Regulation of Enzyme Action

 Regulation of Enzyme Action:

A large variety of chemical reactions occur in a cell simultaneously in a surprisingly coordinated manner, without in any way interfering with one another. Each compound is produced when required and in the desired quantity. Such a precise regulation is achieved by two types of  control mechanisms operating in the cells. One mechanism operates at the enzyme level and the other at the gene level.

1): Control at the Enzyme Level:

In this type of control mechanism, the enzyme, substrate and product  themselves regulate the chemical reactions. When the product of an enzyme reaction accumulates in the cell, it inhibits its own production by lowering the enzyme activity. This kind of control mechanism is called feedback inhibition, or negative feedback. 

  Substrate ➡️➡️➡️➡️ Products

   The feedback Inhibition is analogous to a refrigerator thermostat which regulates temperature by switching off and on the electric supply in response to temperature variation inside the refrigerator. 

  Synthesis or degradation of a compound in a cell often involvs a series of intermediate enzyme__ controlled reactions. Inhibition of any one of the enzymes affects the entire series of reactions. This may adversely affect the cell and many cause its death. 

   A specific instance is cited to illustrate the above fact. A colon bacterium Escherichia coli synthesises the amino acid isoleucine from a substrate isoleucine accumulates in amount more than required,  it stops it's own production by inhibiting the activity of the enzyme threonine deaminase which catalyzes the first reaction of the series.This type of metabolic control, in which the first enzyme of a series is inhibited by the end product, is known as end__ product Inhibition. 

2): Control at the Gene Level:

In this type of control mechanism, the gene regulates the production of enzyme. Proteins are the end product of gene ( DNA) action. They are synthesized as summarised below__

 The gene responsible for synthesis of enzyme is activated and inactivated by the substrate to be metabolised and the end product accumulating in excess respectively. The process is quite elaborate and beyond the scope of this book.


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