Natural Polymers
25min Part 5 / Ch9 / Lesson 1
Prerequisites: 4-7-2
Objectives
- Understand the structure of amino acids and proteins
- Classify and describe properties of carbohydrates
- Know basic structure of nucleic acids (DNA, RNA)
Amino Acids and Proteins
Amino acids: compounds with both an amino group (-NH₂) and a carboxyl group (-COOH).
- Exist as zwitterions in solution:
- Linked by peptide bonds (-CO-NH-) to form proteins
Protein structure levels:
- Primary: amino acid sequence
- Secondary: α-helix, β-sheet
- Tertiary: 3D folding of a polypeptide chain
- Quaternary: assembly of multiple polypeptide chains
Carbohydrates
| Type | Composition | Examples | Reducing? |
|---|---|---|---|
| Monosaccharides | Cannot be hydrolyzed | Glucose C₆H₁₂O₆, Fructose | Yes |
| Disaccharides | 2 monosaccharides | Sucrose, Maltose, Lactose | Maltose: yes, Sucrose: no |
| Polysaccharides | Many monosaccharides | Starch, Cellulose, Glycogen | No |
Classification of carbohydrates
Glucose :
- Contains an aldehyde group → reducing sugar (detected by Fehling’s test, silver mirror test)
- Alcoholic fermentation:
Nucleic Acids
- DNA (deoxyribonucleic acid): double helix, stores genetic information
- RNA (ribonucleic acid): single strand, involved in protein synthesis
- Nucleotide = sugar + phosphate + base
Check Your Understanding
Q1 What type of bond links amino acids together?
Q2 Does sucrose have reducing properties?
Q3 What reagent detects starch?
Exercises
Q1. Explain why glucose is a reducing sugar in terms of its functional groups. Name two tests that confirm its reducing property.
Solution
Glucose contains an aldehyde group (-CHO), which is easily oxidized (→ carboxyl group), reducing the other reagent in the process.
Detection tests:
- Fehling’s test: heat with Fehling’s solution → red precipitate of Cu₂O forms
- Silver mirror test (Tollens’ test): warm with ammoniacal silver nitrate → metallic silver deposits on the surface