Enzymes are protein molecules that act as catalysts for chemical reactions in living organisms. They speed up reactions by lowering their activation energy but are not used up in the process. Enzymes have specific active sites that substrates bind to, and use lock-and-key or induced-fit mechanisms to catalyze reactions. The rate of enzymatic reactions depends on substrate concentration according to Michaelis-Menten kinetics, characterized by the parameters Km and Vmax. Enzymes are essential for many biological functions and processes and have important industrial applications like food production, biofuels, and cleaning products.

1. Prepared By:
 Mariam rafiq malik
The Biocatalysts
EnzymesCourse : Biochemistry – 1
Course Incharge : Dr. Suad Naheed

2. Enzymesare protein moleculesin cells which work as catalysts. Enzymes speedup chemical
reactionsin the body, but do not get used up in the process.
 Almost all biochemical reactions in living things need enzymes. With an enzyme, chemical reactions
go much faster than they would without the enzyme. The substancesat the start of the reaction are
called substrates. The substances at the end of the reaction are the products. Enzymes work on the substrates,
and turn them into products.
 The first enzyme was found in 1833, by Anselme Payen.
Introduction

3. Enzymesare large molecules made from
many amino acids.
 The amino acids link together in a long chain,
which is folded up into a complex structure.
Enzymes have a part which holds the substrate:a
"claw, cleft, hollow or knob to grasp,
hold, stretchand bend the molecule it acts on,
the substrate"

4. There are thousands of different enzymes. Enzymes have names which show what they do.
Enzyme names usually end in –aseto show that they are enzymes. Examples of this include ATP
synthase.
 It makes a chemical called ATP. Another example is DNA polymerase. It reads an intact DNA strand
and uses it as a template to make a new strand.
One example of an enzyme is amylase, found in saliva. It breaks down starchmolecules into
smaller glucoseand maltose molecules. Another kind of enzyme is lipase. It breaks
down fatsinto smaller molecules.
The proteasesare a whole class of enzymes. They break down other enzymes and proteins back into
amino acids. Nucleasesare enzymes that cut DNA or RNA, often in specific place in the molecule.

5.  Enzymes are not only for breakinglarge chemicalsinto smaller chemicals. Other enzymes take smaller chemicalsand build them up into bigger
chemicals, and do many other chemical tasks.
 Most enzymes will not work unless the temperatureand pHare just right. In mammals the right temperature is usuallyabout 37oC
degrees(body temperature).
 The correct pH can vary greatly. Pepsin is an example of an enzyme that works best when pH is about 1.5.
 Heating an enzyme above a certaintemperature will destroy the enzyme permanently.It will be broken down by protease and the chemicals will
be used again.

6. Some chemicals can help an
enzyme do its job even better.
These are called activators.
Sometimes, a chemical can slow
down an enzyme or even make the
enzyme not work at all. These are
called inhibitors. Most drugs
are chemicals that either speed up
or slow down some enzyme in the
human body.

7. Enzymes are able to do various and numerous jobs, which can be roughly sorted into two
types: biological functions and industrial applications. On the biological aspect, enzymes
are instrumental substances to many functions in living organisms.
They can move parts of a cell’s internal structure and reorganize them to regulate cell
activities. They deliver packages from one part to another inside cells. They pull
chromosomes apart when the cells undergo mitosis. They pull cilia to trigger cell
movement or to help cells move mucus up your airway as a routine to keep the airway
clear. Common enzymes involved in these movement mentioned above are myosin
ATPase, kinesin ATPase, and dynein ATPase.
Functions

8. They can generate energy for living
organisms. Adenosine triphosphate, also
known as ATP, is the main storage form of
chemical energy. ATP is a charged battery
that can release energy that powers
biological activities. Enzymes are the
transformer to turn energy into proper
chemical forms and store it in ATP
molecules. Most of these enzymes are called
ATP synthases, which act as ion pumps
through passive transport mechanisms.

9. Many nutritional ingredients are in the form of
large molecules such as sugar, proteins, and fat,
which cannot be up taken easily by human body.
Hence, these ingredients are broken down by
enzymes into smaller pieces before absorption,
and this process is called catabolism.

10. In addition, enzymes are the important players in many other
functions, including immune responses, hormone and neural
signal transduction and regulation, and aging processes.

11. Beer brewing. Many enzymes are involved in
production in a brewery. These enzymes work in a
chain or synergy to give the correct levels of
alcohols and carbohydrates for the best quality and
flavor. The list is long but not exhaustive: amylases,
glucanases, proteases, beta glucanases,
arabinoxylans, amyloglucosidases, and acetolactate
decarboxylases.
Food processing.Amylases from fungi and
plants are used in the production of sugars from
starch in making corn syrup. Catalytic enzymes
are used in breaking down raw plant tissues into
dietary fibers, removing lactose from milk for
lactose-intolerant consumers, and in the baking
process when yeast raises the dough.
Applications

12. Dairy industry. Amylases, proteases, and lipases are often used to treat milk.
These enzyme pre-digest carbohydrates, proteins, and fats before human
consumption, so that our bodies absorbthese nutrition conveniently. Lipases are
also used in ripening blue-mold cheese, and some other enzymes could be used to
kill the bacteria in the milk.
Meat tenderizing. As a modern culinary art, papain is often
used to soften meats before cooking, which give a tender and
smooth texture of the final dishes.

13. Paper industry. Enzymes
like amylases, xylanases, and
cellulases can lower the
viscosity of pulp and remove
lignin in order to soften and
brighten paper.
Biofuel industry. Enzymes, such as
cellulases, can assist the conversion of biomass to
cellulosic ethanol, which is then used in
automobile gasoline. Some esterases are also
used to convert natural plant oils into
hydrocarbons that can be used as or blended in
fuels to reduce carbon emission.

14. Cleaning industry. Proteases, amylases, lipases and
cellulasesare often used in cleaning products, such as laundry
detergents and dish soaps to assist removal of protein, oil, and
greasy stains. They can also act as fabric conditioners.
Rubber industry. Catalase enzymes can convert
latex into foam rubber.

15. Molecular biology. DNA ligase and polymerases
are now widely used in genetic engineering, pharmaceutical,
structural biology, and also play an important role in forensic
sciences.

16. Class 1. Oxidoreductases.
To this class belong all enzymes catalysing oxidoreduction reactions. The substrate that is oxidized is
regarded as hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The
common name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be
used. Oxidase is only used in cases where O2 is the acceptor.
Class 2. Transferases.
Transferases are enzymes transferring a group, e.g. a methyl group or a glycosyl group, from one compound (generally
regarded as donor) to another compound (generally regarded as acceptor). The systematic names are formed according to the
scheme donor:acceptor grouptransferase.
The common names are normally formed according to acceptor grouptransferase or donor grouptransferase. In many cases,
the donor is a cofactor (coenzyme) charged with the group to be transferred.
Classes

17. Class 3. Hydrolases.
These enzymes catalyse the hydrolytic cleavage of C-O, C-N, C-C and some other bonds, including
phosphoric anhydride bonds.
Although the systematic name always includes hydrolase, the common name is, in many cases,
formed by the name of the substrate with the suffix -ase. It is understood that the name of the
substrate with this suffix means a hydrolytic enzyme.
Class 4. Lyases.
Lyases are enzymes cleaving C-C, C-O, C-N, and other bonds by elimination, leaving
double bonds or rings, or conversely adding groups to double bonds. The systematic name is
formed according to the pattern substrate group-lyase.

18.  The basic mechanism by which enzymes catalyze
chemical reactions begins with the binding of
the substrate (or substrates) to the active site on the
enzyme.
 The active site is the specific region of the enzyme
which combines with the substrate. The binding of the
substrate to the enzyme causes changes in the
distribution of electrons in the chemical bonds.
 The products are released from the enzyme surface to
regenerate the enzyme for another reaction cycle.
 The active site has a unique geometric shape that is
complementary to the geometric shape of a substrate
molecule, similar to the fit of puzzle pieces. This means
that enzymes specifically react with only one or a very
few similar compounds.
Mechanism

19. Lock and Key Theory:
 The specific action of an enzyme with a
single substrate can be explained using
a Lock and Key analogy first postulated in
1894 by Emil Fischer. In this analogy, the
lock is the enzyme and the key is the
substrate. Only the correctly sized key
(substrate) fits into the key hole (active
site) of the lock (enzyme).
 Smaller keys, larger keys, or incorrectly
positioned teeth on keys (incorrectly
shaped or sized substrate molecules) do
not fit into the lock (enzyme). Only the
correctly shaped key opens a particular
lock. This is illustrated in graphic on the
left.

20. Induced Fit Theory:
 Not all experimental evidence can be
adequately explained by using the so-
called rigid enzyme model assumed by
the lock and key theory. For this reason,
a modification called the induced-fit
theory has been proposed.
 The induced-fit theory assumes that the
substrate plays a role in determining the
final shape of the enzyme and that the
enzyme is partially flexible.
 This explains why certain compounds
can bind to the enzyme but do not react
because the enzyme has been distorted
too much.

21. The effect of substrate concentration on
enzyme activity
A simple chemical reaction with a single substrate shows a linear
relationship between the rate of formation of product and the
concentration of substrate, as shown below:
Km + Vmax

22. For an enzyme-catalysed reaction, there is usually a hyperbolic relationship between the
rate of reaction and the concentration of substrate, as shown below:
• At low concentration of substrate, there is a steep increase
in the rate of reaction with increasing substrate
concentration.
• The catalytic site of the enzyme is empty, waiting for
substrate to bind, for much of the time, and the rate at
which product can be formed is limited by the
concentration of substrate which is available.
• As the concentration of substrate increases, the enzyme
becomes saturated with substrate. As soon as the catalytic
site is empty, more substrate is available to bind and
undergo reaction.
• The rate of formation of product now depends on the
activity of the enzyme itself, and adding more substrate
will not affect the rate of the reaction to any significant
effect.

23. The rate of reaction when the enzyme is saturated
with substrate is the maximum rate of
reaction, Vmax.
The relationship between rate of reaction and
concentration of substrate depends on the affinity
of the enzyme for its substrate. This is usually
expressed as the Km (Michaelis constant) of the
enzyme, an inverse measure of affinity.
For practical purposes, Km is the
concentration of substrate which
permits the enzyme to achieve half
Vmax.
An enzyme with a high Km has a low affinity for its
substrate, and requires a greater concentration of
substrate to achieve Vmax."

24. The importance of determining Km and Vmax
The Km of an enzyme, relative to the concentration of its substrate under normal conditions permits prediction of
whether or not the rate of formation of product will be affected by the availability of substrate.
An enzyme with a low Km relative to the physiological
concentration of substrate, as shown above, is normally
saturated with substrate, and will act at a more or less
constant rate, regardless of variations in the
concentration of substrate within the physiological
range.

25. An enzyme with a high Km relative
to the physiological concentration of
substrate, as shown above, is not
normally saturated with substrate,
and its activity will vary as the
concentration of substrate varies, so
that the rate of formation of product
will depend on the availability of
substrate.
If two enzymes, in different
pathways, compete for the
same substrate, then knowing
the values of Km and Vmax for
both enzymes permits
prediction of the metabolic fate
of the substrate and the relative
amount that will flow through
each pathway under various
conditions.

26. THANKYOU
REFRENCES:
 http://www.sbcs.qmul.ac.uk/iubmb/enzyme/rules.html
 https://www.creative-
enzymes.com/resource/enzymes-functions_2.html
 http://www.biotopics.co.uk/other/enzyme.html
 https://www.ucl.ac.uk/~ucbcdab/enzass/substrate.htm