📝 Chapter Notes & Revision

Biomolecules

🏫 MP BoardClass 11Biology

📐 Formula & Cheat Sheet (English)

Quick Revision Notes: Class 11 Biology

Chapter: Biomolecules (जैव अणु)

### Introduction to Biomolecules

  • Biomolecules: All the carbon compounds that we get from living tissues can be called 'biomolecules'.
  • Metabolites:
    • Primary Metabolites: Identical in living tissues (e.g., amino acids, sugars).
    • Secondary Metabolites: Alkaloids, flavonoids, rubber, essential oils, antibiotics, pigments, scents, gums, spices (e.g., Morphine, Codeine, Anthocyanin).
  • Acid-insoluble fraction (Macromolecules): Biomolecules having molecular weights ranging from 10,000 Daltons (Da) and above (Proteins, Nucleic acids, Polysaccharides, Lipids).
  • Acid-soluble fraction (Micromolecules): Biomolecules with molecular weights ranging from 18 to around 800 Daltons (Amino acids, monosaccharides, nucleotides).

### Concept 1: Proteins (प्रोटीन)

Proteins are heteropolymers of amino acids. They are polypeptide chains.

  • Amino Acids: Organic compounds containing an amino group (-NH_2) and an acidic carboxyl group (-COOH) on the same carbon (alpha-carbon).

    • General Formula: R - CH(NH_2) - COOH
    • Zwitterionic Form: At a specific pH, amino acid exists as a dipolar ion carrying both positive and negative charges.

  • Classification based on R-group:

    • Acidic: Glutamic acid, Aspartic acid
    • Basic: Lysine, Arginine, Histidine
    • Neutral: Glycine, Alanine, Valine
    • Aromatic: Tyrosine, Phenylalanine, Tryptophan

  • Levels of Protein Structure:

    • Primary Structure: Linear sequence of amino acids joined by peptide bonds (-CO-NH-).
    • Secondary Structure: Folding of polypeptide chains into $\alpha$-helix or $\beta$-pleated sheets (stabilized by hydrogen bonds).
    • Tertiary Structure: 3D folding of a protein chain (vital for biological activity).
    • Quaternary Structure: Assembly of multiple polypeptide subunits (e.g., Hemoglobin has 4 subunits: $2\alpha$ and $2\beta$).

### Concept 2: Carbohydrates & Polysaccharides (कार्बोहाइड्रेट और पॉलीसैकराइड)

Carbohydrates are hydrates of carbon; polyhydroxy aldehydes or ketones.

  • Monosaccharides (Simple Sugars): Single unit of sugar. E.g., Glucose ($C_6H_{12}O_6$), Fructose, Ribose ($C_5H_{10}O_5$).

  • Oligosaccharides: 2 to 9 monosaccharide units joined by Glycosidic bonds.

    • Sucrose = Glucose + Fructose
    • Lactose = Glucose + Galactose
    • Maltose = Glucose + Glucose

  • Polysaccharides (Complex Carbohydrates): Long chains of monosaccharides.

    • Starch: Plant storage polysaccharide (gives blue-black color with iodine). Made of amylose and amylopectin.
    • Glycogen: Animal storage polysaccharide ("animal starch", stored in liver and muscles).
    • Cellulose: Plant cell wall component, homopolymer of glucose (gives no color with iodine).
    • Inulin: Polymer of fructose.
    • Chitin: Exoskeleton of arthropods, fungal cell walls (N-acetylglucosamine polymer).

### Concept 3: Lipids (लिपिड)

  • Lipids are water-insoluble, containing carbon, hydrogen, and oxygen, but the proportion of oxygen is very low compared to carbohydrates.
  • Simple Lipids (Fats): Esters of fatty acids with glycerol. Glycerol is trihydroxy propane (CH_2OH-CHOH-CH_2OH).
    • Fatty Acids: Have a carboxyl group attached to an R group (R-COOH).
      • Saturated Fatty Acids: No double bonds (e.g., Palmitic acid, Stearic acid). Usually solid at room temperature.
      • Unsaturated Fatty Acids: One or more double bonds (e.g., Oleic acid, Linoleic acid). Usually liquid at room temperature (Oils).
  • Phospholipids: Lipids containing a phosphate group (e.g., Lecithin), found in cell membranes.
  • Derived Lipids: Steroids (e.g., Cholesterol).

### Concept 4: Nucleic Acids (न्यूक्लिक अम्ल)

Polymers of nucleotides, responsible for genetic information storage and transfer.

  • Components of a Nucleotide:

    1. Nitrogenous Base:
      • Purines: Adenine (A), Guanine (G)
      • Pyrimidines: Cytosine (C), Thymine (T) [Uracil (U) in RNA instead of T]
    2. Pentose Sugar: Ribose (in RNA) or Deoxyribose (in DNA).
    3. Phosphate Group: Attached via phosphoester bond.

  • Nucleoside: Nitrogenous Base + Sugar

  • Nucleotide: Nitrogenous Base + Sugar + Phosphate Group

  • DNA Structure (Watson & Crick Model):

    • Double helix model.
    • Two polynucleotide chains anti-parallel to each other ($5' \rightarrow 3'$ and $3' \rightarrow 5'$).
    • Base pairing: $A = T$ (two hydrogen bonds), $G \equiv C$ (three hydrogen bonds).
    • Distance between base pairs = $0.34\text{ nm}$ ($3\text{ \AA}$).
    • Pitch of helix = $3.4\text{ nm}$ ($34\text{ \AA}$).

### Concept 5: Enzymes (एन्जाइम)

Enzymes are biocatalysts that accelerate biochemical reactions without being consumed. Almost all enzymes are proteins (except Ribozymes, which are catalytic RNAs).

  • Enzyme Structure:

    • Apoenzyme: Protein part of the enzyme.
    • Cofactor: Non-protein part essential for enzyme activity.
      1. prosthetic groups: Tightly bound organic compounds (e.g., Heme in peroxidase).
      2. Co-enzymes: Transiently bound organic compounds (e.g., NAD, NADP, Vitamins).
      3. Metal ions: Form coordination bonds with side chains (e.g., $Zn^{2+}$ is a cofactor for Carboxypeptidase).
    • Holoenzyme: Apoenzyme + Cofactor (Active enzyme).

  • Mechanism of Enzyme Action (Lock and Key / Induced Fit):

    1. Substrate binds to the active site of the enzyme, forming an Enzyme-Substrate complex (ES).
    2. Chemical bonds are broken/formed to transform substrate into product (EP).
    3. Enzyme releases the products and is free to bind another substrate molecule.

  • Factors Affecting Enzyme Activity:

    • Temperature & pH: Enzymes show highest activity at optimum temperature and pH. Activity declines at both high and low extremes.
    • Concentration of Substrate: Velocity of reaction increases with substrate concentration up to a maximum limit ($V_{max}$).
    • Inhibition:
      • Competitive Inhibitor: Resembles the substrate and binds to the active site, inhibiting the enzyme (e.g., Inhibition of succinic dehydrogenase by malonate).
      • Non-competitive Inhibitor: Binds to a site other than the active site (allosteric site) and changes the shape of the enzyme.

  • IUBMB Classification of Enzymes (6 Classes):

    1. Oxidoreductases / Dehydrogenases: Oxidation-Reduction reactions.
    2. Transferases: Transfer of a group between two substrates.
    3. Hydrolases: Hydrolysis of ester, ether, peptide, glycosidic bonds.
    4. Lyases: Removal of groups from substrates by mechanisms other than hydrolysis.
    5. Isomerases: Interconversion of optical, geometrical, or positional isomers.
    6. Ligases: Linking together of two compounds (e.g., DNA ligase).