Molecules of Cell

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

Water

Water with unique physical and chemical properties has made life possible on the earth. It is a major constituent of protoplasm. It is a medium in which all the metabolic reactions occur. It is a universal solvent in which most substances remain dissolved sparingly or completely. It is 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, Molybdenum, Iodine

Carbohydrate

Structure

  • Composed of C, H and O
  • Simple six carbon sugar (glucose) is called a monosaccharide.
  • Two molecules or units join together to form disaccharide (sucrose).
  • More than ten units of monosaccharides join in a chain to form a polysaccharide. For example, starch and cellulose.

Functions

  • Most abundant organic substance present in nature which occurs in the form of cellulo in plant cell wall.
  • In both plants and animals it is used as a source of energy (sugar).
  • An important storage form in plants is starch and in animals it is glycogen.
  • Present in nucleic acids as five carbon sugar (Ribose in RNA, and deoxyribose in DNA).

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). There are 20 different side groups which give 20 different amino acids.

Plants have the ability to utilize inorganic nitrogen and synthesize amino acid. In an animal, principal source of amino acids is provided by the plants or animals that it consumes in its diet (pulses are rich in protein).

Proteins

Proteins are composed of C, H, O and N. Amino acids join together by peptide bonds to form protein molecules. Twenty different amino acids make numerous simple and complex proteins.

Based on the complexity of structure the proteins can have primary, secondary, tertiary and quaternary structures. When proteins exist with other molecules they are known as conjugated proteins. For example, glycoprotein, lipoprotein and chromoprotein.

Structurally, proteins form integral part of the membranes. Functionally in the form of enzymes they play a vital role in metabolic reactions. Synthesis of DNA is regulated by proteins (enzymes). Proteins are so important that nucleic acids directly regulate protein synthesis.

Nucleic Acids

They are of two types: Deoxyribose nucleic acid (DNA) and Ribose nucleic acid (RNA).

They are long chain polymers composed of units called nucleotides. Each nucleotide has pentose sugar, nitrogen base and phosphate group. DNA has one oxygen less in its sugar molecule.

DNA is the main genetic material for almost all organisms except certain viruses. RNA molecules are involved in information transfer and protein synthesis. RNA acts as genetic material in some viruses like TMV (Tobacco Mosaic Virus).

Lipids

Lipids are composed of C, H, O. Amount of oxygen is very less. They are synthesized from fatty acids and glycerol. Simple lipids are called glycerides. 

Fats can be saturated or unsaturated. Fats are solid at room temperature, those that remain liquid at room temperature are called oils.

Due to their low oxygen content, and higher number of C-H bonds they store higher amount of energy and release more energy during their oxidation. A molecule of fat can yield twice as much energy as from carbohydrate.

Vitamins

Vitamins are organic compounds required in the diet of animals for their healthy growth. Vitamins are classified according to their solubility into two groups: water soluble and fat soluble. Plants have the ability to synthesize vitamins from CO2, NH3 and H2S.

Vitamins (from plant) are essential nutrients in animals diet as animals can not synthesize such compounds. Their deficiency causes various diseases.

Hormones

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 are produced in ductless glands called endocrine glands which control all the biochemical activities of the organism. In animals hormones may be proteins, peptides or steroids.

In plants hormones (growth regulators) are generally produced in metabolically active cells and control the vegetative and reproductive growth of the entire plant. Proteinaceous hormones are not found in plants.

Alkaloids

Alkaloids are complex organic compounds made of C, H, O and N. Alkaloids in plants are produced from amino acids. The active principles of drugs from medicinal plants are generally alkaloids.

Steroids

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, and cortisol.

Most of the steroids act as life-saving drugs, and others act as hormones which are effective in performing specific functions in specific organs of animal body.