Electron Configuration:

1s² 2s² 2p²

Why Four Bonds?

• Carbon needs 8 electrons in its outer shell to be stable (octet rule)
• It has 4 valence electrons, so needs 4 more electrons
• By sharing its 4 electrons with 4 other atoms, carbon achieves stability
• Each shared pair of electrons = one covalent bond
• Result: Carbon can form 4 covalent bonds

Step-by-Step Process:

1. Monomer A has a hydroxyl group (-OH)
2. Monomer B has a hydrogen atom (-H)
3. The -OH from one monomer and the -H from the other combine to form H₂O (water)
4. The two monomers are now bonded together where the -OH and -H were removed
5. A new covalent bond is formed (specific type depends on the molecules)

General Equation:

Monomer A + Monomer B → Polymer + H₂O

Step-by-Step Process:

1. Water molecule (H₂O) is added to the polymer
2. The covalent bond between two monomers is broken
3. The water splits into H⁺ and OH⁻
4. One monomer gains the -OH group
5. The other monomer gains the -H atom
6. Two separate monomers are now produced

General Equation:

Polymer + H₂O → Monomer A + Monomer B

Key Properties:

• Soluble in water (polar molecules with many -OH groups)
• Sweet taste
• White crystalline solids at room temperature
• General formula: (CH₂O)_n where n = 3 to 7
• Reducing sugars (can donate electrons in redox reactions)

Molecular Formula: C₆H₁₂O₆

Glucose is a hexose sugar (6 carbons) and the primary energy source for most organisms. It exists in both linear and ring forms, with the ring form predominating in solution.

🔑 Key Point:

The difference between α and β glucose is just the position of the -OH group on carbon 1, but this small difference has huge consequences for the properties of polymers they form!

Key Properties:

• Insoluble or poorly soluble in water (due to large size)
• Not sweet
• Compact storage molecules (don't affect osmotic pressure)
• Can be branched or unbranched
• Serve as energy storage or structural support

Composition: Polymer of α-glucose

Starch is the primary energy storage molecule in plants. It is stored in chloroplasts (as small granules) and in storage organs like roots, tubers, and seeds.

Two Components:

1. Amylose (10-30%): Unbranched chain of α-glucose in α-1,4 glycosidic bonds. Forms a helix structure. Compact.
2. Amylopectin (70-90%): Branched chain with α-1,4 bonds in chains and α-1,6 bonds at branch points (every 25-30 glucose units). Highly branched = rapid glucose release.

Functions:

• Energy storage in plants
• Compact and insoluble (doesn't affect water potential)
• Easily broken down to glucose when energy is needed
• Major component of human diet (potatoes, rice, wheat, corn)

Composition: Polymer of α-glucose

Glycogen is the primary energy storage molecule in animals and fungi. It is stored mainly in the liver and muscles.

Structure:

• Similar to amylopectin but MORE highly branched
• Branches occur every 8-12 glucose units
• α-1,4 glycosidic bonds in chains; α-1,6 bonds at branch points
• More compact than starch

Functions:

• Short-term energy storage in animals
• Stored in liver (maintains blood glucose) and muscles (for muscle contraction)
• Highly branched = VERY RAPID glucose release when energy is needed
• Compact and insoluble

🔍 Why highly branched? More branch points = more ends where enzymes can simultaneously break off glucose = faster mobilization of energy!

Key Structural Features:

1. Monomer: β-glucose units (NOT α-glucose)
2. Bonds: β-1,4 glycosidic bonds between glucose units
3. Chain length: 500-14,000 glucose molecules per cellulose chain
4. Configuration: Alternate β-glucose molecules are rotated 180° relative to neighbors
5. Shape: Long, straight, unbranched chains

🔑 Critical Difference from Starch/Glycogen:

Because cellulose is made of β-glucose (not α-glucose), every other glucose molecule is flipped upside-down. This allows the chains to pack tightly together in straight, parallel arrangements.

Formation of Microfibrils:

• Multiple cellulose chains (40-70) run parallel to each other
• Hydrogen bonds form between -OH groups on adjacent chains
• These bonds hold the chains together tightly
• Creates cellulose microfibrils—bundles of cellulose chains
• Microfibrils are crystalline (highly ordered) and very strong

💪 Strength: Cellulose microfibrils have tensile strength comparable to steel! The extensive hydrogen bonding between chains makes cellulose extremely strong and rigid.

1. Cell-Cell Recognition

Glycoproteins on cell surfaces act as identification tags. They allow cells to recognize each other as "self" vs. "foreign." Important for immune responses and tissue formation.

2. Cell Adhesion

Help cells stick together to form tissues. Glycoproteins bind to other glycoproteins or proteins on adjacent cells, holding tissues together.

3. Cell Signaling (Receptors)

Many membrane receptor proteins are glycoproteins. The carbohydrate portion helps receptors bind to signaling molecules (hormones, growth factors).

4. Immune Response

Antibodies (immunoglobulins) are glycoproteins. Blood group antigens (A, B, O) are determined by glycoproteins on red blood cells.

5. Structural Stability

The carbohydrate portion makes proteins more stable and soluble. It protects proteins from degradation.

6. Lubrication and Protection

Mucins are glycoproteins in mucus that lubricate and protect epithelial surfaces (respiratory tract, digestive system).

Components:

• 1 glycerol molecule: A 3-carbon alcohol with 3 hydroxyl (-OH) groups
• 3 fatty acid molecules: Long hydrocarbon chains with a carboxyl group (-COOH) at one end

Formation:

1. Each fatty acid undergoes a condensation reaction with one of the -OH groups on glycerol
2. An ester bond forms between glycerol and each fatty acid
3. 3 water molecules are released (one per ester bond)
4. Result: A triglyceride molecule with 3 ester bonds

Components:

• 1 glycerol molecule
• 2 fatty acid chains (not 3 like triglycerides)
• 1 phosphate group (attached to the 3rd position of glycerol)
• Often an additional small molecule attached to the phosphate (e.g., choline, serine)

Formation:

• 2 ester bonds form between glycerol and 2 fatty acids (condensation)
• 1 bond forms between glycerol and phosphate group
• Phosphate may be further linked to another molecule (e.g., choline in phosphatidylcholine)

Function: Formation of the Phospholipid Bilayer

When placed in water, phospholipids spontaneously arrange themselves into a bilayer. The hydrophilic heads face the outer and inner aqueous environments, while the hydrophobic tails are shielded in the middle. This bilayer is the fundamental structure of all cell membranes.