Metabolic Pathways

 Metabolic Pathways

Metabolic reactions are not independent reactions. In fact these are interdependent and constitute a series called metabolic pathways. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, each step being facilitated by a specific enzyme.

Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy which cannot be done by themselves, by coupling them to spontaneous reactions that release energy. Enzymes act as catalysts – they allow a reaction to proceed more rapidly – and they also allow the regulation of the rate of a metabolic reaction, for example in response to changes in the cell's environment or to signals from other cells.

The metabolic system of a particular organism determines which substances it will find nutritious and which poisonous. For example, some prokaryotes use hydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The basal metabolic rate of an organism is the measure of the amount of energy consumed by all of these chemical reactions.

Methods to study metabolic reactions

Several methods are employed to study metabolic pathways. These experimental approaches maybe broadly divided into 3 categories-

·        Use of whole organisms or its components.

·        Utility of metabolic probes.

·        Application of isotopes.

The actual methods employed for this purpose may be either in vivo (in the living system) or in vitro (in the test tube) or, more frequently, both as per the requirements of study.

 1. Use of whole organism or its components

 (a) Whole organisms- The purpose is to know the metabolism in the organism as a whole. Glucose tolerance test (CTT) employed to measure the response of a human body towards carbohydrate metabolism is an example of the use of whole organism.

 

(b) Isolated parts- organs, tissue slices, whole cells, sub cellular organelles, cell-free systems and recently purified components are frequently used to study metabolic pathways.

 2. Metabolic probes- Two types of metabolic probes are commonly used to trace out biochemical pathways. These are

• ·        Metabolic inhibitors 
• ·        Mutations

In both the cases, there is a specific blockade in a metabolic reaction which helps to understand the pathway. The inborn errors of metabolism in higher organisms and the genetic manipulations in the microorganisms have also given insights into the understanding of the metabolism.

 3. Use of isotopes- Isotopes are the atoms with the same number of protons but different no. of neutrons. By use of isotopes, the molecules of the living system can be labeled without altering their chemical properties.