Enzymes are proteins that catalyze chemical reactions by lowering activation energy. They are not consumed in reactions and can catalyze numerous reaction cycles. Nearly all biological reactions require enzyme catalysis. Enzymes contain active sites that bind specific substrates. The binding forms an enzyme-substrate complex that undergoes reaction, producing products. Cofactors like vitamins and ions can bind enzymes and are required for catalytic activity. The active site is a pocket formed by spatially distant amino acids that binds substrates and performs catalysis. Enzymes are measured in units describing their catalytic activity rate.

1. Enzymes
Prepared by:
Shaikh shohidul islam
Faculty member
Biochemistry and molecular biology
Gono University

2. • Enzymes are proteins except some
small RNAs(ribozymes) that increase
the rate of reaction by lowering the
energy of activation without
themselves being changed in the
overall process.
Define enzymes
(Enzymes as Biological Catalysts)

3. Why Are Enzymes So Important?
Why are we
devoting two whole
lecture topic to a
enzyme?
Nearly all chemical
reactions in
biological cells need
enzymes to make
the reaction occur
fast enough to
support life.
Image: Jumping rope, Meagan E. Klein

4. 1. Almost all enzymes are proteins (With the
exception of a few catalytically active RNAs,
the ribozymes”.
2. Water soluble-nondialyzable-amphoteric
compounds .
3. Enzymes are active outside the cells (enzymes
are active outside the cells)
Contain active sites which binds the substrates
forming ES complex which is then converted to EP
and subsequently into product.

5. Properties of
enzymes……..
 6. Enzymes are highly effective biological
catalysts, commonly enhancing reaction rates
by a factor of 105 to 1017. E.g. each
Catalase enzyme molecule can break 40 millions
molecules of H2O2. Enzymes are highly specific
for their subtrates and catalyze only one type of
chemical reaction.
 They are not consumed during the reaction they
catalyze and remain unchanged chemically in the
overall process.

6. What are
enzymes?
Enzymes are
__________
(tertiary and
quaternary
structures).

7. • Cofactor:
– A cofactor is a non-protein chemical compound that is
bound (either tightly or loosely) to an enzyme and is
required for catalysis.
– Types of Cofactors:
• Coenzymes.
• Prosthetic groups.
Apoenzyme = enzyme (-) cofactor
Holoenzyme = enzyme (+) cofactor
Inorganic cofactors – essential ions
Organic cofactors – coenzymes
Important Terms

8. Functions of Coenzymes
• Coenzymes are small organic molecules that are
often required to prepare the active site for
proper substrate binding and/or participate in
catalysis
• Because they are not destroyed during the
reaction, coenzymes are only required in small
quantities

9. Water Soluble Vitamins
• Vitamins are organic molecules that are essential for
metabolism, but can not be biosynthesized; they must be
consumed in the diet
• Many coenzymes come from water-soluble vitamins
• Water soluble vitamins are not stored in the body, and so
should be consumed daily

10. • Enzyme molecules contain a special
pocket or cleft called the active
sites.
ACTIVE SITES

11. 2) The active site of the enzyme
• Enzymes bind substrates to their active site
and stabilize the transition state of the
reaction.
• The active site of the enzyme is the place
where the substrate binds and at which
catalysis occurs.
• The active site binds the substrate, forming
an enzyme-substrate(ES) complex.
Active site
Binding site
Catalytic site

12. Salient features of
active sites
1 . The existence of active site is due to the tertiary structure of protein
resulting in three dimensional native conformation.
2. The active site is made up of amino acids (known as catalytic
residues)which are far from each other in the linear sequence of
amino acids (primary structure of protein). For instance, t he enzyme
lysozyme has 129 amino acids. The active site is formed by the
contribution of amino acid residues numbered 3 5, 52, 62, 63 and
101.
3. Active sites are regarded as clefts or crevices or pockets occupying a
small region in a big enzyme molecule.

13. UNIT OF ENZYME
ACTIVITY
• 1 IU ( International unit) of enzyme is the amount of
enzyme required to convert 1 μmol substrate to 1 μmol
product per minute under optimum conditions and it is
expressed as 1 IU/ min .
• So 1 IU =1 μmol/min.
• 1 kat = 1 mol per second.