Biomolecules notes

Biomolecules are the chemical substances present in living cells that build structures, store energy, carry genetic information and catalyse reactions. NCERT classifies them by chemical nature, molecular size and biological role. In this chapter, you study inorganic elements, micromolecules like sugars, amino acids and nucleotides, and macromolecules like polysaccharides, proteins and nucleic acids. Lipids are special because they are acid-insoluble but not true polymers. Enzymes are mostly proteins that lower activation energy and make life possible at body temperature. Metabolism connects all biomolecules through anabolic and catabolic pathways, maintaining the living state as a dynamic, non-equilibrium condition.

Chemical analysis of living tissue shows that cells contain inorganic ions, water, minerals and organic compounds. The major elements in living organisms are carbon, hydrogen, oxygen, nitrogen, phosphorus and sulphur, with many trace elements also required. Biomolecules are broadly divided into micromolecules and macromolecules based on molecular size and solubility in trichloroacetic acid. Primary metabolites are directly involved in growth, development and reproduction, while secondary metabolites such as alkaloids, pigments and toxins often help in defense, attraction or ecological interactions. NCERT highlights that living and non-living matter contain the same elements, but living systems show complex organization and metabolism.

Carbohydrates are polyhydroxy aldehydes or ketones and their derivatives. Monosaccharides such as glucose and fructose are single sugar units; disaccharides such as sucrose, lactose and maltose contain two monosaccharides joined by glycosidic bonds; polysaccharides such as starch, glycogen and cellulose are large storage or structural molecules. Lipids are generally water-insoluble substances soluble in organic solvents. Simple lipids include fats and oils made of fatty acids and glycerol, while compound lipids such as phospholipids contain additional groups. Carbohydrates provide quick energy and structural support, while lipids store concentrated energy, form membranes, provide insulation and act as signaling molecules.

Proteins are polymers of amino acids joined by peptide bonds. Each amino acid has an amino group, carboxyl group, hydrogen atom and variable R group attached to a central carbon. The R group determines chemical nature, making amino acids acidic, basic, neutral, polar or non-polar. Protein structure is studied at four levels: primary sequence, secondary folding such as alpha helix and beta sheet, tertiary three-dimensional shape and quaternary arrangement of multiple polypeptide chains. Proteins perform diverse roles as enzymes, hormones, transporters, receptors, antibodies, structural fibers and contractile elements. For NEET, peptide bond formation, amino acid structure and protein levels are especially important.

Nucleic acids are polymers of nucleotides. Each nucleotide contains a nitrogenous base, pentose sugar and phosphate group. DNA usually contains deoxyribose sugar and bases adenine, guanine, cytosine and thymine, while RNA contains ribose and uracil instead of thymine. DNA is generally double-stranded and stores hereditary information, whereas RNA is usually single-stranded and helps express genetic information. The backbone is formed by phosphodiester bonds between sugar and phosphate groups, while complementary bases pair through hydrogen bonds. Major types of RNA include mRNA, tRNA and rRNA. NEET frequently asks nucleotide components, DNA-RNA differences, base pairing and RNA functions.

Enzymes are biological catalysts that accelerate biochemical reactions without being consumed. Most enzymes are proteins, though some RNA molecules act as ribozymes. Enzymes possess active sites where substrates bind to form an enzyme-substrate complex. They lower activation energy, making reactions fast enough to sustain life at normal temperatures. Enzyme activity is influenced by temperature, pH, substrate concentration, inhibitors and cofactors. Cofactors may be metal ions, organic coenzymes or tightly bound prosthetic groups. Enzymes are classified into oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. For NEET, enzyme mechanism, active site, cofactors and factor graphs are high-yield.

Metabolism is the total sum of all biochemical reactions occurring in a living cell. These reactions are organized into metabolic pathways, where each step is catalysed by a specific enzyme. Catabolism breaks complex molecules into simpler ones and usually releases energy, as in respiration. Anabolism builds complex molecules from simpler units and requires energy, as in protein synthesis or glycogen formation. Metabolism maintains the living state, which is a dynamic, non-equilibrium condition with continuous energy flow. NCERT emphasizes that isolated metabolic reactions outside the body are not living; life arises from coordinated, regulated metabolism inside cellular organization.