Enzymes are biological catalysts that speed up a chemical reaction without after itself, the term enzyme was first of all used by German scientist Wilhelm Kuhne in 1878.Â
The sum of all biochemical reactions going on within a living organism is
called metabolism The set of biochemical reactions that occur in living
organisms to maintain life is called metabolism, the term metabolism
is derived from the 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:Â The process in which large molecules are
broken down into simpler molecules by releasing energy is called
catabolism.
Example: - Respiration  Â
    C4H12O6 + 6O6 ⟶ 6O2 + 6H2O +
Energy
    Sucrose + H2O ➡ Glucose + Fructose + ATP
(ii) Anabolism: The process in which small molecules combine
to form large molecules by utilizing energy is called anabolism.
Example: - Photosynthesis (On sunlight)
6O2 + 12H2O ⟶ C6H12O6 + 6O2 + 6H2O
Glucose + Fructose + ATP ⟶ Sucrose + H2O
The Characteristics of all living things such as breathing, reproduction growth, and response to stimuli are the outcome of biochemical reactions taking place inside the body of living organisms. All these reactions are controlled by specific proteins called enzymes.
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Characteristics of Enzymes
Enzymes are the biochemical catalyst and possess the following important
characteristics of enzymes.
1. Nature: Enzymes are proteins in nature and are secreted by
cells.
2. Catalysts: They act like catalysts 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 amounts: Enzymes are required in very small
amounts as compared to the amount of substance.
5. Specific active center: Enzymes have a specific active center
called the active site, which is attached to the substances.
6. Sensitivity: Enzymes are sensitive to changes in 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:Â Enzymes are not consumed during the
biochemical reactions and can be used again and again.
11. Enzyme Inhibitors: Some substance that interacts with enzymes to prevent them from working are called enzyme inhibitors e.g., poison, drugs, etc. Inhibitors determine?Â
12. Lower the Activation Energy:Â Enzymes do not initiate the
reaction but increase the rate of reactions by lowering the activation energy
that is required for the substance.
Types of Cofactors and Cofactor of EnzymesÂ
The cofactor is a non-protein organic chemical compound that is required for an enzyme
as the catalyst. It can be considered helper molecules for enzymes the main types of
cofactors are prosthetic groups, coenzymes, and activators.
(a) Prosthetic groups:Â It is a type of cofactor that is firmly
bound to the enzyme and cannot be removed without denaturing is called prosthetic
groups, e.g., Flavin mononucleotide (FMN) and Flavin adenine dinucleotide
(FAD).
(b) Coenzyme: A type of cofactor derived from vitamins that are
loosely bound to the enzymes and can be readily separated from enzymes is called
coenzyme.
(c) Activations: These are metal ions that form temporary
attachments with enzymes, e.g. Zinc, Iron, etc.
Activation Energy of Enzymes
The energy required to initiate a chemical reaction is called activation
energy, all chemical reactions require activation energy.
Enzyme Lower Activation Energy
When a chemical reaction takes place some amount of energy is required to break
chemical bonds in the reactant (substrate) such energy is called activation energy.
Enzymes lower 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 the correct orientation.
For example: For the reaction 2H2O2 → 2H2 + O2 the activation
energy is 86 kJ/mole is required without a catalyst and just 1 kg/mole energy is
required in the presence of the enzyme.
Specificity of Enzymes
Enzymes 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, an enzyme that
catalyzes one reaction may not catalyst another.
Example:Â (a) catalase: -Â catalase is an enzyme that
only catalyzes the decomposition of hydrogen peroxide.   H2O2 →
H2 + O2
(b) Protease: -Â It is an enzyme that converts proteins into
amino acids.Â
 protein ⟶ Amino acids + Energy
(c) Amylase: -Â Amylase enzyme works only for the digestion of
starch.
(d) Lipase: -Â Lipase enzyme converts lipids into omi fatty acid
and glycerol.Â
lipids ⟶ fatty acid + glycerol
The specificity of different enzymes is determined by the shape of their active
site the active site possesses specific geometric shapes that fit with the substrate.
Mechanism of Enzyme Action
Mechanism of enzyme action lock and key model:
There is a small protein in an enzyme that is involved in catalysis. It is in
the form of a depression or pocket on the surface of an enzyme molecule. When an
enzyme is attached to the substrate it is from the enzyme substrate complex the active
site of the enzyme catalyzes the reactions and into the product, the enzyme substrate
complex breaks, and the enzyme and the product are released.
Enzyme + Substrate ⟶ enzyme - Substrate ⟶ Enzyme + Product
There are two models which explain the mechanism of enzyme action.
Lock and Key model: - This model was presented by German scientist Emil
Fisher in 1894 according to this model enzymes act as a lock and substrate acts
as a key.
Main Point: -Â One specific key can open only a specific lock.
In the same manner, the specific enzyme can transfer only specific substrates
into products. The enzyme must have the correct geometric shape to fit the
substrate. According to this model, the active site has a rigid structure.Â
There is no modification in the active site before during or after the
reaction. Â