Cell Structure and Function: Molecules of the Cell and Biomolecules (For CBSE, ICSE, IAS, NET, NRA 2022)

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The cell and its organelles are made of organic chemicals such as proteins, carbohydrates, nucleic acid and fats are termed biomolecules. Inorganic molecules such as water and minerals are also present in the cell.


Water with unique physical and chemical properties has made life possible on earth. It is a major constituent of protoplasm and medium in which many metabolic reactions occur. It is universal solvent in which most substances remain dissolved and responsible for turgidity of cells.

Elements Necessary for Life

Hydrogen, Carbon, Oxygen, Nitrogen, Calcium, Potassium, Sodium, Magnesium, Phosphorous, Sulphur, Chlorine, Iron, Boron, Silicon, Manganese, Copper, Zinc, Cobalt and Molybdenum.

Functions: Ca is plant cell wall (C, H, O, and N as organic compounds) , Act as major cations (Na, K) and anions (Cl) in most physiological process, As cofactor of enzymes participate in most of the biochemical reaction of a cell (Fe, Cu, Mo, Zn, and B) , Involved in energy transfer reactions (P in ATP) . Green pigment chlorophyll in plants has magnesium in the center.


Image Showing Different Biomolecules
Composed of C, H and O.Most abundant organic substance present in nature in the form of cellulose in plant cell wall.
Simple six carbon sugar (glucose) is called a monosaccharide.In both plants and animals, it is used as a source of energy (sugar) .
Two molecules or units join together to form disaccharide (sucrose) .An important storage form in plants is starch and in animals it is glycogen.
More than ten units՚ monosaccharides join in a chain to form a polysaccharide e. g. starch and cellulose.Present in nucleic acids as five carbon sugar (Ribose) .
Amino acid
Basic amino acid structure shows that the central carbon atom is attached with an amino group (-Nh2) , a carboxylic acid group (-COOH) , one hydrogen and one side group (R) .Plants have the ability to utilize inorganic nitrogen and synthesize amino acid.
There are 20 different side groups which give 20 different amino acids.In animals՚ principal source of amino acid is the plant or animals that it consumers in its diet (pulses are rich in protein) .
Composed of C, H, O and N.Structurally protein form integral part of the membranes.
Amino acids join together by peptide bonds to form protein molecules.Functionally in the form of enzymes they play a vital role in metabolic reactions.
20 different amino acids make numerous simple and complex proteins.Synthesis of DNA is regulated by protein.
Based on the complexity of structure they can have primary, secondary, tertiary and quaternary structures. When proteins exist with other molecules they are known as conjugated proteins e. g. glycoprotein, lipoprotein, chromoprotein etc.Proteins are so important that nucleic acids directly regulate protein synthesis.
Nucleic Acids
They are two types: DNA (Deoxyribose nucleic acid) and RNA (Ribonucleic acid) . DNA has one oxygen less in its sugar molecule.DNA is the main genetic material for almost all organisms except certain viruses.
They are long chain polymers composed of units called nucleotides. Each nucleotide has pentose sugar, nitrogen base and phosphate group.RNA molecules are involved in formation transfer and protein synthesis.
Composed of C, H, O, amount of oxygen is very less.Due to their low oxygen content, they store and release more energy during oxidation.
They are synthesized from fatty acids and glycerol. Simple lipids are called glycerides.Molecules of fat can yield twice as much energy as from carbohydrates.
Fats can be saturated or unsaturated and solid at room temperature; those that remain liquid at room temperature are called oils.Phospholipids are important component of cell membrane.
Vitamins are organic compounds required in the diet of animals for their healthy growth.Vitamins (from plant) are essential nutrients in animals՚ diet as animals cannot synthesize such compounds.
Vitamins are classified according to their solubility; water soluble vitamin B and ascorbic acid and fat-soluble vitamins (A, D, E, and K) .Their deficiency causes various diseases in animal, like deficiency of vitamin B causes beriberi and that of vitamin C causes scurvy.
Plants have the ability to synthesize vitamins from CO2, NH3, and H2S.Vitamin A present in carotene pigment of carrot. Vitamin D can be produced by man with the help of sunlight. Vitamin K produced by bacteria in human intestine.
Hormones are specific organic substances effective in low concentrations, synthesized by cells in one part of the organism and then transported to another part of the organism, where it produces characteristic physiological responses.In animals՚ hormones (proteins, peptides or steroids) are produced in glands called endocrine glands which control all the biochemical activities of the organism. In plants hormones (growth hormones) are generally produced in metabolically active cells and control the vegetative and reproductive growth of the entire plant.
Alkaloids are complex organic compounds made of C, H, O and N and alkaloids in plants are produced from amino acids.The active principles of drugs from medicinal plants are generally alkaloids e. g. Quinine from cinchona plant. Ephedrine from Ephedra. Morphine from poppy plants.
These are fat soluble lipid compounds synthesized from cholesterol. They are produced by the reproductive organs like ovaries, testes and placenta and also by adrenal glands. They include testosterone, estrogen, cortisol etc.
Image Showing Different Biomolecules

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