Biomolecules - NCERT Solutions

Chapter Overview

Biomolecules are the organic molecules that are essential for life. This chapter covers various types of biomolecules including carbohydrates, proteins, nucleic acids, lipids, and enzymes that play crucial roles in living organisms.

Key Concepts:

• Primary Metabolites: Essential for normal growth and development
• Secondary Metabolites: Not essential for growth but have ecological functions
• Macromolecules: Large molecular weight biomolecules
• Biomacromolecules: Proteins, nucleic acids, polysaccharides
• Enzymes: Biocatalysts that speed up biochemical reactions

NCERT Exercise Solutions

Exercise 9.1

Question: What are macromolecules? Give examples.

Solution: Macromolecules are large, complex molecules with high molecular weights, typically formed by the polymerization of smaller subunits called monomers.

Examples:

1. Proteins: Polymers of amino acids (e.g., hemoglobin, enzymes)
2. Nucleic Acids: Polymers of nucleotides (DNA, RNA)
3. Polysaccharides: Polymers of monosaccharides (starch, cellulose, glycogen)
4. Lipids: Though not true polymers, they are large biological molecules

Characteristics of Macromolecules:

• High molecular weight (typically > 10,000 Daltons)
• Formed by polymerization of monomers
• Have specific three-dimensional structures
• Perform specific biological functions

Exercise 9.2

Question: Illustrate a glycosidic, peptide and a phosphodiester bond.

Solution:

1. Glycosidic Bond:

• Formed between two monosaccharide units
• Type: Condensation reaction (removal of water)
• Example: Maltose formation from two glucose molecules

Glucose + Glucose → Maltose + H₂O
   (C1-OH) + (C4-OH) → (C1-O-C4) + H₂O

2. Peptide Bond:

• Formed between amino group of one amino acid and carboxyl group of another
• Type: Condensation reaction
• Example: Dipeptide formation

Amino acid 1 + Amino acid 2 → Dipeptide + H₂O
   (NH₂) + (COOH) → (NH-CO) + H₂O

3. Phosphodiester Bond:

• Formed between 3’-OH of one nucleotide and 5’-phosphate of another
• Type: Condensation reaction
• Found in: DNA and RNA backbone

Nucleotide 1 + Nucleotide 2 → Dinucleotide + H₂O
   (3'-OH) + (5'-PO₄) → (3'-O-PO₄-5') + H₂O

Exercise 9.3

Question: What is meant by the tertiary structure of proteins?

Solution: Tertiary structure of proteins refers to the three-dimensional arrangement of all amino acid residues in a single polypeptide chain. It represents the complete folding of the polypeptide chain into a specific 3D shape.

Features:

1. Overall 3D Shape: Complete spatial arrangement of the protein

2. Stabilizing Forces:

   • Hydrogen bonds
   • Disulfide bonds (-S-S-)
   • Ionic bonds (salt bridges)
   • Hydrophobic interactions
   • Van der Waals forces

3. Types of Folds:

   • α-helix and β-sheet arrangement
   • Random coils
   • Turn and loops

4. Functional Significance:

   • Determines biological activity
   • Forms active sites of enzymes
   • Determines protein specificity

Example: Myoglobin has a tertiary structure that creates a pocket for heme group binding.

Exercise 9.4

Question: Find and write down structures of 10 interesting small molecular weight biomolecules. Find if there is any industry which manufactures the compounds by isolation. Find out who are the buyers.

Solution:

1. Curcumin

• Structure: C₂₁H₂₀O₆, diarylheptanoid compound
• Source: Turmeric (Curcuma longa)
• Industry: Pharmaceutical and food industry
• Buyers: Pharmaceutical companies, nutraceutical manufacturers, food processors

2. Caffeine

• Structure: C₈H₁₀N₄O₂, xanthine alkaloid
• Source: Coffee beans, tea leaves, cocoa
• Industry: Beverage and pharmaceutical industry
• Buyers: Beverage companies, pharmaceutical manufacturers, supplement producers

3. Quinine

• Structure: C₂₀H₂₄N₂O₂, quinoline alkaloid
• Source: Cinchona bark
• Industry: Pharmaceutical industry
• Buyers: Pharmaceutical companies, antimalarial drug manufacturers

4. Nicotine

• Structure: C₁₀H₁₄N₂, pyridine alkaloid
• Source: Tobacco leaves
• Industry: Pharmaceutical industry (cessation products)
• Buyers: Pharmaceutical companies, research institutions

5. Morphine

• Structure: C₁₇H₁₉NO₃, phenanthrene alkaloid
• Source: Opium poppy (Papaver somniferum)
• Industry: Pharmaceutical industry
• Buyers: Pharmaceutical companies, pain management drug manufacturers

6. Salicylic Acid

• Structure: C₇H₆O₃, phenolic acid
• Source: Willow bark, meadowsweet
• Industry: Pharmaceutical and cosmetic industry
• Buyers: Pharmaceutical companies, cosmetic manufacturers, chemical industry

7. Reserpine

• Structure: C₃₃H₄₀N₂O₉, indole alkaloid
• Source: Rauwolfia serpentina
• Industry: Pharmaceutical industry
• Buyers: Pharmaceutical companies, antihypertensive drug manufacturers

8. Strychnine

• Structure: C₂₁H₂₂N₂O₂, indole alkaloid
• Source: Strychnos nux-vomica
• Industry: Research chemical industry
• Buyers: Research institutions, neuroscience laboratories

9. Atropine

• Structure: C₁₇H₂₃NO₃, tropane alkaloid
• Source: Atropa belladonna (deadly nightshade)
• Industry: Pharmaceutical industry
• Buyers: Pharmaceutical companies, ophthalmic drug manufacturers

10. Digoxin

• Structure: C₄₁H₆₄O₁₄, cardiac glycoside
• Source: Digitalis purpurea (foxglove)
• Industry: Pharmaceutical industry
• Buyers: Pharmaceutical companies, cardiovascular drug manufacturers

NCERT Highlights for NEET

🎯 Important Concepts for NEET:

1. Amino Acid Structure: Central carbon with NH₂, COOH, H, and R group
2. Protein Structure Levels: Primary, secondary, tertiary, quaternary
3. Enzyme Classification: Based on type of reaction catalyzed
4. Nucleic Acid Structure: Sugar-phosphate backbone with nitrogenous bases

🧬 Key Points for NEET:

1. Essential Amino Acids: 8 amino acids that cannot be synthesized by humans
2. Types of RNA: mRNA, tRNA, rRNA with specific functions
3. DNA Structure: Double helix with complementary base pairing
4. ATP: Energy currency of the cell

NEET Practice Questions

Question 1 (NEET Level)

Statement: Which of the following is a reducing sugar? (A) Sucrose (B) Starch (C) Cellulose (D) Maltose

Solution: Reducing sugars are those that have free aldehyde or ketone groups or can open to form them.

Analyzing each option:

• Sucrose: Non-reducing (glycosidic bond involves both anomeric carbons)
• Starch: Polymer of glucose, mainly non-reducing (amylose and amylopectin)
• Cellulose: Polymer of glucose, non-reducing
• Maltose: Disaccharide of glucose, reducing (one anomeric carbon free)

Answer: Option (D) Maltose

Question 2 (NEET Level)

Statement: The enzyme that converts glucose to glucose-6-phosphate is: (A) Hexokinase (B) Phosphoglucomutase (C) Phosphoglucoisomerase (D) Glucose-6-phosphatase

Solution: Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate, the first step of glycolysis.

Reaction: Glucose + ATP → Glucose-6-phosphate + ADP

Answer: Option (A) Hexokinase

Important Biomolecules and Their Functions

1. Carbohydrates

Monosaccharides:

• Glucose: Primary energy source
• Fructose: Fruit sugar, energy source
• Galactose: Component of lactose

Disaccharides:

• Sucrose: Table sugar (glucose + fructose)
• Lactose: Milk sugar (glucose + galactose)
• Maltose: Malt sugar (glucose + glucose)

Polysaccharides:

• Starch: Energy storage in plants
• Glycogen: Energy storage in animals
• Cellulose: Structural component in plants
• Chitin: Structural component in fungi and arthropods

2. Proteins

Amino Acids (20 types):

• Essential: Cannot be synthesized by body (8 amino acids)
• Non-essential: Can be synthesized by body (12 amino acids)

Protein Types:

• Structural: Collagen, keratin
• Enzymatic: Amylase, lipase, protease
• Transport: Hemoglobin, albumin
• Regulatory: Hormones like insulin

3. Nucleic Acids

DNA Structure:

• Double helix with complementary base pairing
• Bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T)
• Sugar-phosphate backbone with deoxyribose sugar

RNA Types:

• mRNA: Messenger RNA, carries genetic information
• tRNA: Transfer RNA, brings amino acids during translation
• rRNA: Ribosomal RNA, structural component of ribosomes

Enzymes and Their Properties

Enzyme Characteristics:

1. Protein Nature: Most enzymes are proteins
2. Specificity: Each enzyme acts on specific substrate
3. Catalytic Efficiency: Speed up reactions by 10⁶-10¹² times
4. Optimal Conditions: Work best at specific pH and temperature
5. Regulation: Activity can be regulated

Enzyme Classification:

1. Oxidoreductases: Oxidation-reduction reactions
2. Transferases: Transfer of functional groups
3. Hydrolases: Hydrolysis reactions
4. Lyases: Addition to double bonds or removal of groups
5. Isomerases: Rearrangement of atoms
6. Ligases: Joining of molecules with ATP

Success Tips

1. Memorize Structures: Focus on biomolecule structures and functional groups
2. Understand Functions: Connect structure to biological function
3. Practice Reactions: Master enzyme-catalyzed reactions
4. Create Flow Charts: Visualize metabolic pathways

Master Biomolecules

Biomolecules are the building blocks of life. Focus on structure-function relationships for NEET success!

Remember: Every detail in NCERT Biomolecules is important for NEET. Read each line carefully and understand the concepts thoroughly!

For additional practice, check out our Biology Practice Problems section.