Class 11 Biology - Biomolecules

Notes

Key Concepts

Analysis of Chemical Composition

Organic Compounds: Living tissue (vegetable or liver) is ground in trichloroacetic acid (Cl₃CCOOH). Filtering through cheesecloth yields two fractions:
- Acid-soluble pool (Filtrate): Contains thousands of small organic compounds (micromolecules).
- Acid-insoluble fraction (Retentate): Contains macromolecules like proteins, polysaccharides, and nucleic acids.
Inorganic Elements: Obtained by burning tissue to "ash." Elements like Calcium, Magnesium, Sodium, and compounds like sulphate and phosphate are identified.
Biomolecules: All carbon compounds obtained from living tissues.

Amino Acids

Structure: Organic compounds containing an amino group (-NH₂) and an acidic carboxyl group (-COOH) on the same α-carbon. They are substituted methanes.
R Group: The variable group determines the amino acid.
- Glycine (R = H)
- Alanine (R = -CH₃)
- Serine (R = -CH₂OH)
Types: 20 types occur in proteins. Can be acidic (Glutamic acid), basic (Lysine), neutral (Valine), or aromatic (Tyrosine, Phenylalanine, Tryptophan).
Zwitterion: In different pH solutions, the structure changes due to the ionizable nature of amino and carboxyl groups.

Lipids

Generally water-insoluble.
Fatty Acids: Carboxyl group attached to an R group (1-19 carbons). Palmitic acid (16C), Arachidonic acid (20C). Can be saturated (no double bonds) or unsaturated.
Glycerol: Trihydroxy propane.
Triglycerides: Glycerol esterified with three fatty acids.
Phospholipids: Lipids with a phosphorus and a phosphorylated organic compound (e.g., Lecithin in cell membranes).

Nitrogen Bases, Nucleosides, and Nucleotides

Nitrogen Bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Uracil, Thymine).
Nucleosides: Nitrogen base + Sugar (e.g., Adenosine, Guanosine, Uridine, Cytidine).
Nucleotides: Nucleoside + Phosphate group (e.g., Adenylic acid, Guanylic acid). These are the building blocks of nucleic acids (DNA and RNA).

Primary and Secondary Metabolites

Primary Metabolites: Have identifiable functions and roles in normal physiological processes (e.g., amino acids, sugars).
Secondary Metabolites: Produced in plants, fungi, and microbes; functions are not always clear but useful to human welfare (e.g., alkaloids, rubber, antibiotics, spices, pigments).

Biomacromolecules

Found in the acid-insoluble fraction with molecular weights > 10,000 Da (except lipids).
Proteins: Heteropolymers of amino acids. Linear chains linked by peptide bonds.
- Collagen: Most abundant protein in the animal world.
- RuBisCO: Most abundant protein in the whole biosphere.
Polysaccharides: Long chains of sugars.
- Cellulose: Homopolymer of glucose; found in plant cell walls.
- Starch: Energy store in plants; forms helical secondary structures.
- Glycogen: Energy store in animals.
- Chitin: Complex polysaccharide in arthropod exoskeletons.
Nucleic Acids: Polynucleotides (DNA/RNA).

Structure of Proteins

Primary Structure: The sequence/positional information of amino acids.
Secondary Structure: Folding of the thread into forms like the α-helix (right-handed) or β-pleated sheets.
Tertiary Structure: 3D folding of the protein chain upon itself; essential for biological activity.
Quaternary Structure: Assembly of multiple polypeptide subunits (e.g., Haemoglobin: 2α and 2β subunits).

Enzymes

Nature: Almost all are proteins. Some are nucleic acids (Ribozymes).
Mechanism: Have an 'active site' (crevice) where the substrate fits. They lower the Activation Energy required for a reaction.
Catalytic Cycle:
1. Substrate binds to active site.
2. Enzyme alters shape (induced fit).
3. Bonds broken/made; ES complex forms transition state.
4. Products released; enzyme ready for next cycle.
Factors Affecting Activity:
- Temperature: Enzymes display maximum activity at an optimum temperature. Low temperatures preserve the enzyme in a temporarily inactive state, whereas high temperatures destroy enzymatic activity because heat denatures proteins by breaking hydrogen and ionic bonds.
- pH: Every enzyme operates optimally at a specific optimum pH. Alterations in pH disrupt the ionic state of amino acid residues, affecting active site charge and substrate binding.
- Substrate Concentration & Michaelis-Menten Kinetics:
- The reaction velocity increases with substrate concentration $[S]$ until it reaches a maximum velocity ( $V_{max}$ ), at which point all active sites are saturated.
- The Michaelis Constant ( $K_m$ ) represents the substrate concentration at which the reaction velocity is half of $V_{max}$ . A low $K_m$ value indicates high substrate-enzyme affinity.

Inhibitors: Chemicals that bind to an enzyme to inhibit its catalytic activity.
- Competitive Inhibitor: Resembles the substrate structurally and binds to the active site. It increases the apparent $K_m$ $K_{m}$ while leaving $V_{max}$ $V_{ma x}$ unchanged.
  - Example: Malonate competes with succinate for the active site of succinate dehydrogenase. This is commonly used to control pathogens.
- Non-Competitive Inhibitor: Binds to an allosteric site (not the active site), changing the shape of the enzyme. It decreases the $V_{max}$ while leaving the $K_m$ unchanged.
Classification:
1. Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases.
Co-factors: Non-protein constituents making the enzyme active.
- Apoenzyme: Protein portion.
- Prosthetic groups: Tightly bound (e.g., Haem).
- Co-enzymes: Transiently bound organic compounds (e.g., NAD, NADP containing Niacin).
- Metal Ions: e.g., Zinc for carboxypeptidase. peptidase.

Key Concepts

Organic Compounds: Living tissue (vegetable or liver) is ground in trichloroacetic acid (Cl₃CCOOH). Filtering through cheesecloth yields two fractions:

Acid-soluble pool (Filtrate): Contains thousands of small organic compounds (micromolecules).
Acid-insoluble fraction (Retentate): Contains macromolecules like proteins, polysaccharides, and nucleic acids.

Inorganic Elements: Obtained by burning tissue to "ash." Elements like Calcium, Magnesium, Sodium, and compounds like sulphate and phosphate are identified.

Biomolecules: All carbon compounds obtained from living tissues.

Structure: Organic compounds containing an amino group (-NH₂) and an acidic carboxyl group (-COOH) on the same α-carbon. They are substituted methanes.

R Group: The variable group determines the amino acid.

Glycine (R = H)
Alanine (R = -CH₃)
Serine (R = -CH₂OH)

Types: 20 types occur in proteins. Can be acidic (Glutamic acid), basic (Lysine), neutral (Valine), or aromatic (Tyrosine, Phenylalanine, Tryptophan).

Zwitterion: In different pH solutions, the structure changes due to the ionizable nature of amino and carboxyl groups.

Generally water-insoluble.

Fatty Acids: Carboxyl group attached to an R group (1-19 carbons). Palmitic acid (16C), Arachidonic acid (20C). Can be saturated (no double bonds) or unsaturated.

Glycerol: Trihydroxy propane.

Triglycerides: Glycerol esterified with three fatty acids.

Phospholipids: Lipids with a phosphorus and a phosphorylated organic compound (e.g., Lecithin in cell membranes).

Nitrogen Bases: Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Uracil, Thymine).

Nucleosides: Nitrogen base + Sugar (e.g., Adenosine, Guanosine, Uridine, Cytidine).

Nucleotides: Nucleoside + Phosphate group (e.g., Adenylic acid, Guanylic acid). These are the building blocks of nucleic acids (DNA and RNA).

Primary Metabolites: Have identifiable functions and roles in normal physiological processes (e.g., amino acids, sugars).

Secondary Metabolites: Produced in plants, fungi, and microbes; functions are not always clear but useful to human welfare (e.g., alkaloids, rubber, antibiotics, spices, pigments).

Found in the acid-insoluble fraction with molecular weights > 10,000 Da (except lipids).

Proteins: Heteropolymers of amino acids. Linear chains linked by peptide bonds.

Collagen: Most abundant protein in the animal world.
RuBisCO: Most abundant protein in the whole biosphere.

Polysaccharides: Long chains of sugars.

Cellulose: Homopolymer of glucose; found in plant cell walls.
Starch: Energy store in plants; forms helical secondary structures.
Glycogen: Energy store in animals.
Chitin: Complex polysaccharide in arthropod exoskeletons.

Nucleic Acids: Polynucleotides (DNA/RNA).

Primary Structure: The sequence/positional information of amino acids.

Secondary Structure: Folding of the thread into forms like the α-helix (right-handed) or β-pleated sheets.

Tertiary Structure: 3D folding of the protein chain upon itself; essential for biological activity.

Quaternary Structure: Assembly of multiple polypeptide subunits (e.g., Haemoglobin: 2α and 2β subunits).

Nature: Almost all are proteins. Some are nucleic acids (Ribozymes).

Mechanism: Have an 'active site' (crevice) where the substrate fits. They lower the Activation Energy required for a reaction.

Catalytic Cycle:

Substrate binds to active site.
Enzyme alters shape (induced fit).
Bonds broken/made; ES complex forms transition state.
Products released; enzyme ready for next cycle.

Factors Affecting Activity:

Temperature: Enzymes display maximum activity at an optimum temperature. Low temperatures preserve the enzyme in a temporarily inactive state, whereas high temperatures destroy enzymatic activity because heat denatures proteins by breaking hydrogen and ionic bonds.
pH: Every enzyme operates optimally at a specific optimum pH. Alterations in pH disrupt the ionic state of amino acid residues, affecting active site charge and substrate binding.
Substrate Concentration & Michaelis-Menten Kinetics:
The reaction velocity increases with substrate concentration $[S]$ until it reaches a maximum velocity ( $V_{max}$ ), at which point all active sites are saturated.
The Michaelis Constant ( $K_m$ ) represents the substrate concentration at which the reaction velocity is half of $V_{max}$ . A low $K_m$ value indicates high substrate-enzyme affinity.

Inhibitors: Chemicals that bind to an enzyme to inhibit its catalytic activity.

Competitive Inhibitor: Resembles the substrate structurally and binds to the active site. It increases the apparent $K_m$ $K_{m}$ while leaving $V_{max}$ $V_{ma x}$ unchanged.
- Example: Malonate competes with succinate for the active site of succinate dehydrogenase. This is commonly used to control pathogens.
Non-Competitive Inhibitor: Binds to an allosteric site (not the active site), changing the shape of the enzyme. It decreases the $V_{max}$ while leaving the $K_m$ unchanged.

Classification:

Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases.

Co-factors: Non-protein constituents making the enzyme active.

Apoenzyme: Protein portion.
Prosthetic groups: Tightly bound (e.g., Haem).
Co-enzymes: Transiently bound organic compounds (e.g., NAD, NADP containing Niacin).
Metal Ions: e.g., Zinc for carboxypeptidase. peptidase.

Class 11 Biology - Biomolecules

Class 11 Biology - Biomolecules

Notes

Key Concepts

Analysis of Chemical Composition

Amino Acids

Lipids

Nitrogen Bases, Nucleosides, and Nucleotides

Primary and Secondary Metabolites

Biomacromolecules

Structure of Proteins

Enzymes

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Class 11 Biology - Biomolecules

Class 11 Biology - Biomolecules

Notes

Key Concepts

Analysis of Chemical Composition

Amino Acids

Lipids

Nitrogen Bases, Nucleosides, and Nucleotides

Primary and Secondary Metabolites

Biomacromolecules

Structure of Proteins

Enzymes

On this page