Enzymes are biological molecules that catalyze chemical reactions and increase their rates. They are selective for specific substrates and only catalyze a few reactions. Enzymes work by lowering activation energy and can accelerate reactions by millions of times. They are not consumed in reactions and do not alter equilibrium. Enzyme activity is affected by factors like temperature, pH, inhibitors, and more. The lock and key and induced fit models describe how enzymes and substrates interact specifically in the active site. Cofactors like metal ions and coenzymes are required for some enzyme activity. Enzymes perform critical functions in cell signaling, movement, and metabolism and are targets of drugs and involved in diseases.

1. Enzymes
Dr. Muhammad Nabi
Doctor of Pharmacy,
M. Phil Biochemistry,
M. Phil Pharmacology,
Ph. D Pharmacology.

2. Enzymes
• Enzymes are biological molecules that catalyze
(i.e., increase the rates of) chemical reactions.
• In enzymatic reactions, substrates is
converted into products.
• Enzymes are selective for their substrates and
speed up only a few reactions from among
many possibilities.

4. Characteristics
• lowering the activation energy. As a result, products
are formed faster and reactions reach their equilibrium
state more rapidly.
• Most enzyme reaction rates are millions of times faster
than those of comparable un-catalyzed reactions.
• As with all catalysts, enzymes are not consumed by the
reactions they catalyze, nor do they alter the
equilibrium of these reactions.
• highly specific for their substrates.
• A few RNA molecules called ribozymes also catalyze
reactions

5. • Inhibitors: decrease enzyme activity;
• activators are molecules that increase activity.
• Many drugs and poisons are enzyme
inhibitors.
• Activity is also affected by temperature,
pressure, chemical environment (e.g., pH),
and the concentration of substrate.

6. • Enzymes are in general globular proteins and
range from just 62 amino acid residues in size,
to over 2,500 residues
• A small number of RNA-based biological
catalysts exist, with the most common being
the ribosome; these are referred to as either
RNA-enzymes or ribozymes.

7. • only a small portion of the enzyme (around 2–
4 amino acids) is directly involved in catalysis.
• The region that contains these catalytic
residues, binds the substrate, and then carries
out the reaction is known as the active site.
• Enzymes can also contain sites that bind
cofactors, which are needed for catalysis.

8. • Enzymes are long, linear chains of amino acids
that fold to produce a three-dimensional product.
• Individual protein chains may sometimes group
together to form a protein complex.
• Most enzymes can be denatured—that is,
unfolded and inactivated—by heating or chemical
denaturants, which disrupt the three-dimensional
structure of the protein.
• Depending on the enzyme, denaturation may be
reversible or irreversible.

9. Lock and key model
• Enzymes are very specific,
• Nobel laureate organic chemist Emil Fischer in 1894
suggested
• both the enzyme and the substrate possess specific
complementary geometric shapes that fit exactly into
one another.
• However, while this model explains enzyme specificity,
it fails to explain the stabilization of the transition state
that enzymes achieve.

10. Induced fit model
• In 1958, Daniel Koshland suggested a modification to the lock and
key model:
• Since enzymes are rather flexible structures, the active site is
continuously reshaped by interactions with the substrate as the
substrate interacts with the enzyme.
• As a result, the substrate does not simply bind to a rigid active site;
the amino acid side-chains that make up the active site are molded
into the precise positions that enable the enzyme to perform its
catalytic function.
• In some cases, such as glycosidases, the substrate molecule also
changes shape slightly as it enters the active site

11. Allosteric sites
• Allosteric sites are sites other than active sites on the
enzyme that bind to molecules in the cellular environment.
• The sites form weak, noncovalent bonds with these
molecules, causing a change in the conformation of the
enzyme.
• This change in conformation translates to the active site,
which then affects the reaction rate of the enzyme.
• Allosteric interactions can both inhibit and activate
enzymes and are a common way that enzymes are
controlled in the body.

12. Cofactors
• Cofactors: Some enzymes require non-protein
molecules called cofactors to be bound for
activity
– inorganic (e.g., metal ions and iron-sulfur clusters)
– organic compounds (e.g., flavin and heme).
– prosthetic groups, which are tightly bound to an
enzyme
– coenzymes, which are released from the enzyme's
active site during the reaction. E.g. NADH, NADPH
and adenosine triphosphate

13. • Aponzymes: Enzymes that require a cofactor
but do not have one bound are called
apoenzymes or apoproteins.
• Holoenzymes: An apoenzyme together with its
cofactor(s) is called a holoenzyme (this is the
active form).

14. Biological function
• They are indispensable for signal transduction and cell regulation, often
via kinases and phosphatases.
• They also generate movement, with myosin hydrolyzing ATP to generate
muscle contraction
• moving cargo around the cell as part of the cytoskeleton.
• Other ATPases in the cell membrane are ion pumps involved in active
transport.
• Enzymes are also involved in more exotic functions, such as luciferase
generating light in fireflies.
• Viruses can also contain enzymes for infecting cells, such as the HIV
integrase and reverse transcriptase, or for viral release from cells, like the
influenza virus neuraminidase.
• amylases and proteases break down large molecules (starch or proteins,
respectively) into smaller ones, so they can be absorbed by the intestines.

15. • Several enzymes can work together in a specific order,
creating metabolic pathways.
• In a metabolic pathway, one enzyme takes the product
of another enzyme as a substrate.
• After the catalytic reaction, the product is then passed
on to another enzyme.
• Without enzymes, metabolism would neither progress
through the same steps nor be fast enough to serve the
needs of the cell.
• Indeed, a metabolic pathway such as glycolysis could
not exist independently of enzymes.

16. Factors affecting enzyme activity
• Concentration:
• Changing the concentration of a substance only affects the rate of
reaction if it is the limiting factor: that is, it the factor that
is stopping a reaction from preceding at a higher rate.
• If it is the limiting factor, increasing concentration will increase the
rate of reaction up to a point, after which any increase will not
affectthe rate of reaction. This is because it will no longer be
the limiting factor and another factor will
be limiting the maximum rate of reaction.
• As a reaction proceeds, the rate of reaction will decrease, since the
Substrate will get used up. The highest rate of reaction, known as
the Initial Reaction Rate is the maximum reaction rate for
an enzyme in an experimental situation.
http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=
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17. Substrate Concentration
• Increasing Substrate Concentration increases the rate of
reaction. This is because more substrate molecules will be
colliding with enzyme molecules, so more product will be
formed.
• However, after a certain concentration, any increase will have
no effect on the rate of reaction, since Substrate
Concentration will no longer be the limiting factor. The
enzymes will effectively become saturated, and will be
working at their maximum possible rate.
http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=
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18. Enzyme Concentration
• Increasing Enzyme Concentration will increase
the rate of reaction, as more enzymes will be
colliding with substrate molecules.
• However, this too will only have an effect up
to a certain concentration, where the Enzyme
Concentration is no longer the limiting factor.
http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=
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19. Temperature
• 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.
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http://alevelnotes.com/Factors-affecting-Enzyme-Activity/146?tree=
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20. pH
• Different enzymes have different Optimum pH values. This is the pH
value at which the bonds within them are influenced by H+ and OH-
Ions in such a way that the shape of their Active Site is the most
Complementary to the shape of their Substrate. At the Optimum
pH, the rate of reaction is at an optimum.
• Any change in pH above or below the Optimum will quickly cause a
decrease in the rate of reaction, since more of the enzyme
molecules will have Active Sites whose shapes are not (or at least
are less) Complementary to the shape of their Substrate.
• Small changes in pH above or below the Optimum do not cause a
permanent change to the enzyme, since the bonds can
be reformed. However, extreme changes in pH can cause enzymes
to Denature and permanently lose their function.
• Enzymes in different locations have different Optimum pH values
since their environmental conditions may be different.
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21. Types of Enzyme inhibitors
http://www.wiley.com/legacy/college/boyer/0470003790/animations/enzyme_inhibition/enzyme_inhibition.htm
November 18, 2015

22. http://www.wiley.com/legacy/college/boyer/0470003790/animations/enzyme_inhibition/enzyme_inhibi
tion.htm
November 18, 2015

23. Medical applications of enzymes
http://www1.lsbu.ac.uk/water/enztech/medical.html
November 18, 2015

24. Thank You