Biomolecules Notes: Class 11 Biology Chapter 9
Class 11 Biology Chapter 9 Biomolecules covers the chemical composition of living tissues, structure and classification of carbohydrates, proteins, lipids, nucleic acids, and the concept of enzymes.
Overview of Topics & Subtopics (Click to Jump)
1. Biomacromolecules
Short Note:
• Carbohydrates: classified as monosaccharides (e.g., glucose), oligosaccharides (e.g., sucrose), and polysaccharides (e.g., starch, cellulose, glycogen) — primarily provide energy and structural support.
• Proteins: polymers of amino acids linked by peptide bonds; perform structural, enzymatic, transport, hormonal, and defence functions.
• Lipids: fats, oils, and phospholipids; primarily used for energy storage and forming cell membranes.
• Nucleic Acids: DNA and RNA, polymers of nucleotides, carry and express genetic information.
2. Structure of Proteins
Short Note:
• Protein structure is described at four levels: primary (linear sequence of amino acids), secondary (alpha helix or beta pleated sheet), tertiary (3D folding), and quaternary (arrangement of multiple polypeptide subunits).
3. Enzymes
Short Note:
• Enzymes are biological catalysts, mostly proteins, that speed up biochemical reactions without being consumed, by lowering the activation energy required.
• Enzyme activity is affected by factors such as temperature, pH, substrate concentration, and the presence of inhibitors or cofactors.
NCERT Textbook Exercise Questions
What are macromolecules? Give examples.
Answer: Macromolecules are large, complex organic molecules formed by the polymerisation of smaller repeating units (monomers), typically having a high molecular weight. Examples include polysaccharides (like starch and cellulose), proteins, and nucleic acids (DNA and RNA).
Explain the composition of a triglyceride (fat molecule).
Answer: A triglyceride (fat) consists of one molecule of glycerol esterified with three molecules of fatty acids, linked via ester bonds; the fatty acids may be saturated (no double bonds) or unsaturated (with one or more double bonds).
Describe the important properties of enzymes.
Answer: Enzymes are highly specific to their substrates, act as catalysts (increase reaction rate without being consumed), function optimally at a particular temperature and pH, can be regulated by activators/inhibitors, and many require non-protein components called cofactors (coenzymes or metal ions) for activity.
Explain the four levels of the organisation of proteins.
Answer: Primary structure: the linear sequence of amino acids in a polypeptide chain. Secondary structure: the local folding pattern, such as an alpha helix or beta pleated sheet, stabilised by hydrogen bonds. Tertiary structure: the overall three-dimensional folding of the polypeptide chain, giving the protein its functional shape. Quaternary structure: the arrangement of two or more polypeptide subunits into a single functional protein complex (e.g., haemoglobin).
