Definition : Metabolism is the sum total chemical reactions occuring in the living system to sustain life.The word metabolism can also use to reffer all chemical reactions occuring within living system including digestion and the transport of substances into and between different
cells, in which case the set of reactions within the cells is called intermediary metabolism or intermediate metabolism. These processes allow organisms to grow and reproduce, maintain their
structures, and respond to their environments. Metabolism is usually
divided into two categories.
Metabolism is broadly divided into two categories :
1. Catabolism : The degradative or breakdown process of organic molecules to simpler ones, with a release of energy.
2. Anabolism : The biosynthetic processes in which energy is used to construct complex components of cells such as proteins and nucleic acids from simple precursors.
The chemical reactions of metabolism are organized in a metabolic pathway that constitutes a series of enzymatic reaction to produce specific products. Enzymes are crucial to metabolism because they allow organisms to drive
desirable reactions that require energy and will not occur by
themselves, by coupling them to spontaneous reactions that release
energy.Enzymes act as catalysts and allow these reactions to proceed quickly
and efficiently. Enzymes also allow the regulation of metabolic pathways
in response to changes in the cell's environment or signals from other
cells. The term metabolite is applied to a substrate or an intermediate or a product in metabolic reaction.
The metabolism of an organism determines which substances it will
find nutritious and which it will find poisonous. For example, some
prokaryotes use hydrogen sulfide as a nutrient, yet this gas is
poisonous to animals. The speed of metabolism, the metabolic rate, also
influences how much food an organism will require.
A striking feature of metabolism is the similarity of the basic
metabolic pathways between even vastly different species. For example,
the set of carboxylic acids that are best known as the intermediates in
the citric acid cycle are present in all organisms, being found in
species as diverse as the unicellular bacteria ''Escherichia coli'' and
huge multicellular organisms like elephants. These striking similarities
in metabolism are probably due to their early appearance in evolutionary history and being retained because of their high efficiency of different pathways.
Catabolism and Anabolism
Types of metabolic reactions
Metabolism of Carbohydrates
Metabolism of Lipids
Metabolism of Amino Acids
Metabolism of Nucleotides
Metabolism of Minerals
