Dynamic State_ Concept of Metabolism:

In the above account, we have described that cells of living organisms ( e.g., bacteria, protozoa,plants or animals) contain large number of inorganic and organic compound ( biomolecules) in definite concentrations. All organic biomolecules are constantly being broken down or built up through chemical reactions. Such chemical reactions are together termed metabolism. Every chemical reaction occurring in a cell is a catalyzed reaction. The catalysts which hasten the rate of given metabolic conversions are also proteins ( biomolecules).

What we have learnt till now is that living organisms, be it  simple bacterial cell, a protozoans, a plant  or an animal, contain thousands of organic compounds. These compounds or biomolecules are present in certain concentration ( expressed as mols/ litre etc.) One of the greatest discoveries ever made was the observation that all.these biomolecules have a turn over.This means that they are constantly being changed into some other biomolecules and also made from some other biomolecules. This breaking and making is through chemical reactions constantly occurring in living organisms. Together a these chemical reactions are called metabolism. Each of the metabolic reactions results in the transformation of biomolecules. A few examples for such metabolic transformations are: removal of CO2 from amino acids making an amino acid into an amine, removal of amino group in a nucleotide base; hydrolysis of a glycosidic bond in a disaccharide, etc. We can list tens and thousands of such examples.Majority of these metabolic reactions do not occur in isolation but are always linked to some other reactions. In other words, metabolites are convert into each other in a  series of linked reactions called metabolic pathways.These metabolic pathways are similar to the automobile traffic in a city. These pathways are either linear or circular. These pathways criss_ cross each other, i.e., there are traffic junctions. Flow of metabolites through metabolic pathways has a definite rate and direction like automobile traffic. This metabolite flow is called the dynamic state of body constituents. What is most important is that this interlinked metabolic traffic is very smooth and without a single reported mishap for healthy conditions.  

Feature of the metabolic reactions is that every chemical reaction is a catalysed reaction. There is no uncatalysed metabolic conversion in living systems. CO2 dissolving in water, a physical process, is a catalysed reaction in living systems. The catalysts which hasten the rate of a given metabolic conversion are also proteins. These proteins with catalytic power are named enzymes. 

Meaning of Metabolism:

The term metabolism refers to the sum of all the enigmatically catalyzed chemical reactions constantly taking place in the cells and tissues of the living organisms. These include those that change the small molecules into large ones as those which convert the large molecules into small ones.

A product of metabolism is called a metabolite.In other words, the biomolecules have a turn over.i.e., they are constantly being changed into some other biomolecules and are being made from some other biomolecules involving  chemical reactions.

Majority of the metabolic reactions do not occur in isolation,i.e., they are always linked to some other reactions. In other words, metabolites are converted into each other in a series of linked reactions ( linear or circular) called metabolic pathways. The metabolite flow through metabolic pathways has  a definite rate and direction.In the cells or tissues, these metabolic pathways criss_ cross each other and, therefore, the metabolite flow is called the dynamic state of the constituents. In healthy state of a living organism, metabolite flow is very smooth and flawless.

  Metabolism enables the living organisms to use matter and energy to build up, maintain, and renew their parts. The ability to transform environmental materials into their own specific body substance is one of the characteristics that distinguishe the living things from the non_ living objects.


Metabolism has two forms: anabolism and catablism.

1): Anabolism: 

Anabolism is the process by which the large, complex chemical compounds,cell organelles and cell products are built up from the small, simpler compounds in the body of a living organism, usually with the use of energy (G.anabole = a raising up; ana= up ➕ bole = a stroke).Because anabolism consumes energy, it is an endergonic process .This energy may be stored in the chemical bonds of the anabolic products__ 

AB➡️AB[ ➕🔼 G].G is Gibbs free energy. Anabolism results in growth and increase in the body weight. It is therefore, also called constructive, or building up, metabolism. Any substance formed as a result of an anabolic process is known as anabolite.

Example: Formation of protein from amino acids.

 2): Catabolism: 

Catabolismis the process by which the large, complex chemical compounds breakdown into  the small, simpler compounds in the body of a living organismoften accompanied by the liberation of energy  (G.katabole = a casting down; kata = down + ballein  = to throw).It is also spelled as katabolism.Beacuse catabolism releases energy, it is an exergonic process ___ AB ➡️A➕B[➖🔼G].This energy may be used in some endergonic  reaction or in some activity, such as movement. Sometimes,  the simpler molecules resulting from catabolism can be used for biosynthesis again. The catabolic products which cannot be transformed by the organism, e.g., CO2,leave the body. Catabolism results in consumption of organic compounds and decrease in the body weight.Catabolism is, therefore,  also called destructive, or breakdown,  metabolism. Any product of catabolism is termed a catabolite.

In may be noted that not every catabolic reaction liberates energy. Some breakdown reactions that the cell performs to eliminate unwanted substances are actually endergonic.

Example: Breakdown of glycogen to carbon dioxide and water.

Anabolism and catabolism go on side _ by_ side. Anabolism normally outweighs catabolism. This enables the organism to grow and repair the wear and tear of its body. If catabolism outweighs anabolism, as happens in fasting, the organisms gradually becomes weak and finally dies.

Metabolism enables the cell to breakdown their old components and produce new ones in their place from the breakdown products. In fact, this is a regular feature of the cells. Thus, the material is never quite the same from time to time.

Animals are primarily catabolic organisms. They cannot synthesize organic compounds from simple inorganic compounds. In this respect, they differ from the green plants, which manufacture glucose from CO2 and H2O in the presence of sunlight , a process called photosynthesis. Animals require plants or other animals for food.

Energy Metabolism:

We need energy for growth, maintenance,  movement, reproduction, vital activities ( heart beat, peristalsis, mental work, etc.), biosynthesis, transmission of never impulse, active transport though cellular membranes,  and temperature regulation. It is supplied by carbohydrates, fats and proteins ( biomolecules) through enzymatic oxidation in the cells. The chemical reactions which liberate energy by enzymatic oxidation of food stuffs to CO2 and H2O in the tissue are referred to as the energy metabolism, or respiratory metabolism. The rate of O2 consumption is often regarded the rate of energy metabolism. This is not true for the anaerobic organisms. The latter have zero oxygen consumption but certainly not a zero  metabolic rate. The most important form of energy currency in living organisms is the bond energy in the chemical called adenosin triphosphate ( ATP).


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