Summary

  • Although there is a bewildering diversity of living organisms, their chemical composition and metabolic reactions appear to be remarkably similar.
  • The elemental composition of living tissues and non-living matter appear also to be similar when analysed qualitatively. However, a closer examination reveals that the relative abundance of carbon, hydrogen and oxygen is higher in living systems when compared to inanimate matter.
  • The most abundant chemical in living organisms is water. There are thousands of small molecular weight biomolecules.
  • Amino acids, monosaccharide and disaccharide sugars, fatty acids, glycerol, nucleotides, nucleosides and nitrogen bases are some of the organic compounds seen in living organisms.
  • There are 21 types of amino acids and 5 types of nucleotides. Fats and oils are glycerides in which fatty acids are esterified to glycerol.
  • Phospholipids contain, in addition, a phosphorylated nitrogenous compound. Only three types of macromolecules, i.e., proteins, nucleic acids and polysaccharides are found in living systems.
  • Lipids, because of their association with membranes separate in the macromolecular fraction. Biomacromolecules are polymers. They are made of building blocks which are different. Proteins are heteropolymers made of amino acids.
  • Nucleic acids (RNA and DNA) are composed of nucleotides. Biomacromolecules have a hierarchy of structures – primary, secondary, tertiary and quaternary.
  • Nucleic acids serve as genetic material. Polysaccharides are components of cell wall in plants, fungi and also of the exoskeleton of arthropods.
  • They also are storage forms of energy (e.g., starch and glycogen). Proteins serve a variety of cellular functions. Many of them are enzymes, some are antibodies, some are receptors, some are hormones and some others are structural proteins.
  • Collagen is the most abundant protein in animal world and Ribulose bisphosphate Carboxylase-Oxygenase (RUBISCO) is the most abundant protein in the whole of the biosphere. Enzymes are proteins which catalyse biochemical reactions in the cells.
  • Ribozymes are nucleic acids with catalytic power. Proteinaceous enzymes exhibit substrate specificity, require optimum temperature and pH for maximal activity.
  • They are denatured at high temperatures. Enzymes lower activation energy of reactions and enhance greatly the rate of the reactions.
  • Nucleic acids carry hereditary information and are passed on from parental generation to progeny.

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