Enzymes Definition and Activation Energy

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. 

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

Types of Metabolism

(i) Catabolism: The process in which large molecules are broken down into simpler molecules by releasing 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 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: 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? 

12. Lower the Activation Energy: 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 Enzymes 

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: 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.

Enzyme lower activation energy

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: (a) catalase: - catalase is an enzyme that only catalyzes the decomposition of hydrogen peroxide.     H2O2 → H2 + O2

(b) Protease: - It is an enzyme that converts proteins into amino acids. 

 protein Amino acids + Energy

(c) Amylase: - Amylase enzyme works only for the digestion of starch.

(d) Lipase: - Lipase enzyme converts lipids into omi fatty acid and glycerol. 

lipids fatty acid + glycerol

Specificity of Enzymes


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: - 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. 

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


BANTI SINGH

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