:- Written By Zahra Madraswala


Cell is a structural and functional unit of life. It can be simple or complex in a structure and have ability to perform diverse function. Any cell whether it is simple or complex comprises various molecule in it, this molecules forms cellular pool inside the cells. Molecules forming chemical pool can be organic [amino acids, peptides, lipids etc] and inorganic.

For finding about the chemical nature of cellular pool a basic experiment can be performed which includes following steps

  1. Experimental tissue such as piece of vegetable or liver in trichloroacetic acid is taken and grinding is performed.
  2. Slurry obtained will be filter using cotton,

There will be two fractions first one is acid soluble which is also known as filtrate.

Second fraction is retentate can also be known as acid insoluble pool.

Most of the organic substances are soluble in acid. These organic molecules are of low molecular weight that ranges from 18-800 Dalton. These molecules are also known as micro molecules. Inorganic molecules are absent in acid soluble pool.

Following molecules are abundant in acid soluble pool of tissue :-

  • Amino acids
  • Smaller peptides
  • Nucleotides
  • Monosaccharide
  • Disaccharides
  • Lipids


Amino acid are small organic molecules with one characteristic  property that they all poses carboxylic acid group and an amino group both linked to their alpha carbon the identity of this side is what differentiate  one amino acid from other.

Structure of Amino Acid

Cell use amino acid to build proteins polymers made up of amino acids  which are joins head to tail in a long chain that fold up in to a 3 dimensional structure that is unique to each type of protein. The covalent bond between two adjacent amino acids in a protein chain is called a peptide bond. The chain of amino acid is known as polypeptide.

Like sugars all amino acids [except glycine] exist as optical isomer in a D and L form. But only L forms are found in proteins [although the D amino acids occur as a part of bacterial cell wall in some antibiotics.]

Twenty types of amino acids are commonly found in proteins each with a different side chain attached to the alpha carbon atom. The same twenty amino acids are found in all proteins whether they hail from bacteria, plants or animal.

The chemical diversity that the 20 standard amino acids provide is very  important to the function of protein. 5 of the 20 amino acids have side chain that can form ion in a solution and can therefore carry a charge. The other is uncharged. Some of them are polar and hydrophilic while others are non polar and hydrophobic.


When 2 or more amino acids combine together they form peptide bonds peptide are those molecules which consist of 2- 50 amino acids hence they are having shorter length than proteins. There are several smaller peptides that play a vital role in maintaining tissues structure and function. One of them is collagen. Collagen is the structural protein mainly found in extracellular matrix. It is considered as a main component of connective tissue .Collagen has been abundantly found in cornea blood vessels and in dentin of the teeth.

Creatine is another smaller peptide which facilities recycling of ATP primarily in the muscle and brain tissues. Its recycling is done by donating phosphate group to ADP. Hence it can be considered as vital peptide in cellular energy metabolism.


Nucleotides can act as short-term carriers of chemical energy.  ATP participates in the transfer of energy in varieties of metabolic reactions. ATP is formed through reactions that are driven by the energy released by the breakdown of foodstuffs. Its three phosphates are linked in series by two phosphoanhydride bonds. Rupture of these phosphate bonds releases large amounts of useful energy. The terminal phosphate group in particular is frequently split off by hydrolysis. In many situations, transfer of this phosphate to other molecules releases energy that drives energy-requiring biosynthetic reactions. Other nucleotide derivatives serve as carriers for the transfer of other chemical groups.


Nucleotides also have a fundamental role in the storage and retrieval of biological information. They serve as building blocks for the construction of nucleic acids—long polymers in which nucleotide subunits are linked by the formation of covalent phosphodiester bonds between the phosphate group attached to the sugar of one nucleotide and a hydroxyl group on the sugar of the next nucleotide.

The linear sequence of nucleotides in a DNA or an RNA molecule encodes genetic information. The two nucleic acids, however, have different roles in the cell. DNA, with its more stable, hydrogen-bonded helices, acts as a long-term repository for hereditary information, while single-stranded RNA is usually a more transient carrier of molecular instructions.


The simplest sugars—the monosaccharides—are compounds with the general formula (CH2O)n, where n can be 3, 4, 5, or 6. Sugars, and the larger molecules made from them, are also called carbohydrates because of this simple formula. Glucose, for example, has the formula C6H12O6 . The formula, however, does not fully define the molecule: the same set of carbons, hydrogen, and oxygen can be joined together by covalent bonds in a variety of ways, creating structures with different shapes. Thus glucose can be converted into a different sugar—mannose or galactose—simply by switching the orientations of specific –OH groups relative to the rest of the molecule.

The monosaccharide glucose has a key role in providing energy to the cell. It can be further broken down to smaller molecules in a series of reactions, releasing energy that the cell can use to do useful work. Cells use simple polysaccharides composed only of glucose units—principally glycogen in animals and starch in plants—as long-term stores of glucose, held in reserve for energy production. Sugars do not function exclusively in the production and storage of energy. Plant uses sucrose in transportation as it is non reducing form of sugar. They are also used, for example, to make mechanical supports. The most abundant organic molecule on Earth—the cellulose that forms plant cell walls—is a polysaccharide of glucose.


Monosaccharides can be linked by covalent bonds—called glycosidic bonds—to form larger carbohydrates. Two monosaccharides linked together make a disaccharide, such as sucrose, which is composed of glucose and a fructose unit. Sucrose has a key role in transportation through phloem. Unlike glucose sucrose lack reducing ends hence cannot react with other molecules during translocation.

Figure depicting :- Disaccharides can be formed by linkage of two monosaccharides through glycosidic bond.


Lipids are chemically diverse group of organic compound can be  defined as molecules that are insoluble or poorly soluble  in water but soluble in fat and organic solvents such as benzene. They typically contain long hydrocarbon chains in their due that they are hydrophobic in nature. Long chain of hydrocarbon is present in the fatty acids and multiple linked aromatic rings, is present in the steroids.

FIGURE DEPICTING :- the structure of palmitic acid [(A) Structural formula, (B) Ball and-stick model. (C) Space-filling model]

Fatty acids serve as a concentrated food reserve in cells, they can be broken down to produce about six times as much usable energy, as glucose. Fatty acids are stored in the cytoplasm of many cells in the form of fat droplets composed of triacylglycerol molecules—compounds made of three fatty acid chains covalently joined to a glycerol molecule. When a cell needs energy, the fatty acid chains can be released from triacylglycerols and broken down into two-carbon units. These two-carbon units are identical to those derived from the breakdown of glucose.

The most unique function of fatty acids is in the formation of the lipid bilayer, which is the basis for all cell membranes. These thin sheets, which enclose all cells and surround their internal organelles, are composed largely of phospholipids.

Other then general functions lipids is also present in different substances such as pigments, hormones, cofactors, signaling molecules and bile salts.


Cell is tiny structure which is not even visible by naked eyes. This microscopic structure performs several functions which makes life on earth to be possible. Cell contains diverse molecule that co-ordinately works together and allow cell to be functional and structural unit of life.



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