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Biochem
1. B.7.4 DETERMINE VMAX AND THE VALUE
OF THE MICHAELIS CONSTANT (KM ) BY
GRAPHICAL MEANS AND EXPLAIN ITS
SIGNIFICANCE.
2. The following can be deduced from the graph:
•At low substrate concentration, the rate of the reaction is proportional to
the substrate concentration; enzyme is available to bind to the substrate.
•As the substrate concentration is increased, the rate decreases and is no
longer proportional to the substrate concentration; some of the enzyme
active sites are occupied by substrate and is not available
•At high substrate concentration, the rate is constant and independent of
substrate concentration; at this point the enzyme is saturated with
substrate.
3.
4. Michaelis-
Menten equation
Two features of Michaelis-Menten kinetics
to note:
6. • Definition :Maximum velocity of enzyme under the
condition of the experiment
•Has the unit of rate.
•Varies from one enzyme to another and with PH,
temperature
•The rate of reaction is sometimes expressed as the
turnover number: the number of molecules of substrate
that can be processed into products per enzyme molecule
per unit time
•E.g : the enzyme catalase is a very fast enzyme with
turnover rate of up
to 100000 molecules of its substrate H2O2 per second
8. •Definition: the substrate concentration at which the
reaction rate is equal to one half its maximum value.
•Has the unit of concentration
•Varies with PH and temperature
•The value of Km gives info about affinity of enzyme for its
substrate.
•A low value of Km that the reaction is going quickly even at
low substrate concentrations.
•A higher value means that the enzyme has a lower affinity
for its substrate.
graph
9.
10. B.7.5 DESCRIBE THE MECHANISM OF
ENZYME ACTION, INCLUDING ENZYME
SUBSTRATE COMPLEX, ACTIVE SITE
AND INDUCED FIT MODEL.
11. enzymes are protein containing several
hundred amino acids
its conformation(3 dimensional shape) is
determined by the interactions between all the
R groups and is essential for its function
Some enzymes require the binding of non-
protein molecules for activity (co-factors)
Organic co-factors are called coenzyme-metal
ions
Inorganic co-factors acts as precursors for
coenzyme- vitamin
12. HOW DOES ENZYME FUNCTION?
Act as catalyst that will increase the rate of chemical
reaction without undergoing chemical change.
Lowers the activation energy of the reaction route
between substrate and product, so reaction can happen
more quickly at the same temperature.
This is because of the ability of enzyme to form a
temporary binding to the substrate where it is held by
relatively weak forces of attraction, forming an enzyme-
substrate complex.
Binding occurs at a small region of enzyme also known as
active site.
13.
14. Formation of complex depends on compatibility
between the substrate and the R groups of the
amino acids at the active site of enzyme.
It involves hydrophobic attractions, dipole-dipole
attractions, hydrogen bonds and ionic attractions.
The binding in the complex puts a strain on the
substrate molecule, and so facilitates the breaking
and forming bond.
Once the substrate has reacted, the product
formed no longer fits in the active site, so it
detaches.
Enzyme remains unchanged and is able to
catalyse further reaction.
15. ENZYMES ARE HIGHLY SPECIFIC FOR THE
REACTION THEY CATALYSE.
German chemist Emil Fischer proposed a model
known as the lock-and-key mechanism.
But recent work on proteomics has recognized that
enzymes are less rigid structures.
Danial Koshland suggested the theory ‘induced-fit
mechanism’.
In the presence of substrate, the active site undergoes
some conformational changes, shaping itself to allow
better fit.
