Biomolecules - Premium NCERT NotesI. Chemical Composition of Living Organism
All living organisms are made up of same elements and compounds as found in non-living earth's crust, but in
different proportions. Carbon and Hydrogen are much higher in living tissues.
[i] Analysis Strategy: Living tissue + Tri-chloroacetic acid
(Cl3CCOOH) -> Grinding -> Filter -> Two fractions:
--> Acid Soluble Pool: Filterate (Micromolecules, Molecular weight 18-800 Dalton).
--> Acid Insoluble Pool: Retentate (Macromolecules, Molecular weight > 10,000 Dalton).
[!] EXCEPTION: Lipids have molecular weight < 800 Dalton (micromolecule) but
are found in the Insoluble Pool because they form water-insoluble vesicles
when tissues are ground.
II. Primary and Secondary Metabolites
Primary Metabolites: Have identifiable functions and play known roles in normal physiological
processes (e.g., sugars, amino acids).
Secondary Metabolites: Found in plant, fungal and microbial cells. Roles are not always clear (e.g.,
alkaloids, flavonoids, rubber, essential oils, antibiotics).
[Table] Important Secondary Metabolites:
--> Pigments: Carotenoids, Anthocyanins.
--> Alkaloids: Morphine, Codeine.
--> Terpenoids: Monoterpenes, Diterpenes.
--> Lectins: Concanavalin A.
--> Drugs: Vinblastin, Curcumin.
--> Polymeric: Rubber, Gums, Cellulose.
III. Proteins: The Building Blocks
Proteins are Heteropolymers of amino acids. They are linear chains linked by
Peptide Bonds.
- Amino Acids: Organic compounds with an amino group and an acidic group on the same carbon
(alpha-carbon).
- Essential vs Non-essential: Essential must be supplied through diet.
- Collagen: Most abundant protein in animal world.
- RuBisCO: Most abundant protein in the whole biosphere.
[!] Protein Structures:
--> Primary: Line sequence of amino acids (gives positional info).
--> Secondary: Alpha-helix (right-handed) and Beta-sheets.
--> Tertiary: 3D folding (essential for biological activities/enzymes).
--> Quaternary: Complex of multiple polypeptides (e.g., adult Hemoglobin has 2 alpha and 2 beta
subunits).
IV. Polysaccharides and Nucleic Acids
Polysaccharides: Long chains of sugars. Starch (plants), Glycogen (animals), Cellulose (cell walls).
Chitin is a complex polysaccharide (N-acetyl glucosamine) found in exoskeleton of arthropods.
Nucleic Acids: DNA and RNA. Polymers of Nucleotides. A nucleotide has 3 components:
Heterocyclic compound (Base), Monosaccharide (Sugar), and Phosphoric acid/Phosphate.
[Key] Nitrogenous Bases:
--> Purines: Adenine, Guanine.
--> Pyrimidines: Cytosine, Thymine (DNA), Uracil (RNA).
V. Enzymes: Biocatalysts
Almost all enzymes are proteins. They have an Active Site for substrate binding. They lower the Activation Energy of a reaction.
- Factors: Temperature, pH, and substrate concentration (Km value) affect activity.
- Inhibition: Competitive inhibitors (e.g., Malonate inhibits Succinate Dehydrogenase) resemble the
substrate.
- Classes: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases.
[!] Co-factors: Non-protein part required for activity.
--> Prosthetic Group: Tightly bound organic (e.g., Heme in peroxidase).
--> Co-enzyme: Transiently bound organic (e.g., NAD, NADP).
--> Metal Ions: Coordination bonds (e.g., Zinc for Carboxypeptidase).
[Q] Why are lipids found in the acid-insoluble pool despite
having a low molecular weight?
[A] Explanation:Lipids are strictly speaking not macromolecules. However, during tissue grinding, cell membranes (which
are rich in lipids) are broken into fragments. These fragments form water-insoluble vesicles
which are trapped in the retentate (acid-insoluble pool) along with true macromolecules.
[Q] Differentiate between a Prosthetic group and a
Co-enzyme.
[A] Explanation:A prosthetic group is an organic compound that is permanently and tightly bound to the apoenzyme
(e.g., Heme in peroxidase). A co-enzyme is an organic compound that is transiently associated
with the enzyme, typically during catalysis (e.g., NAD, NADP).
[Q] What happens to the rate of enzymatic reaction if the
temperature is increased significantly beyond the optimum?
[A] Explanation:High temperatures cause denaturation of the enzyme protein. Since the tertiary structure of the
protein is destroyed, the active site loses its specific shape and cannot bind with the substrate,
leading to a complete halt of the reaction.
[Q] Why is Cellulose called a structural polysaccharide
while Starch is a storage polysaccharide?
[A] Explanation:Cellulose consists of long, linear chains of glucose that provide rigid structural support to plant cell
walls. Starch forms helical secondary structures that can hold iodine and act as energy reserves for the
plant.
[Q] Explain the "Competitive Inhibition" with an
example.
[A] Explanation:In competitive inhibition, an inhibitor resembles the substrate in structure and competes for the active
site. Example: Malonate inhibits the enzyme Succinate Dehydrogenase as it resembles the
substrate Succinate.
[Q6] Amino Acid Zwitterion property?At specific pH, AAS have both + and - charges.
[Q7] Why is DNA called a polymer of nucleotides?Repeating nucleotide units linked by 3'-5' phosphodiester bonds.
[Q8] Difference between Nucleoside and Nucleotide.Nucleotide = Nucleoside + Phosphate group.
[Q9] Role of RuBisCO in Biosphere.Most abundant protein; fixes atmospheric CO2 during photosynthesis.
[Q10] Primary vs Secondary metabolites.Primary have direct roles in growth; secondary have roles like defense/ecological (alkaloids).
[Q11] Lock and key hypothesis of enzymes.Substrate fits perfectly into the enzyme's active site.
[Q12] Effect of pH on enzyme activity.Every enzyme has an optimum pH (e.g., Pepsin at 2, Trypsin at 8).
[Q13] Functional syncytium vs simple tissue.Coordinated function via gap junctions.
[Q14] Essential amino acids definition.Cannot be synthesized by body; must come from diet.
[Q15] Alpha-helix vs Beta-pleated sheet.Secondary structures stabilized by H-bonds.
[Q16] Km value significance.Substrate concentration at which reaction velocity is half Vmax.
[Q17] Dehydration synthesis in peptide bond.Removal of H2O to join -COOH and -NH2.
[Q18] Why is chitin found in exoskeletons?Provides structural rigidity and protection (complex polysaccharide).
[Q19] Holoenzyme components?Apoenzyme (protein) + Cofactor (non-protein).
[Q20] Most abundant protein in Animals? Biomolecules - 50 Premium FactsBiomolecules: 50 Mastery Facts
Rapid Revision Module
01
Biomolecules: Organic compounds found in living
organisms.
02
Water content: Accounts for 70-90% of the total
cellular mass.
03
Proteins: The second most abundant component (10-15%)
of cell mass.
04
Micromolecules: Molecular weight between 18 to 800
Daltons.
05
Macromolecules: Molecular weight exceeding 10,000
Daltons.
06
Amino Acids: Substituted methanes containing NH2 and
COOH groups.
07
Zwitterion: Dipolar form of amino acids occurring at
specific pH.
08
Glycine: The simplest amino acid with 'H' as the
R-group.
09
Essential AAS: 10 amino acids that must be obtained
from diet.
10
Peptide Bond: Formed by dehydration between -COOH and
-NH2.
11
Heteropolymers: Proteins are always made of different
types of amino acids.
12
Collagen: The most abundant protein in the animal
kingdom.
13
RuBisCO: The most abundant protein in the whole
biosphere.
14
Primary structure: Linear sequence, provides
positional information.
15
T-structure: Necessary for the biological activities
of proteins.
16
Lipids: Water-insoluble compounds like fatty acids and
glycerol.
17
Saturated fatty acids: Lack double bonds in their
carbon chain.
18
Lecithin: An important phospholipid found in cell
membranes.
19
Carbohydrates: Classified into mono-, di-, and
polysaccharides.
20
Inulin: A polymer of fructose used as a diagnostic
tool.
21
Chitin: N-acetyl glucosamine polymer in arthropod
exoskeletons.
22
Starch: Forms helical secondary structure to hold
Iodine (blue color).
23
Cellulose: No helices, cannot hold Iodine.
24
Glycogen: Stored form of glucose in animal livers and
muscles.
25
Nucleosides: Nitrogenous base + Sugar (e.g.,
Adenosine).
26
Nucleotides: Nucleoside + Phosphate (e.g., Adenylic
acid).
27
DNA: Double helical structure proposed by Watson and
Crick.
28
Hydrogen bonds: 2 between A-T and 3 between G-C.
29
Enzymes: Mostly proteins that catalyze biochemical
reactions.
30
Active site: Pocket where the substrate binds for
catalysis.
31
Ribozyme: An RNA molecule that acts as an enzyme.
32
Activation Energy: Energy required to initiate a
chemical reaction.
33
Exothermic reaction: Product energy is lower than
substrate energy.
34
Enzyme-Substrate Complex: Transient state during
catalysis.
35
Inhibitors: Chemicals that shut off enzyme activity.
36
Oxidoreductases: Catalyze C-O or C-N redox reactions.
37
Transferases: Transfer functional groups like methyl
or phosphate.
38
Hydrolases: Catalyze hydrolysis of ester, peptide or
glycosidic bonds.
39
Isomerases: Catalyze optical or positional
isomerizations.
40
Ligases: Catalyze linking of two compounds (e.g., C-O,
C-S bonds).
41
Prosthetic groups: Organic cofactors tightly bound
(e.g., Heme).
42
Co-enzymes: Transiently bound organic cofactors (e.g.,
vitamins).
43
Metal ions: Form coordination bonds with both
substrate and enzyme.
44
Primary metabolites: Essential for life-sustaining
processes (e.g., glucose).
45
Secondary metabolites: Alkaloids, essential oils,
drugs (e.g., Curcumin).
46
L-form: All protein amino acids are in the Left-handed
form.
47
Glycosidic bond: Joins monosaccharide units in a
carbohydrate.
48
Phosphodiester bond: Links 3' carbon of one sugar to
5' carbon of next.
49
Metabolic pool: Collection of all molecules undergoing
metabolism.
50
Km Value: Concentration of substrate at 1/2 Vmax.
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