Enzymes

Enzymes

Meaning:

Enzyme = En + zyme 

Means En - In  , zyme - living 

The word 'enzyme' was coined by W.Kuhne (1878) while working on fermentation

Enzymes may be defined as organic substances capable of catalysing chemical reactions in the living systems 

These are the following points necessary for to be the enzyme:-

a) Proteinaceous substance 

b) Biological and organic catalysts

c) Required in small quantity

d) Specific in nature

TYPES:

a) On the basis of structure:

1) Simple protein enzymes:

Such enzymes are wholly made up of proteins

e .g. trypsin, pepsin , amylase , urease

2)Conjugated enzymes:

In such enzymes , non protein parts are also the structural components.

The protein part is called Apoenzyme and non - protein component is called cofactor

Isoenzymes:

Such enzymes are different in molecular structure but are similar in function

e.g. Lactic acid and dehydrogenase (LDH)

b) On the basis of presence:

1).  Inducible enzyme :

Such enzymes do not occur in the absence of substrate

e.g Nitrate Reductase ( Nitrate Reductase is found in the nodules of leguminous crop)

2) Non inducible enzyme : Such enzymes are present at all the times 

e.g. mostly enzymes

Mode of action:

  The enzyme substrate relationship is often compared to as 'Lock and key' theory , proposed by Fischer (1894) 

Classification:

The enzymes are broadly classified into six groups:

1)  Transferases:

Such  enzymes catalyse the transfer of one carbon group to another molecule

e.g. Hexokinases 

2)Hydrolases: 

Such enzymes catalyse the hydrosis of the compound 

i.e. the addition of the water molecule

e.g. C6H22O11 + H2O-------- C6H12O6+ C6H12O6 

Invertase , Amylase , phosphatase

3) Oxido- reductases:

3a) Oxidases:

Such enzymes catalyse the oxidation with moleculer oxygen 

e.g. Cytochrome oxidase , peroxidase

3b) Dehydrogenase:

Catalyse the removal of 'H' through oxidation concerned with oxidative phosphorylation

e.g. Alcohol dehydrogenase

3c) Reductases:

  These enzymes cause addition of H or electron and removal of O2 

E.g. Nitrate Reductase

4) Lyases:

These enzymes cause the removal of a group of atoms from the substrate and cause addtion of 2nd group at this double bond without affecting hydrolysis oxidation and reduction

e.g. Carboxylase , Fumerase , adolase

5) Isomerases: 

These Enzymes are the responsible for the isomeric changes through rearrangement

6) Ligases or Synthatases:

 These catalyze the synthesis of different types of bonds p

e.g. Polymerase , RNA synthtase

Nature and properties of Enzymes:

 

1) Enzymes are specific in nature means specific in reaction with substrate

2) Enzymes are colloidal in nature and thus provide large surface area for reaction

3) are required in extremely small amounts

4) remain unaffected in the reaction

5)Organic catalyst

6)are pH regulated

 7) Thermolabile ( means heat sensitive)

8) Enzyme activity can be inhibited

9) Enzymic reactions are reversible but forward reaction is more

Factors affecting Enzymic reactions

1) Substrate Concentration:

An increase in the concentration of the substrate firstly increases the rate of the reaction but when all the active sites of the enzyme surface are occupied by the substrate molecule , the increase is stopped

2) Enzyme concentration:

Firstly there is an increase in the rate of reaction with the increse in enzyme concentration but the rate of reaction stops at a point and becomes constant when substrate con. becomes the limiting factor

3) Temperature:

The Enzymic reaction rate increases twice for every rise of 10°C within the certain limit 

4) The hydrogen ion concentration (pH)

 The  pH between 7-7.5 is ideal for the normal Enzymic activity

5) Hydration :

In seeds , the amount of water is too less so no Enzymic activity is observed.

With the increase in the amount of water , enzymes become active and seed starts to germinate 

6) Concentration of the End Product:

Enymzymic reactions are reversible in nature and acts on the 'Mass action' principle

7) Inhibitors :

Enzyme inhibitors are of two types:

Enzyme inhibitor

Reversible: Such inhibitors are removed by dialysis 

1)  Competitive inhibitors:

Such inhibitors are structurally similar to the substrate molecule

e .g. Malonic acid resembles with succinic acid 

2) Non competitive inhibitors:

 Such.  Inhibitors reacts with either enzyme or enzyme substrate complex 

e.g. cyanides , azides

Irreversible:

Such inhibitors can not be removed because they probably alter or destruct the active sites of the enzymes

✍️Agricos

Vaishnavi Nimkar 🌾🌱