Enzymes Definition and Activation Energy

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.  


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

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 ‚ě° 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 ‚ü∂ C6H12O6 + 6O2 + 6H2O

Glucose + Fructose + ATP ‚ü∂ 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.

Enzyme lower activation energy

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 ‚ü∂ fatty acid + glycerol

Specificity of Enzymes

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 ‚ü∂ enzyme - Substrate ‚ü∂ 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. 

Mechanism of Enzyme Action

There is no modification in the active site before during or after the reaction.  

 Fundamentals of biochemistry | Biochemistry 

 Genetic Some Basic Fundamentals | Fundamentals of Genetics and Genomics


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