🧬 Biomacromolecules
During chemical analysis of cells, some biomolecules are found in the acid-insoluble fraction (retentate). These large-sized molecules are called biomacromolecules.
⭐ Key Characteristics
- Molecular Weight: Generally 10,000 Daltons and above.
- Types: Proteins, Nucleic Acids, Polysaccharides, and Lipids.
- Solubility: Insoluble in acid
- Composition: Water is the most abundant chemical in living organisms (70-90%), followed by proteins (10-15%).
🔴 Important NCERT Exception – Lipids
Lipids have low molecular weight (< 800 Da), yet they are placed in the acid-insoluble fraction because they form membrane vesicles during grinding. Hence:
Lipids are not true macromolecules (not polymers) but behave like one during analysis.
📌 Memory Point:
Acid-insoluble = Large size OR vesicle-forming
🧠 1️⃣ Proteins – Functional Workhorses of Cells
Proteins are polymers of amino acids linked by peptide bonds. Each protein is a polypeptide chain.
🔹 Basic Features
- Made of 20 different amino acids
- Always heteropolymers (never homopolymers)
- Amino acids are arranged in a specific sequence (decided by genes)
📌 Bond Involved: Peptide bond (–CO–NH–)
🔹 Classification of Amino Acids (Diet-Based)
- Essential amino acids: Cannot be synthesized by humans → must come from diet
- Non-essential amino acids: Can be synthesized by the body
🔹 Functions of Proteins
| Function | Example |
|---|---|
| Transport | Hemoglobin, GLUT-4 |
| Defense | Antibodies |
| Hormones | Insulin |
| Enzymes | Trypsin, Amylase |
| Structural | Collagen, Keratin |
⭐ Special Facts to Memorize
- Collagen: Most abundant protein in animals
- RuBisCO: Most abundant protein in the entire biosphere
🧠 Memory Line:
Proteins do almost everything except store genetic information.
🍞 2️⃣ Polysaccharides – Carbohydrate Polymers
Polysaccharides are long chains of monosaccharides joined by glycosidic bonds. They are mainly energy storage or structural molecules.
🟩 A. Cellulose – Structural Polysaccharide
- Type: Homopolymer
- Monomer: β-glucose
- Function: Forms plant cell wall
- Structure: Straight, linear chains
- Iodine test: ❌ No blue color
📌 Key Point: Humans cannot digest cellulose.
🟦 B. Starch – Plant Storage Polysaccharide
- Function: Energy storage in plants
- Components: Amylose (helical) + Amylopectin (branched)
- Iodine test: ✅ Blue-black color
🧠 Memory Trick:
Helix + iodine = blue
🟥 C. Glycogen – Animal Storage Polysaccharide
- Function: Energy storage in animals (liver & muscles)
- Structure: Highly branched (more than starch)
- Ends:
- Reducing end (right)
- Non-reducing ends (left, many)
📌 Key Fact: Fastest glucose release due to high branching.
🟪 D. Chitin – Protective Polysaccharide
- Found in: Arthropod exoskeleton & fungal cell wall
- Type: Heteropolymer
- Monomer: N-acetyl glucosamine (NAG)
🧠 Memory Line:
Chitin = protection + rigidity
🧠 Quick Comparison (Must Remember)
| Polysaccharide | Function | Found In | Monomer |
|---|---|---|---|
| Cellulose | Structure | Plants | β-glucose |
| Starch | Storage | Plants | α-glucose |
| Glycogen | Storage | Animals | α-glucose |
| Chitin | Protection | Arthropods, fungi | NAG |
💡 Questions and Answers
Q1. What are biomacromolecules?
A1. Biomacromolecules are large organic molecules like proteins and polysaccharides that are found in the acid-insoluble fraction of cells and have very high molecular weight.
🔑 Key Points: Large size, acid-insoluble.
Q2. Why are lipids placed under biomacromolecules despite being small?
A2. Lipids form membrane vesicles when cells are broken. These vesicles are large and insoluble, so lipids remain in the acid-insoluble fraction.
🔑 Key Points: Vesicle formation, not true polymers.
Q3. What is a peptide bond?
A3. A peptide bond is a covalent bond formed between two amino acids by removal of a water molecule, linking the –COOH group of one amino acid with the –NH₂ group of another.
🔑 Key Points: Dehydration reaction, links amino acids.
Q4. Differentiate between starch and cellulose.
A4. Starch stores energy in plants and gives a blue color with iodine, while cellulose provides structural support and does not react with iodine.
🔑 Key Points: Storage vs structure.
Q5. What is quaternary structure of proteins?
A5. It refers to the association of two or more polypeptide chains to form a functional protein. Example: Hemoglobin.
🔑 Key Points: Multiple subunits, functional complex.