What are the Biomolecules?

Biomolecules are the molecules that are synthesized by living organisms. These are the  molecules that are involved in the maintenance and metabolic processes of living organisms. These include vitamins,  lipids,  carbohydrates, amino acids, proteins,  etc. All of these compounds are organic in nature .These molecules are found in both aqueous and non __ aqueous phase. 


There is one feature  common to all those compound found in the acid soluble in the acid soluble pool. They have molecular weights ranging  from 18 to around 800 daltons ( Da) approximately. 

The acid insoluble  fraction has only  four types of organic compounds, i.e.   proteins , nucleic acids, polysaccharides  and lipids. These classes of compounds with the  exception of lipids have molecular weights in the range of ten thousand  daltons and above. For this very reason, biomolecules, i.e., chemical compounds found in living organisms are of two types.One, those that have molecular weights less than one thousand  Dalton and are usually  referred  to as micromolecules or simply biomolecules while those which are found in the acid insoluble  fraction are called  macromolecules or biomacromolecules.

  The molecules in the molecular fraction with the exception  of  lipids  are polymeric substances. Then why do lipids whose molecular weights do not exceed  800 Da, come under acid insoluble  fraction, i.e., macromolecular fraction? Lipids are indeed small  molecular weight  compounds and are present  not only as such but also arranged into structure  like membrane and other membranes. When we grind a tissue, we are disrupting  the cell structure . Cell membrane and other membranes  are broken into pieces,  and form vesicles,  which are not water_ soluble. Therefore , these membrane fragments in the form of vesicles  get separated  along with the acid insoluble  pool and hence in  the   macromolecular fraction .lipids are not strictly macromolecular

Average Composition  of Cells

Component       :  % of the total cellular  mass

Water                  :  70__90

Proteins               : 10__ 15

Carbohydrates    : 3

Lipids                   : 2

Nucleic acids      :  5__ 7

Ions                       :   1

One of the greatest  discoveries ever made was the observation that all these biomolecules have a turn over. This means  that they they  are constantly  being changed into some other biomolecules and also made from some other biomolecules. 

The living State

The most important fact of biological  systems is that all living  organisms  exist in a steady state characterized by concentration of each of these biomolecules. These biomolecules are in a metabolic fluc. Any chemical  or physical  process moves spontaneously  to equilibrium. The steady state is a non_ equilibrium   state. One should remember  from physics that systems  at equilibrium  could not perform  work. As living organisms work continuously , they cannot afford to reach equilibrium .Hence the living  state is non_ equilibrium steady  to be able to perform  work; living  process is a constant  effort  to prevent  falling  into equilibrium. This is achieved  by energy  input.Metabolis provides a mechanism for the production  of energy. Hence the living  state and metabolism are synonymous. Without  metabolism  there cannot be a living state.

■ Carbohydrates: Carbohydrates are the key source of energy for most of the living organisms. In organisms, the normally occur as monosacchride or  polysaccharide compounds. Monosacchrides are simple sugars, polysaccharides are complex forms of sugar used for storage or structural purposes. 

■  Lipids: Lipids are large and diverse group of compounds that are soluble in non__ polar organic solvents like alcohol. These compounds include fats, oils, waxes and sterols. They are extensively found in cell membranes and they act as energy storage and signaling molecules. 

Proteins:These are large molecules made up of one or more chains of amino acids in specific order. Almost 43 per cent of dry weight of human bodies is due to proteins. 

Nucleic Acids:  Nucleic  acids are chains of  nucleotides. Nucleotides are basic essential components for the existence of the known human life. These nucleic acids can be DNA or RNA.

Chemicals of living and non living systems :

If we perform elemental analysis of a  plant tissue, animal tissues, microbial past ( living matter) and of a piece of earth's crust ( non__ living matter), we find that all living and non__ living system are made up of same chemicals, i.e., elements ( e.g., carbon, hydrogen, oxygen and several others) and compounds,  and their chemicals follow the same set of rules. Close examination,  however, has indicated that most living organisms have relatively high abundance of carbon and hydrogen than in earth's crust .Further, living organisms are composed mainly of water whereas the non__ living systems may or may not contain water.

Biological Molecules ( Biomolecules): 

Every cell is composed of a variety of molecules and molecular aggregates. The molecules, found in the cells of organisms are called biological molecules, or biomolecules. 

Biochemistry: The study of the molecules ( chemicals) of the living organisms and of the chemicals changes occurring in them is called biochemistry ¹.It facilitates our understanding of physiology, that is, working of biological systems. A specialist in biochemistry is known as a biochemist.

 A: Chemical Elements of life ( Biological Elements): 

What is an Element? 

The chemical elements are substances which cannot be broken up by ordinary chemical processes into simpler ubstances. Each element has a unique set 1of properties. Twenty __ five elemenhave been identified in the cells and extracellular fluids. These elements are compatible with life because of their special properties. They are called biological elements,or bioelements. 

     List of Bioelements: The biological elements include oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, chlorine, sulphur, potassium, sodium, magnesium, iodine, iron, copper, cobalt, zinc, silicon, manganese, fluorine, vanadium, molybdenum, boron, chromium, tin and aluminium. 

● Classification of Bioelements:

The Bioelements may be arranged in three groups:

1): Principal ( Major) Elements: This group include the first four elements given in the above list, viz., oxygen, carbon, hydrogen and nitrogen. They are so named because they alone constitute about 95% of the weight of the cell contents. They include only nonmetals. The biological importance of the principal elements is mainly due to their ability to form more stable covalent bonds than any other elements with the same valencies that these elements have ( 2,4,1,3 respectively).

2): Minor Elements: This group includes the next nine elements mentioned in the above list. They form a little less than the remaining 5% of the weight of the cell contents. They include both metals and nonmetals. The metal elements are calcium,  potassium, sodium, magnesium and iron. They form less than  3% of the cell contents. The nonmetal elements are phosphorus, chlorine, sulphur and iodine.  They form less than 2% of the cellular constituents.

        Essential Elements: The above 13 elements occur in almost all types of cells and are called the essential elements. 

3): Trace Elements: This groups includes the remaining 12 elements given in the above list. They form less than 1% of the weight of the cell contents, and are found in particular types of cells only. They also include both metals and nonmetals. The nonmetalic trace elements are silicon, fluorine and boron. Others are metal elements. 

B): Compounds of Life ( Biological Compounds): 

What is a Compound? 

The elements of life are rarely found as such in the cells. They generally occur as compounds and ions. A compound is a substance composed of atoms of two or more different elements, in specific proportions, and with  a specific pattern of bonds. For instance,  a water molecule formed of oxygen and hydrogen atoms is a compound. Properties of a compound differ from those of its component elements.  A molecule of a compound is the smallest unit which has all the properties of the compound. The ironically bonded compounds are said to consist of ions instead of molecules. An ion is an atom that carries a change due to loss or gain of electrons.

● Kind of Compounds
The compounds are of two kinds: inorganic and organic 

(i) Inorganic Compounds: The inorganic compounds usually lack the element carbon. They have relatively small molecules with simple structure and low molecular weights. They include water, mineral salts and ions, and gases.

( ii)  Organic Compounds: The organic compounds contain the elements carbon. The carbon atoms are bonded to form a string ( chain) or ring which serves as a " skeleton " for organic molecule. The most of their carbon atoms are also bonded to one or more hydrogen atoms. The organic compounds are chiefly formed by living organisms, hence their name. They have large molecules with complex structure and high molecular weight. They include carbohydrates, lipids, proteins, nucleotides, nucleic acids, and vitamins.

      The variation in carbon skeleton is the basis of all biological diversity at the molecular level.
       To obtain organic compounds, one has to perform a chemical analysis. Let us take any living tissue ( say  a piece of liver or a piece vegetable etc) grind it in trichloroacetic acid ( C13CCOOH) using a mortar and a pestle to obtain a thick slurry. Now filter it through a cheesecloth or cotton. We would obtain filtrate ( acid __ soluble pool) and the relentate ( acid __ insoluble  fraction). Scientists have been able to extract large number of organic compounds in the acid_ soluble pool by using different separation techniques. In other words, one can isolate and purify a compound.  Later, analytical techniques help us to obtain molecular formula and the probable structure of the compund. 

      All the inorganic and organic compounds present in the cells are the example of biological molecules or biomolecules. The percentages of the various biological compounds present in the cells .

Cellular Pool

The aggregation of the various kinds of biomolecules in a cell is referred to as the cellular pool.

Composition: The  cellular  pool comprises over 5000 chemicals. These included both inorganic and organic molecules. The inorganic molecules generally occur in the aqueous phase. The organic molecules occur in both aqueous and nonaqueous phases.

        Maintenance of Pool's Composition: The cell maintains the composition of its pool by taking up and eliminating specific molecules through its semipermeable plasma membrane. This steady state within the cell is essential for its survival. The cellular pool provides all the necessary materials for the structure and functions of the cells. 

     The composition of the cellular pool in animal cell is quite different from that of the extracellular fluid. The difference is maintained by the cell membrane through its selective permeability. 


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