What is metabolism?

All living cells require energy and materials for the building and functioning of their living matter. These energy and materials are synthesized or produced by organisms through different chemical or biochemical reactions. The sum total of all the chemical or biochemical reactions that occur in an organism is called Metabolism. These chemical/biochemical reactions are catalyzed by organic catalysts called enzymes. Each enzyme is highly specific and separate enzymes are required for the separate biochemical reactions.

Metabolism is of two types (i) Anabolism and (ii) Catabolism.

Anabolism (Constructive Metabolism): It is the set of metabolic or biochemical pathways that construct different complex molecules from smaller units and are also called “building up” reactions. Example: Synthesis of an organic compound such as sugar using H2O and CO2 during photosynthesis, synthesis of protein from 20 different amino acids, and synthesis of starch from glucose monomers. Energy is stored as potential energy during the anabolic process. The anabolic process is required for the growth and development of an organism.

Catabolism (Destructive Metabolism): It is the set of metabolic or biochemical pathways that involves the breaking of complex molecules and substances into a smaller and simple form. Upon breakdown, the potential energy stored in the molecules is converted into kinetic energy. Example: Polysaccharides such as starch (plants) and glycogen (animals) are degraded into simple sugars such as glucose, breakdown of sugar molecules during respiration. Breakdown of sugar releases energy in the form of ATP. Proteins are degraded into different amino acids and fats are degraded into fatty acids and glycerol.

The metabolism (anabolism and catabolism) of an organism can be affected due to external or environmental factors such as light, temperature, pollution, environmental toxin, and internal factor such as stress, diseases as well as genetic factor. Inborn errors of metabolism are rare genetic disorders that arise due to change in DNA sequence or mutation in a protein-coding or enzyme coding gene. Due to which the body synthesized nonfunctional proteins (enzymes) that unable to break down or metabolize food or parts of food. Example:  Phenylketonuria is caused due to mutation in the enzyme, phenylalanine hydroxylase which results in decreased metabolism of the amino acid phenylalanine.

Frederick Griffith’s Experiment: Bacterial Transformation

In 1928, British bacteriologist Frederick Griffith had carried out a series of experiments using bacteria Streptococcus pneumoniae which causes pneumonia in human. In his experiments, Griffith used two related strains of bacteria, known as R (Rough, non-virulent) and S (Smooth, virulent).

The Experiment

1. When Griffith infected mice with the non-virulent bacteria (R strain), the mice did not develop pneumonia and survived.

2. When Griffith infected mice with the virulent bacteria (S strain), the mice developed and died.

3. When Griffith infected mice with heat-killed virulent bacteria (R strain), the mice did not develop pneumonia and survived as the bacteria had been died due to heat.

4. When Griffith infected mice with a mix of heat-killed virulent bacteria (S strain) and living non-virulent bacteria (R strain), the mice were found to developed pneumonia and died.

Griffith concluded that the R strain had been “transformed” into the lethal S strain by a “transforming principle” which allowed R strain to “transform” into S strain (smooth, polysaccharide capsule coated) bacteria and become virulent.