Different Models of Enzyme action

 TWO HYPOTHESIS OR MODELS OF ENZYME ACTION:

 Following two hypothesis were given to explain mode of action of enzyme .

1-LOCK AND KEY HYPOTHESIS:

This model was proposed by EMIL FISHER in 1894.

Emil fisher suggested that each has fixed particular shape and have fixed where substrate binds fit exactly and changes into products.

According to this hypothesis enzyme is LOCK while substrates is KEY as key has same shape to that keyhole of lock in same manner key has exact shape similar to active site of an enzyme thus substrate bind fits exactly in enzyme and substrate changed into product.

If the substrate and enzyme active site shape is not similar so substrate will be unable to bind with enzyme active site and thus no reaction occurs.

According to this hypothesis Active site is rigid structure.

According to this hypothesis enzyme is very specific in their action and can carry out only one particular reaction this property of enzyme is called SIGNIFICANT PROPERTY.

The enzymes which work according to this hypothesis is called NON REGULATORY ENZYMES.

When one enzyme catalyzes only one specific substrate and not other substrate is called as ABSOLUTE SPECIFICITY.(UREASE).

  UREA + WATER   =  AMMONIA + CARBON DIOXIDE

EXAMPLES OF LOCK AND KEY ENZYMES:

Only small amount of enzymes follow this hypothesis of enzyme action like maltase,sucrase and urease etc.

2-INDUCED FIT MODEL:

This model was proposed by DANIEL KOSHLAND in 1959.

According to this hypothesis enzyme active site is flexible it modifies itself when different substrate attach to it.

According to studies these type of enzyme  catalytic site has aminioacids which allow active site to modify its shape for different substrate and enzyme perform its function effectively.

When substrate changes into product enzyme gets its original structure again.

This model flexibility of enzymes and shows that active site of an enzyme is flexible and enzyme can convert different types of substrate into product.

This enzyme can carry more reactions.

According to this hypothesis substrate is hand while enzyme is gloves .gloves change shape temprorly when different size of hands fit into it.

Those enzymes which follow this model is called  REGULATORY ENZYMES.

EXAMPLES:

The best example of regulatory enzyme is carbonic anhydrase which add oxygen to heamoglobin and as well as also control function of carbonic acids and bicarbonate ion.

HB + 4O2    = HB4O2(OXYHEAMOGLOBIN)

DIFFERENCE BETWEEN INDUCED AND LOCK MODEL:

According to induced model enzyme is flexible while according to lock model enzyme active site is a rigid structure.

According to induced model enzyme active site can undergoes conformational change to improve binding but according to key model enzyme is specific in structure and can undergoes particular reaction.

IMPORTANT MCQS IN THIS TOPIC:

1-Lock and key model proposed by:

Answer: EMIL FISHER

2--Lock and key model is proposed in:

Answer: 1894

3-According to which model active site of enzyme is hard:

Answer: LOCK AND KEY

4-Which model enzymes are non regulatory enzymes:

Answer: LOCK AND KEY

5-Allosteric enzymes is another name for:

Answer: REGULATORY ENZYMES

6-Catalytic site of enzyme has _aminoacids:

Answer: 2-4

7-Induced fit model proposed by:

Answer: DANIEL KOSHLAND 

8-Induced fit model proposed in:

Answer: 1959

9-Active site has _functional regions:

Answer: 2 

10-The enzyme which catalyzes only one substrate not other this property is called:

Answer: ABSOLUTE SPECIFICITY

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