Biomolecules

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Biomolecules NEET PDF Notes | Biomolecules PYQs

Analysis of Chemical Composition

Acid Soluble vs. Insoluble Pool

Living tissues are ground in trichloroacetic acid (Cl3CCOOH) to form a slurry, then strained to separate fractions.

  • Acid Soluble Pool (Filtrate): Contains biomicroolecules (molecular weight 18–800 Da) like amino acids, sugars, nucleotides, and inorganic ions.
  • Acid Insoluble Pool (Retentate): Contains biomacromolecules (weight >10,000 Da) like proteins, nucleic acids, and polysaccharides.
  • Exception: Lipids have a molecular weight <800 Da but are found in the acid-insoluble pool because cell membrane fragments form water-insoluble vesicles during grinding NEET 2024 Re NEET 2022 AIPMT 2002.
  • Ash Analysis: Used to study inorganic elements. The tissue is burnt to remove carbon compounds as CO2 and water vapor; the remaining ash contains calcium, magnesium, etc.

Elemental Composition

  • Oxygen is the most abundant element in the human body (65%) AIPMT 1994 AIPMT 2011.
  • Order of abundance in humans: O > C > H > N.
  • Four elements make up 99% of living systems: C, H, O, N AIPMT 1994.
  • Water is the most abundant chemical compound in living organisms (70-90%) AIPMT 1992.

Metabolites

Primary & Secondary Metabolites

  • Primary Metabolites: Have identifiable functions and play known roles in normal physiological processes (e.g., amino acids, sugars, fats).
  • Secondary Metabolites: Functions in the host organism are not fully understood, but many are useful for human welfare (e.g., drugs, spices, pigments).
Category Examples PYQ Relevance
Pigments Carotenoids, Anthocyanins NEET 2023 Manipur NEET 2022 Re
Alkaloids Morphine, Codeine NEET 2021 NEET 2023 Manipur
Terpenoids Monoterpenes, Diterpenes NEET 2023 Manipur
Essential Oils Lemon grass oil
Toxins Abrin, Ricin NEET 2021 NEET 2023 Manipur NEET 2020
Lectins Concanavalin A NEET 2021 NEET 2023 Manipur NEET 2019
Drugs Vinblastin, Curcumin NEET 2021 AIPMT 2007
Polymeric Rubber, Gums, Cellulose NEET 2021

Biomacromolecules

Carbohydrates (Saccharides)

Formula is generally Cx(H2O)y. They are polyhydroxy aldehydes or ketones.

  • Monosaccharides: Cannot be further hydrolyzed. Include glucose (blood sugar/dextrose), fructose (sweetest, fruit sugar, laevulose), galactose (brain sugar). All monosaccharides are reducing sugars AIPMT 2002.
  • Oligosaccharides (2-10 units): Linked by glycosidic bonds formed via dehydration synthesis NEET 2024 NEET 2023 Manipur NEET 2021.
    • Maltose: Glucose + Glucose (α 1-4 linkage). Reducing.
    • Lactose: Glucose + Galactose (α 1-4 linkage) AIPMT 1998. Reducing.
    • Sucrose: Glucose + Fructose (1-2 linkage). Non-reducing sugar NEET 2014.
  • Polysaccharides (Glycans): Non-reducing, insoluble in water.
    • Cellulose: Unbranched β 1-4 polymer of D-glucose. Does not contain complex helices and cannot hold iodine (does not give blue color) NEET 2023. Major component of plant cell walls and paper pulp AIPMT 2005.
    • Starch: Plant storage. Amylose (unbranched, α 1-4) and Amylopectin (branched, α 1-6). Gives blue color with iodine.
    • Glycogen: Animal starch stored in liver and muscles. Highly branched polymer of α-D-glucose AIPMT 1993 NEET 2024 AIPMT 2001 AIPMT 1995.
    • Chitin: Homopolymer of N-acetyl-D-glucosamine (β 1-4 linkage). Forms exoskeleton of arthropods and fungal cell walls NEET 2022 NEET 2015 Re NEET 2020.
    • Inulin: Polymer of fructose NEET 2023 Manipur AIPMT 2001.

Lipids

  • Water-insoluble due to their hydrophobic nature AIPMT 2002 NEET 2022.
  • Simple Lipids: Esters of fatty acids with glycerol NEET 2016. Glycerol is trihydroxy propane NEET 2022 NEET 2020. They are linked by ester bonds NEET 2024.
  • Fatty Acids:
    • Saturated: No double bonds. E.g., Palmitic acid (16 carbons including carboxyl carbon) NEET 2022 Re AIPMT 2012. Arachidic acid (20 carbons).
    • Unsaturated: Contain one or more C=C double bonds NEET 2023 Manipur NEET 2021. E.g., Oleic acid, Arachidonic acid (20 carbons including carboxyl) NEET 2022 Re. Erucic acid is used to detect oil spoilage AIPMT 2001.
  • Compound Lipids: E.g., Phospholipids. Lecithin is a phosphorylated glyceride found in cell membranes NEET 2024 Re NEET 2024 NEET 2022 NEET 2020 AIPMT 2012. It is amphipathic.

Amino Acids & Proteins

  • Amino Acids: Substituted methanes with four groups (H, carboxyl, amino, and variable R group) on the α-carbon.
  • Exhibit ionizable properties (amphoteric) and can exist as Zwitterions at specific pH levels NEET 2024.
  • Types of Amino Acids:
    • Acidic: Glutamic acid, Aspartic acid.
    • Basic: Lysine, Arginine NEET 2020 AIPMT 2012.
    • Aromatic: Tyrosine, Phenylalanine, Tryptophan NEET 2020.
    • Sulphur-containing: Cysteine, Methionine NEET 2020 NEET 2016.
  • Proteins: Heteropolymers of amino acids linked by peptide bonds NEET 2024 NEET 2023 Manipur NEET 2021.
  • Most abundant protein in the animal world: Collagen NEET 2024 NEET 2020 AIPMT 2012 AIPMT 2001.
  • Most abundant protein in the biosphere: RuBisCO AIPMT 1999.
  • GLUT-4: Protein that enables glucose transport into cells (insulin-dependent) NEET 2024 NEET 2019.
  • Protein Structure:
    • Primary: Linear sequence of amino acids (peptide bonds). Left end = N-terminal (first AA), Right end = C-terminal (last AA) NEET 2024 Re NEET 2023 NEET 2022 Re.
    • Secondary: Local folding (α-helix, β-pleated sheet) stabilized by hydrogen bonds NEET 2024 Re AIPMT 1999.
    • Tertiary: 3D folding forming crevices (active sites); absolutely necessary for biological activity. Stabilized by H-bonds, disulphide bonds, hydrophobic, and electrostatic interactions NEET 2024 Re NEET 2016.
    • Quaternary: Assembly of multiple subunits. Adult human hemoglobin consists of 4 subunits (2 α and 2 β) NEET 2024 Re NEET 2023.

Nucleic Acids (DNA & RNA)

  • Polymers of nucleotides NEET 2023 Manipur AIPMT 1991.
  • Nucleotide: Consists of a nitrogenous base, pentose sugar, and phosphate group AIPMT 1991. Linked by phosphodiester bonds NEET 2024 NEET 2023 Manipur NEET 2021 NEET 2015 Re.
  • Nucleoside: Nitrogenous base + Sugar (e.g., Uridine, Guanosine, Adenosine) NEET 2024 Re AIPMT 2012 AIPMT 1992.
  • Nitrogenous Bases:
    • Purines: Adenine, Guanine (2 rings) NEET 2016 AIPMT 1996 AIPMT 1992.
    • Pyrimidines: Cytosine, Thymine, Uracil (1 ring) AIPMT 1992.
  • In RNA, Uracil replaces Thymine AIPMT 1992 AIPMT 1988.

Metabolism

  • Anabolic Pathways (Biosynthetic): Consume energy to build complex structures.
  • Catabolic Pathways: Release energy via breakdown (e.g., glucose to lactic acid).
  • The living state is a steady-state characterized by a non-equilibrium metabolic flux.

Enzymes

Properties & Mechanism

  • Enzymes lower the activation energy of a reaction AIPMT 2013 AIPMT 2000.
  • Transition State: The structure of the substrate during the reaction is transient and unstable AIPMT 2013.
  • Most enzymes are proteins, but some are nucleic acids called ribozymes NEET 2016.
  • Temperature & pH: Enzymes show highest activity at optimum values. Low temperature preserves enzymes in a temporarily inactive state, while high temperature denatures them NEET 2024 Re AIPMT 2010.
  • Substrate Concentration: Velocity rises until it reaches Vmax. Further substrate addition does not increase velocity because enzyme active sites are fully saturated NEET 2024 Re AIPMT 2010. Km is the substrate concentration at ½ Vmax AIPMT 2005.
  • Catalytic Cycle: Substrate binds to active site → induces shape change → chemical bonds break/form → product is released → free enzyme is ready to bind another substrate NEET 2024.

Classification of Enzymes

  • Oxidoreductases / Dehydrogenases: Catalyze oxidation-reduction.
  • Transferases: Catalyze transfer of a group between substrates.
  • Hydrolases: Catalyze hydrolysis of ester, ether, peptide, glycosidic bonds AIPMT 2002.
  • Lyases: Catalyze removal of groups by mechanisms other than hydrolysis, leaving double bonds NEET 2024 Re.
  • Isomerases: Interconversion of isomers.
  • Ligases: Catalyze linking together of 2 compounds (e.g., C-O, C-S, C-N, P-O bonds; not C-C breakdown) NEET 2024 Re.

Cofactors & Inhibition

  • Holoenzyme (active) = Apoenzyme (protein part) + Cofactor (non-protein part) NEET 2017.
  • Types of Cofactors:
    • Prosthetic Groups: Tightly bound to the apoenzyme. E.g., Haem is the prosthetic group for peroxidase and catalase (which breaks down H2O2) NEET 2022 Re NEET 2020.
    • Co-enzymes: Organic compounds; association is transient during catalysis. E.g., NAD and NADP contain the vitamin Niacin NEET 2019.
    • Metal Ions: Form coordination bonds. E.g., Zinc (Zn2+) is a cofactor for carboxypeptidase and carbonic anhydrase NEET 2024 AIPMT 2012.
  • Competitive Inhibition: The inhibitor closely resembles the substrate (structural analogue) and competes for the active site NEET 2024 Re AIPMT 2012.
  • E.g., Malonate inhibits Succinic Dehydrogenase (pathogenic bacteria control) NEET 2024 NEET 2023 NEET 2020 NEET 2014.
  • Reversible; Km increases, but Vmax remains unchanged NEET 2015.

Vitamins & Deficiency (High-Yield PYQ Specifics)

Note: Heavily tested via matching questions historically.

  • Vitamin C (Ascorbic Acid): Deficiency causes Scurvy AIPMT 1995.
  • Vitamin B1 (Thiamine): Deficiency causes Beri-Beri AIPMT 2004 AIPMT 1999.
  • Vitamin B3 (Niacin/Nicotinic acid): Deficiency causes Pellagra AIPMT 1994.
  • Vitamin B12 (Cyanocobalamin): Induces maturation of RBCs; deficiency causes pernicious anemia. Richest sources: Goat's liver, Spirulina AIPMT 2004 AIPMT 1998.
  • Vitamin A (Retinol): Fat-soluble; deficiency causes Night blindness/Xerophthalmia AIPMT 2004.
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