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‫بسم هللا الرحمن الرحيم‬
‫‪ 221‬كيح علم اإلنزيمات‬
‫أ‪ /‬أروى الخيـــــــــــــــــــاط‬
‫‪[email protected]‬‬
‫مبنى ‪ 8‬الدور ‪ 3‬مكتب‪704‬‬
‫يوم الثالثاء ‪3-11‬‬
Introduction
Enzymology
Beginning
story
Louis Pasteur
19th century
Wilhelm Kühne
In 1878
Eduard Buchner
In 1897
As early as the late 1700s and early 1800s, the digestion of
meat by stomach secretions and the conversion of starch to
sugars by plant extracts and saliva were known. However, the
mechanism by which this occurred had not been identified
In the 19th century, when studying the fermentation of sugar
to alcohol by yeast, Louis Pasteur came to the conclusion
that this fermentation was catalyzed by a vital force contained
within the yeast cells called "ferments", which were thought to
function only within living organisms. He wrote that "alcoholic
fermentation is an act correlated with the life and organization
of the yeast cells, not with the death or putrefaction of the
cells.
In 1878, German physiologist Wilhelm Kühne first used the
term enzyme, which comes from Greek ενζυμον, "in leaven",
to describe this process. The word enzyme was used later to
refer to nonliving substances such as pepsin, and the word
ferment was used to refer to chemical activity produced by
living organisms.
In 1897, Eduard Buchner began to study the ability of yeast
extracts that lacked any living yeast cells to ferment sugar. In a
series of experiments at the University of Berlin, he found
that the sugar was fermented even when there were no living
yeast cells in the mixture.
He named the enzyme that brought about the fermentation of
sucrose "zymase".
In 1907, he received the Nobel Prize in Chemistry "for his
biochemical research and his discovery of cell-free
fermentation".
Definition
Catalyst are the substance that accelerate chemical reaction
Organic catalyst (enzyme)
2 Mg,2 Cl-)
Inorganic catalyst(Zn,
Enzymes are proteins that catalyze (i.e., increase the rates of)
chemical reactions
 Nearly all known enzymes are proteins in nature with the exception of
certain RNA molecules can be effective biocatalysts too. These RNA
molecules have come to be known as ribozymes.
 synthesized by the living cells
In enzymatic reactions, the molecules at the beginning
of the process are called substrates(S), and the
enzyme converts them into different molecules, called
the products(P)
S
E
P+E
In Biochemistry
substrate is a molecule or substance upon which an enzyme
acts.
Products is a substance produced as a result of the reactions.
Note:
 Enzyme Catalyze the chemical reactions without consumed
 Enzyme catalyzed reactions are mostly reversible
HOW THE ENZYME BIND WITH THE SUBSTRATE?
The enzyme can bind with the substrate by specific pocket on
the enzyme known as active sites which define as small
groove or area on the surface of the enzyme into which the
substrate fits.
that involve the formation of an intermediate enzyme-substrate
complex
S+E
ES
enzyme-substrate complex
P+E
How the active site become fits to
substrate?
Models that explain the enzyme specific towards substrate:
Lock and key" model:
Enzymes are very specific, because both the enzyme and the substrate
possess specific complementary geometric shapes that fit exactly into one
another.
Induced fit model:
The hypothesis suggested a modification to the lock and key
model: since enzymes are rather flexible structures, the active
site is continually 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 which make up the active site are moulded
into the precise positions that enable the enzyme to perform
its catalytic function.
How the enzyme increase the rate
of reaction?
The enzyme accelerate the rate of reaction through
1.Decreasing energy of activation without change free energy
Activation energy ΔG:
difference in the energy
level of substrate or
product and transition
state
(i.e. ΔG =
rate of
the reaction)
How the enzyme increase the rate of
reaction?
Catalytic functional group of enzyme interact with functional
group of S by weak bounds to form E S complex which
causes release small amount of free energy, this energy that
result from ES interaction called binding energy, which the
enzyme used free energy to decrease activation energy
Turnover number:
Define as capable of combining enzyme with a given
Total number of substrate molecules per minute.
•This tells how many S molecules are converted to product
by each enzyme molecule.
•It tells us how fast an enzyme work or turnover S into P.
•The turnover number varies from enzyme to enzyme.
e.g.
for catalase:turnover number is 5 x 106
for α-amylase→it is 1.9 x 104
This indicates that catalase is ~ 250 times more active than
amylase