Enzymes are biological catalyst which speed up a chemical
reaction without after itself, the term enzyme was first of all used by German
scientist Wilhelm Kuhne in 1878.
Metabolism
The sum of all biochemical reactions going on within a living organism is
called metabolism Or The set of biochemical reactions that occur in living
organisms in order to maintain life is called metabolism, that terms metabolism
is derived from Greek word meaning '' Change the concept of metabolism use of
all given by Lbn-e-Natees who stated that the body and its parts always
undergoing change, there are two types of metabolism. Catabolism and
Anabolism.
Types of Metabolism
(i) Catabolism: The process in which large molecules are
broken down in to simpler molecules by releasing of energy is called
catabolism.
Example: - Respiration
C4H12O6 + 6O6 ⟶ 6O2 + 6H2O +
Energy
Sucrose + H2O ➡ Glucose + Fructose + ATP
(ii) Anabolism: The process in which small molecules combine
to from large molecules by utilizing of energy is called anabolism.
Example: - Photosynthesis (On sun light)
6O2 + 12H2O ⟶ C6H12O6 + 6O2 + 6H2O
Glucose + Fructose + ATP ⟶ Sucrose + H2O
The Characteristics of all living thing such as breathing, reproduction growth and response to stimuli are the outcome of biochemical reactions taking place inside the body of a living organisms. All these reactions are controlled by specific proteins called enzyme.
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Characteristics of Enzymes
Enzymes are the biochemical catalyst and possess the following important
characterizes of enzymes.
1. Nature: Enzymes are proteins in nature and are secreted by
cells.
2. Catalyst: They act like catalyst and speed up a biochemical
reaction.
3. Specific for reaction: Enzymes are specific in action they
are not specific only for substance but also for the kind of biochemical
reactions.
4. Used in small amount: Enzymes are required in very small
amount as compared to the amount of substance.
5. Specific active center: Enzymes have specific active center
called actives site, which is attached to the substances.
6. Sensitivity: Enzyme are sensitive to the changing of temp.,
pH, etc. these may stop their activity.
7. Intracellular Enzymes: Some enzymes are found inside the
cells called intracellular enzymes. e.g., mitochondria enzymes.
8. Extracellular Enzymes: Some enzymes work outside the cells
called extracellular enzymes. e.g., lipase, amylase, pepsins, etc.
9. Need a factor: Some enzymes work properly when a cofactor
is attached.
10. Remain unaffected: Enzymes are not consumed during the
biochemical reactions and can be used again and again.
11. Enzyme Inhibitors: Some substance interacts with enzymes to prevent it from working is called enzyme inhibitors e.g., poison, drugs etc. Inhibitors determine?
12. Lower the Activation Energy: Enzyme do not initiate the
reaction but increase the rate of reactions by lowering the activation energy
which is required for substance.
Types of Cofactors and Cofactor of Enzymes
Cofactor is a non-protein organic chemical compound that is required for an enzyme
as catalyst. It can be considered helper molecules for enzymes the main type of
cofactor is prosthetic groups, coenzyme and activators.
(a) Prosthetic groups: It is a type of cofactor that is firmly
bound to enzyme and cannot be removed without denaturing is called prosthetic
groups, e.g., Flavin mononucleotide (FMN) and Flavin adenine dinucleotide
(FAD).
(b) Coenzyme: Type of cofactor derived from vitamins that is
loosely bound to the enzymes and can be readily separated from enzyme is called
coenzyme.
(c) Activations: These are metal ions which from temporary
attachment with enzyme, e.g. Zinc, Iron, etc.
Activation Energy of Enzymes
The energy required to initiate chemical reaction is called activation
energy, all chemical reaction required activation energy.
Enzyme Lower Activation Energy
When chemical reaction take place some amount of energy is required to break
chemical bonds in reactant (substrate) such energy is called activation energy.
Enzymes lower off the amount of a taster rate. Enzymes act in many ways to
lower the activation energy, for example, they change the shape of substrate
molecules or bring them in correct orientation.
For example: For the reaction 2H2O2 → 2H2 + O2 the activation
energy is 86 kJ/mole is required without catalyst and just 1 kg/mole energy is
required in the presence of enzyme.
Specificity of Enzymes
Enzyme are generally very specific in their action; they are specific not
only for substrate but also for the kind of reaction. Every enzyme due to its
special chemical structure can recognize a particular substrate, enzyme that
catalyst one reaction may not catalyst another.
Example: (a) catalase: - catalase is an enzyme which
only catalyze the decomposition of hydrogen peroxide. H2O2 →
H2 + O2
(b) Protease: - It is an enzyme which convert proteins in to
amino acids.
protein ⟶ Amino acids + Energy
(c) Amylase: - Amylase enzyme work only for the digestion of
starch.
(d) Lipase: - Lipase enzyme convert lipids into omi fatty acid
and glycerol.
lipids ⟶ fatty acid + glycerol
The specificity of different enzymes is determined by shape of their active
site the active site possess specific geometric shapes that fit with substrate.
Mechanism of Enzyme Action
Mechanism of enzyme action lock and key model:
There is a small protein in enzyme that is involved in catalysis. It is in
the form of a depression or pocket on the surface of enzyme molecule. When an
enzyme attached with the substrate it from enzyme substrate complex the active
site of enzyme catalyzes the reactions and into product, the enzymes substrate
complex breaks and the enzyme and the product are released.
Enzyme + Substrate ⟶ enzyme - Substrate ⟶ Enzyme + Product
There are two models which explain mechanism of enzyme action.
Lock and Key model: - This model was presented by a German scientist Emil
Fisher in 1894 according to this model enzyme act as a lock and substrate act
as key.
Main Point: - As one specific key can open only a specific lock.
It the same manner the specific enzyme can transfer only specific substrate
into products. The enzyme must have the correct geometric shape to fit the
substrate. According to this model the active site has rigid structure.
There is no modification in the active site before during or after the
reaction.
