The below mentioned article provides a study note on the Cellular Pool.
Biochemistry is the science dealing with chemicals and physicochemical reactions found in living organisms and their life processes. Chemicals or molecules present in the living organisms are known as biomolecules. The collection or sum total of different types of biomolecules, compounds and ions present in a cell is called the cellular pool.
The cellular pool has two phases, aqueous and non-aqueous. Aqueous phase contains chemicals dispersed in water forming either true solution (homogeneous, particle size 1 nm or less) or colloidal solution (heterogeneous, particle size 1-100 nm). Substances that form true solution are known as crystalloids while the ones that produce colloidal solution are called colloids.
Non-aqueous phase contains chemicals deposited in various structures like chromatin, cell membrane and cell wall. The chemical analysis of living and non-living matter, (earth is crust) reveal that both are made up of same types of elements but the relative abundance of С and H with respect to other elements is higher in any living organism than in non-living matter or earth’s crust (Table 9.1).
Biomolecules are of two types, inorganic and organic:
(i) Inorganic constituents of cellular pool are minerals, gases and water. Organic constituents are carbohydrates, lipids, amino acids, proteins, enzymes, nucleotides, nucleic acids, vitamins, etc.
(ii) Inorganic substances do not contain carbon along with hydrogen. Organic molecules possess carbon and hydrogen.
(iii) Minerals occur in the form of salts ions (table 9.2). Organic materials occur both in aqueous and non-aqueous phases.
Chemicals of the cellular pool are obtained from outside. Animal cells are bathed in an extracellular fluid having several chemicals.
However, the cells are able to maintain their specific cellular pool through selective intake of materials from outside, their metabolism inside the cell and selective elimination of specific chemicals. This is done through membranous covering of cell organelles and the plasma membrane. The membranes possess selective permeability and retentivity.
The chemicals of the cellular pool function as raw materials for carrying out various biochemical reactions of the cell organelles and the cell. Depending upon their molecular weight and solubility they fall in two categories: micro-molecules and macromolecules.
Micro-molecules or bio-micro-molecules are small sized simple chemicals that have low molecular weight (in-between 18 to 800 Daltons i.e., less than 1000 Daltons), higher solubility (if polar) and simple conformation.
These are found in acid soluble pool. Micro-molecules may be inorganic or organic and include water, gases, minerals, sugars, amino acids and nucleotides. Macromolecules or bio-macromolecules are large sized complex chemicals that have high molecular weight, (usually 10000 Daltons and above except lipids), low solubility and complex conformation. These are found in acid insoluble fraction.
They usually produce colloidal complex. They are always organic. Macromolecules generally belong to four classes of organic compounds— carbohydrates, lipids, proteins and nucleic acids.
Except lipids, other macromolecules are formed by polymerisation (condensation) of subunits called monomers. They produce chains of variable lengths. Because of their formation from monomers by polymerisation, these chains are also called polymers.
(a) Proteins are polymers of different amino acids. These amino acids are linked by peptide bond (CONH) formed by dehydration (polymerisation) between COOH group of one amino acid and NH2 group of next amino acid with the removal of H2O. (Fig. 9.1).
(b) In nucleic acids, the phosphate molecule links 3′ C of sugar of one nucleoside to the 5’C of sugar of next nucleoside, releasing 2 water molecules to form a 3′-5′ phosphodiester bond (O—HPO2—O; Fig. 9.3).
(c) In polysaccharides, the monosaccharide’s are linked by glycosidic bond (C-O-C) formed by dehydration between two carbon atoms of two adjacent monosaccharide’s (Fig. 9.2).
Large sized macromolecules assume a three-dimensional shape which enables them to function as structural components, nutrient stores, store-house of genetic information, energy sources, molecular messengers, enzymes, etc.
Lipids are considered to be macromolecules, though they have molecular weight less than 800 Daltons. Actually lipids are not water soluble. They get separated in acid insoluble fraction along with other macromolecules. Otherwise lipids are not strictly macromolecules. The average composition of living cell is water 70-90%, proteins 10-15%; carbohydrates 3%; lipids 2%; Nucleic acids 5-7%, ions 1%.