Lock and key hypothesis


what is Lock and key hypothesis? what are the uses of Lock and key hypothesis? detailed explination about Lock and key hypothesis?

Lock and key hypothesis:-

This model assumes that enzyme and substrate have mutual complementary structure in their free state and are rigid molecules.

Any compound having complementary structure to the enzyme can bind to the enzyme and the reaction is possible where as any compound that takes complementary structure to the enzyme cannot bind to the enzyme and therefore the reaction is not possible.

The major limitation of the order {or} it is you that the substrate is rigid in such case it is not possible for the substrate getting converting into product.

It is known that enzymes undergo conformational changes when the binding of ligands such as substrate occurs.

Lock and key hypothesis,enzymes
Lock and key hypothesis

Induced fit model:-

It assumes enzyme is flexible and substrate is rigid.

The enzyme and substrate is lacks complementary structure in the free state.

When a substrate approaches an enzyme substrate induces conformational changes in the enzyme.

So that complementary structure are formed.

Any compound capable of inducing conformational changes in the enzyme resulting in the complementary structure can act as substrate where as any compound that fails to induce conformational changes in the enzyme to have complementary structures cannot act as substrate.

This model is considered analogue to hand {substrate} + nylon glow {enzyme}.

The model fails to explain the mechanism by which the substrate get converted in to the product.

Induced fit model
Induced fit model

Reversible non competitive inhibitior:-

A non competitive inhibitor binds reversibly at the site other than the active site and causes a change in the overall three dimensional shape of the enzyme that leads to a decrease in catalytic activity.

Since the inhibitor binds to at different site the substrate the enzyme may  bind to the inhibitor. The substrate or both the inhibitor and substrate together an example of non competitive inhibitor is the  action of  preparation rennin.

The effect of non competitive inhibitor connected overcome by increase in the substrate concentration so there is decrease in vmax.

The non competitive inhibitor the affinity of the enzyme for the substance is unchanged and 50 km remains same.

Line weaver burk plot showing the effect of non-competitive inhibition on km and vmax.

Engines have molecular weights ranging from about 12000 more than 1 million daltons.

Some enzymes require no chemical groups for activity other than the amino acid residues.

Others require an additional chemical components called cofactors -either one or more inorganic ions such as fe+2,mg+2,mn+2{or} zn+2{or}  a complex organic or  metallo-organic molecules called a coenzyme.


  1. Cu+2                                    –        cytochrome oxidase
  2. Fe+2/+3              –        cytochrome oxidase
  3. K+                                          –              pyravate kinase
  4. Mg+2                                   –               hexokinase, glu-6-phosphatase,pyruvate kinase
  5. Mn+2              –        arginase,ribonucleotide reductase.
  6. Mo                       –       dinitrogenase
  7. Ni+2                                      –              urease
  8. Se                        –       gluta thione peroxide
  9. Zn+2                     –       carbonic anhydrase,alcholdehydrogenase,carboxypeptidases

A co-enzyme {or} metal ion that is very that is very tightly or even covalently  bond to the enzyme protein is called prosthetic group.

A complete catalytically active enzyme together with its bound co-enzyme and {or} metal ions is called holoenzyme.

The protein part of such an enzyme is called the apo enzyme {or} apoprotein.

The distuinguishing feature of an enzyme catalysed reaction is that it take place within the confines of a pocket on the enzymes called the active site. The molecules that have bounded in the active site and acted upon by the enzyme is called substrate.

Gluconeogenesis  of carbohydrates from non-carbohydrate includes lactate, glycerol and some amino acids animal cells can carry out glycogen from 3c and 4 c prcure but not from two acetyl carbon of acetyl co-enzyme.

Gluconeogensis pathway:-

During gluconeogensis seven steps are catalysed by the same enzymes used to glycolysis.

These irreversible steps are :-

  1. Conversion of glucose to glu-61 ph by hexokinase.
  2. Conversion of f6 ph to f-16 br.ph by phospofructose kinase.
  3. Concentration of phosphoenol pyruvate by pyruvate kinase.

Concentration of pyruvate to pep:-

It cannot be convert directly

It requires two reactions:-

Pyruvate kinase step of glycolysis.

In pyruvate is converted to oaa catalyzed by pyruvate carboxylase.

The reaction occur in  mitochondria matrix

Oxaloacetate cannot cross the mitochondrial membrane because mitochondria have no transporter for oxaloacetate so oxaloacetate first reduce the malate mitochondria enzyme malate dehydrogenase at the expense of nadh.

Oxaloacetate + nadh + h+ ↔ malate + nad+

Mallet leaves the mitochondrial through a specific transporter in the inner mitochondrial membrane and in thecytosol it is reoxidised to oxaloacetate with production of cytosalic nadh

Mallet + nadh+ à oaa + nadh + h+

Second reaction by paramines pyruvate kinase in the conversion of oaa to pep catalysed by mn2required pep carboxy kinase.

Concentration of pyruvate to pep
Concentration of pyruvate to pep

Concentration of pep to glucose:-

Fructose 1,6 biph converts in to fructo 6 ph without atp

Glu-6 ph converts glu by glu 6 phosphate and no atp is required.

Concentration of pep to glucose
Concentration of pep to glucose

1 thought on “what is Lock and key hypothesis? what are the uses of Lock and key hypothesis? detailed explination about Lock and key hypothesis?”

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