Enzymes

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What are Enzymes

Enzymes are bio catalyst which speed up the chemical reactions by lowering Energy of Activation.

Energy of Activation

Amount of energy which is required to start a chemical reaction

or

Energy required to break a bond (particularly covalent bond) present in reactant

Nomenclature of Enzymes

Enzyme is a Greek word formed by two component En ( means In) and Zyme (means yeast). Term enzyme was coined by F.W. Kuhne in 1978.

Nature of Enzymes

Almost all enzymes are protien in nature except few which are nitrogenous acid like RNA-DNA (Ribozymes).Ribozymes catalyze reaction in genetic informations.

Characteristics of Enzymes

  • Protein in nature and are formed of living cells
  • May be intracellular or extra cellular.
  • Remains unchanged during and after the reactionSpeed up the rate of reaction by decreasing energy of action
  • Specific in their nature
  • Heat sensitive and act on particular(optimum) temperature.
  • Each has specific substrate pH for its activity
  • Action can be alter by activators and inhibitors.

Classification of Enzyme on the basis of structure

Pure or simple enzyme consist of protein ( For example Amylase and Pepsin). Conjugated or Holoenzyme  may contain a non protein part (called Prostheic group) as well (For example phosphate and peptidase)

Holoenzyme = Apoenzyme + Prosthetic group

Where Apoenzyme is protein part, and Prosthetic group is non protein part

Classification of Enzyme on the basis of functions

  1. Oxidoreductases

    Catalyze reactions in which one substrate is oxidized while other is reduced. Sub classes are :

    • Dehydrogenases ( convert single bond to double bond)
    • Oxidases ( use oxygen as oxidant)
    • Peroxidases (use H20 as oxidant)
    • Hydroxylases (introduce hydroxyl group)
    • Oxygenases (introduce mol. Oxygen in place of double bond)
  2. Transferases

    Transfer one carbon group ( For example methyl) from one substrate to another substrate.

  3. Hydrolases

    Catalyze hydrolytic cleavage of C-O, C-N, C-C and P-O bonds and other single bonds (For example Peptidases, Esterases, Glycosiderases and Phosphatidases)

  4. Lyases

    Catalyze elimination reactions to form double bond and reversible reaction by adding groups across double bond. For example Decarboxlases, Aldolases and Dehydratases.

  5. Isomerases

    They alter the structure but not the atomic composition by moving a group from one position to another in one molecukle. For example Epimerases, Mutases.

  6. Ligases

    Catalyze reaction in which two molecules are joined. They arte also known as synthtases.

Role of Enzyme

Enzyme react with energy rich or energy poor molecules and forms an intermediate complex that breaks into product andEnzyme

  • Substrate = Enzyme + Complex
  • Complex= Product + Enzyme

The equilibrium is achieved if the ratio of conc of reactants (substrate) and product remains same. Rate of reaction is 1/μ

Mode of Action of Enzymes

  1. The action of enzyme depends on its chemical structure. A typical enzyme molecule hass a 3D structure
  2. Has depression or pit for substrate (to fit in) known as “Active Site”
  3. Anyother site other thant active site is called Allostertic Site

There are two theories of enzyme action which are known as

  1. Lock and Key Model
    Proposed by Fischer (1898) and modified by Paul Filder and D.D. Woods according to this model
    – The active site of enzyme has distinct shape
    – It allows few substrate to fit in (like a particular lock allow particular key to fit in )
    – Enzyme breaks substrate to product
  2. Induce Fit Model
    Proposed by Koshland(1959), it states that
    – Enzyme binds with substrate- This binding induce changes in enzyme structure
    – Due to this change enzyme acts and forms product

Factors affecting Enzyme Activity

The activity of enzymes depends on following factors

  1. Substrate Concentration
    – Increase with increase in substrate concentration ( up to a limit)
    – At very high concentration, activity again decreases due to saturation of enzyme with substrate and saturation of product that is higher concentration of product.
  2. Temperature
    – Increases with in temperature ( upto limits)
    – Maximum activity at optimum temperature.
    – Highly active at 37°C and destroyed at 100°C
    – At 0°C there is minimum activity.
  3. pH
    Enzymes are pH specific i.e. work in specific pH because of protein which can act both in acidic and basic medium.
  4. Water
    Enzyme activity is usually maximum ( upto limits) but decreases after limits (dilution of enzyme)
  5. Radiation
    Enzymes become inactive due to radiations including Alpha, Beta, Gamma rays.
  6.  Co-Enzyme and Activators
    Induce the enzyme activity

Things to Remember

Inhibitors

Substances which decreases the activit of enzymes

Competetive Inhibitors

Inhibitor molecules which resemble the normal substrate molecule and compete for admission into the active site. They block the subtrate from entering active site.

Non-competetive Inhihibitors

Inhibitors bind to a part of the enzymes away from the active site (Allosteric site) . This binding cause change in the enzyme molecule shape and decrease in enzyme activity.

Feedback inhibitation

Common biological control mechanism of brain in order to regulate enzyme activity

Prosthetic Group

Non-protien part of enzyme (also known as Co-Enzyme or Co-Factor)

Co-Enzyme

When prosthetic group consist of organic molecules (like FAD/NAD)

APOENZYME

Protein part of enzyme

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Practice Test 1 for Enzymes

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