This document discusses chemical kinetics and enzyme kinetics. It defines enzymes as biological catalysts that speed up chemical reactions without being used up in the process. The document describes how enzymes lower the activation energy of reactions and explains the mechanisms of enzyme action, including the lock and key and induced fit hypotheses. It also discusses Michaelis-Menten kinetics and how various factors like temperature, pH, cofactors, and inhibitors can affect the rate of enzyme activity. Allosteric enzymes are defined as having additional binding sites for effector molecules.

1. CHEMICAL KINETICS
AND ENZYMES
o Venus M Mafusire B223081B
o Michelle Mazwieguta B224068B
o Shingai P Mushapaidze B223350B
o Tatenda Mikili B224645B

2.  Chemical kinetics deals with rates of reactions and how
changes in concentration of components affect the rate of
chemical reactions
 Enzyme kinetics is the study of the chemical reactions
that are catalysed by enzymes.
 Enzymes are biological catalysts
 A catalyst is a substance that speeds up a chemical
reactions and remains unchanged at the end 0f the
reaction.

3. Types of Catalysts
 Catalysts provide a means of reducing the amount of energy
required to activate a reaction by providing an alternative
route/mechanism.
 Homogenous catalyst refers to reactions in which the
catalyst is in the same state as the the reactants,principally
in solution.
 Heterogenous catalyst refers to a reaction where the catalyst
and the substrates are in distinct states,typically solid-gas
respectively.

4. How enzymes lower the Activation Energy
 Catalysts lower the activation
energy of the transition state
by making it a rare and un-
stable intermediate.
 Transition state is the
intermediate state of the
reaction when the molecule is
neither a substrate or product

5. Mechanism of Enzyme Action
 Enzymes have two types of mechanisms being Lock and Key
hypothesis and induced fit hypothesis
 Lock and key hypothesis was proposed by Fischer and states that
“If the right key fits in the right lock,the lock can be opened,
otherwise not ,” by this he made it clear that enzymes are specific.

7. Induced fit hypothesis
 The induced-fit model was proposed by Koshland ,the model
suggests that an enzyme when binding with its
substrate,optimizes the interface through physical
interactions to form the final complex structure (enzyme-
substrate complex).
 Both the enzyme and substrate change shape slightly ,creating an
ideal fit for catalysis.

9. Michaelis-Menten Kinetics
 Michaelis-Menten model of enzyme kinetics explains how the rate of
an enzyme catalysed reaction depends on the concentration of the
enzyme and its substrate .
 Lets consider a rection in which a substrate(S) binds reversibly to an
enzyme (E) to form an enzyme-substrate complex (ES),which then
reacts irreversibly to form a product (P) and release the enzyme again.
S + E ES P + E
 Two important terms in Michaelis-Menten kinetics are :
• Vmax
• Km(Michaelis constant)

10.  Vmax – the maximum rate of reaction, when all enzymes active
sites are saturated with substrate.
 Km – the substrate concentration at which the reaction rate is
50% of the Vmax .Km is a measure of the affinity an enzyme has
for its substrate , as the lower the value Km , the more efficient the
enzyme is carrying out its function at a lower substrate
concentration.
 The Michaelis-Menten equation for the reaction above is :
 This equation describes how the initial rate of reaction (V) is
affected by the initial substrate concentration ([S]). It assumes
that the reaction is in the steady state, where the ES
concentration remains constant

13. Factors that affect the rate of enzyme
activity
 Temperature
 Effect of pH
 Effect of activators(Co-factors)
Concentration of enzymes
 Concentration of substrate
 Enzyme inhibitors

14. Temperature
 Enzymes operate fastest at an Optimum Temperature which is
about 40 degrees celcius.
 At very low temperatures enzymes become inactive and the rateof
reaction is low or nearly zero.
 As temperature increases the molecules gain kinetic energy so
the rate of collisions increases only upto the optimum
temperature.Temperatures above the Optimum temperature
results in the denaturing of enzymes (the vibration of molecules at
high temperatures causes the bonds that maintain the enzymes
3D structure to be brocken and the protein unfolds therefore the
active site is lost).

16. Effect of pH
 Enzymes function at an optimum pH which is about 7 to 8
however some may have an optimum just below for example
salivary amylase has an optimum pH of 6.8.
 When pH is above the optimum it affects the charge of the amino
acids at the active site, so the properties of the active site change
and the substrate can no longer bind (enzme is denatured).

18. Effect of activators(Co-factors)
 Co-factors are non-protein molecules required to activate
enzymes .
 Cofactors can be either inorganic (e.g., metal ions and iron-sulfur
clusters) or organic compounds (e.g., flavin and heme).
 Organic cofactors can be either prosthetic groups, which are
bound to an enzyme, or coenzymes, which are released from the
enzyme's active site during the reaction e.g NADH, NADPH and
adenosine triphosphate.
 Coenzymes are small organic molecules that can be loosely or
tightly bound to an enzyme.
 Tightly bound coenzymes can be called allosteric groups.
 Coenzymes transport chemical groups from one enzyme to
another.

19.  Some of these chemicals such as riboflavin, thiamine and folic
acid are vitamins (compounds that cannot be synthesized by the
body and must be acquired from the diet).
 The chemical groups carried include the hydride ion (H-) carried
by NAD or NADP+, the phosphate group carried by adenosine
triphosphate, the acetyl group carried by coenzyme A, formyl,
methenyl or methyl groups carried by folic acid and the methyl
group carried by S-adenosylmethionine.

20. Concentration of enzymes
 With increase in enzyme
concentration there is
increase in the rate of
reaction as there are
more active sites.

21. Concentration of substrate
 As the substrate concentration increases there is increase in the
rate of reaction as collision between the substrate and enzyme
active sites increase,however when there is a high concentration
of substrate the enzyme active sites become concentrated and
the rate of reaction remains constant

23. Enzyme inhibitors
 Enzyme inhibitors are compounds which modify the catalytic
properties of the enzyme and therefore slow down the reaction
rate
 There are two types of inhibition being competitive and non-
competitive inhibition.
 Competitive inhibitors have a shape which is complimentary to
that of the substrate and hence fits into the enzymes active site
and usually competitive inhibition is reversible.
 Non-competitive inhibitors bind to another part of the enzyme
molecule, changing the shape of the whole enzyme, including the
active site, so that it can no longer bind substrate molecules.

24.  Non-competitive inhibitors bind tightly and irreversibly

25. Allosteric Enzymes
 Enzymes that have an additional binding site for effector
molecules other than the active site.

26.  An example of an allosteric inhibitor is ATP in cellular respiration ,
this metabolic process operates in a feedback loop .The high
ratio of ATP to ADP will inhibit Phosphofructokinase(PFK) and
glycolysis