Quick Summary
Biomolecules connects organic chemistry with life processes. The chapter usually tests classification, examples, reducing behaviour, peptide linkage, denaturation, vitamins, and the roles of DNA and RNA.
Carbohydrates
| Type | Meaning | Examples |
|---|---|---|
| Monosaccharides | single sugar unit | glucose, fructose |
| Disaccharides | two monosaccharides | sucrose, maltose, lactose |
| Polysaccharides | many sugar units | starch, cellulose, glycogen |
- Glucose is an aldohexose and reducing sugar.
- Fructose is a ketohexose but also gives reducing tests in alkaline medium.
- Sucrose is non-reducing; maltose and lactose are reducing.
Amino Acids and Proteins
- Amino acids contain both
-NH2and-COOH. - In solution, amino acids can exist as zwitter ions.
- Proteins are polymers of amino acids linked by peptide bonds.
- Denaturation changes secondary and tertiary structure without breaking peptide bonds.
Protein Structure (four levels)
Denaturation disrupts the secondary/tertiary structure (heat, acid) — peptide bonds (primary) stay intact, e.g. egg white cooking.
DNA vs RNA (key differences)
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Strands | Double helix | Mostly single |
| Role | Stores genetic info | Protein synthesis |
Base pairing in DNA: A=T (2 H-bonds), G≡C (3 H-bonds).
Vitamins (deficiency)
Enzymes, Vitamins, and Nucleic Acids
- Enzymes are biological catalysts with high specificity (lock-and-key model).
- Vitamins are required in small quantities; lack of vitamins causes deficiency diseases.
- DNA stores genetic information; RNA participates in protein synthesis.
Important Questions
One Mark
1. Name one reducing disaccharide. 2. What is a peptide bond? 3. Which biomolecule contains thymine? 4. Define denaturation of proteins. 5. Name one fat-soluble vitamin.
Short Answer
1. Distinguish glucose and sucrose. 2. Explain zwitter ion formation in amino acids. 3. Compare DNA and RNA. 4. Write short notes on enzyme specificity.
Long Answer
1. Classify carbohydrates with examples. 2. Explain primary, secondary, and tertiary structure of proteins. 3. Write notes on vitamins and deficiency diseases.
Common Mistakes
- Calling all disaccharides reducing sugars
- Saying denaturation breaks primary peptide bonds
- Mixing DNA bases with RNA bases
- Forgetting zwitter-ion character of amino acids
Revision Checklist
- [ ] Sugar classification and examples
- [ ] Reducing vs non-reducing sugars
- [ ] Amino acids, peptide bond, and proteins
- [ ] DNA vs RNA
- [ ] Vitamins and deficiency examples