INTRODUCTION MECHANISM FACTORS CATALYSIS COVALENT CATALYSIS ACID BASE CATALYSIS pH EFFECT

1. TRINITY INSTITUTE OF MANAGEMENT &
TECHNOLOGY
( Affiliated to IKG Punjab Technical University )
CHURCH NAGAR, GURU GOBIND SINGH AVNUE,
CHOGITTI, JALANDHAR, PUNJAB – 144009
SUBMITTED BY SUBMITTED TO
Ms. Shamma Fatima Prof. Amandeep Paul

2. INTRODUCTION OF ENZYMES
Enzymes are proteins produced by living cells. They are
biocatalysts i.e., they are able in very small amount to
modify chemical reactions. Enzymes are very useful
tools in the diagnostics of diseases. Enzymes are specific
in their reactions. Enzymes increase reaction rate by
lowering its activation energy. Some enzymes can make
there conversion of substrate to product occur many
million of time faster. Most enzymes are proteins.
Simple enzymes composed of whole proteins. Complex
enzymes composed of protein plus relatively small
organic molecules.

3. Enzymes are biological catalysts (also known as
biocatalysts) that speed up biochemical reactions in
living organisms. They can also be extracted from cells
and then used to catalysed a wide range of
commercially important processes. For example, they
have important roles in the production of sweetening
agents and the modification of antibiotics, they are used
in washing powders and various cleaning products. The
word ‘enzyme’ was first used by the German
physiologist Wilhelm Kuhn in 1878, when he was
describing the ability of yeast to produce alcohol from
sugars, and it is derived from the Greek words enzymes
(meaning ‘within’) and zyme (meaning ‘yeast).

4. ENZYMES ACTION – can occur ways :-
1. Lock and Key model – The substrate molecule
has a specific 3-dimensional shape that allows it
to active site. Both enzyme and substrate already
exist in these specific 3-dimensional shapes.
2. Induced fit model – An interaction between the
enzyme and substrate induces or changes the
shape of the molecules to produce a suitable fit.

6. Catalysis :- Amino acid side chains that can donate
or accept protons can participate in chemical reactions as
acid base catalysis.
In metal ion catalysis, the unique electronic properties of
the metal ions facilities the reaction.
Important factor in enzyme catalysis include general acid
& base catalysis, orbital steering , entropic restriction
orientation effects.
Types of catalytic mechanism of enzymes:-
1. Acid – base catalysis.
2. Covalent catalysis.
3.Metal ion catalysis.
4. Electronic catalysis.
5.Proximity and orientation effect.

7. Covalent catalysis :-
 In an enzymatic reaction, covalent catalysis occurs
when the substrate become temporarily covalently
attached to the enzyme during the catalytic reaction.
 In this reaction, the enzyme contains a reactive group,
usually a nucleophilic residue or an electrophilic
residue, which reacts with the substrate through a
nucleophilic or electrophilic attack.
 The nucleophilic groups can be either RCOO-, RNH,
ROH that are present on the side-chains of amino acid
residues, Enzyme molecules are poor in electrophilic
groups, but electrophilic catalysis does occur with those
enzymes that contain metals or prosthetic groups that
act as electron sinks during catalysis.

8.  At a later stage in covalent catalysis, the covalent
bond must be broken to regenerate the enzyme.
 This mechanism is utilized by the catalytic triad of
enzymes such as proteases like chymotrypsin and
trypsin, where an acyl-enzyme intermediate is
formed.
Chymotrypsin is a degradative protease of the
digestive system.
It catalyzes the cleavage of peptide bonds that are
adjacent to large aromatic.
It cleaves the peptide bond on the carboxyl
terminus side of the protein.

9. Acid base catalysis:-
 acid catalysis and base catalysis, a chemical
reaction is catalyzed by and acid or a base.
 the acid is the proton donor and the base is the
proton acceptor.
Typical reactions catalyzed by proton transfer
are esterfications and aldol reactions.
 In these reactions, the conjugate acid of
the carbonyl group is a better electrophile than the
neutral carbonyl group itself.
 Depending on the chemical species that act as the
acid or base, catalytic mechanisms can be classified as
either specific catalysis and general catalysis.
Many enzymes operate by specific catalysis.

10. Types of acid base catalysis:-
General acid-base catalysis is involved in a majority of
enzymatic reactions, wherein the side chains of various
amino acids act as general acids or general basis.
General acid–base catalysis needs to be distinguished
from specific acid–base catalysis.
 Specific acid-base catalysis means specifically -OH or
H+accelerates the reaction.
The reaction rate is dependent on pH only (which of
course is a function of-OH and H+ concentrations) and
not on buffer concentration.
 In General acid-base catalysis, the buffer aids in
stabilizing the transition state via donation or removal
of a proton.
The rate of the reaction is dependent on the buffer
concentration.

11. pH effect:-
Many acid-base catalysis reactions involve histidine
because it has a pKa close to 7, allowing it to act as
both an acid and a base.
The great majority of enzyme reactions–the
chemical reactions on which life depends–take place
in water, under “physiological” conditions, near pH 7.