy – the energy
input needed to bring about the reaction.
Regulate the thousands of different metabolic
reactions in a cell and in the organism.
The activity of a cell is determined by which
enzymes are active in the cell at that time.
Cell activity is altered by removing specific enzymes
and/or synthesising new enzymes.
Specificity of Enzymes
One of the properties of enzymes that makes them so important as
diagnostic and research tools is the specificity they exhibit
relative to the reactions they catalyze. A few enzymes exhibit
absolute specificity; that is, they will catalyze only one
particular reaction. Other enzymes will be specific for a
particular type of chemical bond or functional group. In
general, there are four distinct types of specificity:
1. Absolute specificity - the enzyme will catalyze only one
2. Group specificity - the enzyme will act only on molecules
that have specific functional groups, such as amino,
phosphate and methyl groups.
3. Linkage specificity - the enzyme will act on
a particular type of chemical bond regardless
of the rest of the molecular structure.
4. Stereochemical specificity - the enzyme
will act on a particular steric or optical
isomer. Though enzymes exhibit great degrees
of specificity, cofactors may serve many
Active Site Theory
“Lock and Key Hypothesis and Induced Fit”
The enzyme’s active site has a shape complementary
to the substrate.
The substrate locks into the active site of the enzyme.
The active site alters its shape holding the substrate
more tightly and straining it.
An enzyme-substrate complex is formed.
The substrate undergoes a chemical change – a new
substance (product) is formed.
The product is released from the active site.
The free unaltered active site is ready to receive fresh
Industrial Uses of Enzymes
Bio processing is the use of biological materials
(organisms, cells, organelles, enzymes) to carry out
manufacturing or treatment procedures of commercial
or scientific interest.
Glucose isomerase: production of fructose from
Sucrase: production of glucose and fructose from
sucrose (much sweeter).
Glucose oxidase: testing of blood/urine for glucose
Pectinase: production of clear juice from
apples/grapes etc for cider/wine-making .