Plasma Membrane And Protein

Advanced Membrane Dynamics

Simplified Notes for CSIR-NET, GATE & DBT-BET

"Welcome to the VIP section of the cell! Here we discuss how extremophiles survive boiling acid, how lipids dance, and what happens when you blast a membrane with a laser. These are high-yield concepts."

1. Archaeal Lipids, Micelles & Liposomes

🔹 Archaeal Lipids (The Extremophiles' Armor)

Archaea survive extreme heat and pH because their membranes are chemically unique.

• Backbone: Glycerol-1-phosphate (Unlike bacteria/eukaryotes which use Glycerol-3-phosphate).
• Linkage: Ether bonds (–O–). These are highly resistant to chemical breakdown compared to ester bonds.
• Side chains: Isoprenoid chains (branched), which pack incredibly well.

📌 EXAM TIP: Ether linkage + Isoprenoid chain = The absolute hallmark of Archaea.

🔹 Micelles vs. Liposomes

Feature	Micelle	Liposome
Structure	Single layer	Bilayer
Core	Hydrophobic (No water inside)	Aqueous (Water inside)
Main Use	Lipid digestion (Bile salts)	Drug/Gene delivery

Live Animation: Micelle vs Liposome

Notice the core environments (Oil vs Water).

2. Cholesterol, Lipid Rafts & Caveolae

🔹 Lipid Rafts

These are tightly packed, detergent-resistant microdomains in the membrane. They are highly enriched in Cholesterol and Sphingolipids. They function as stable platforms for cell signaling proteins.

🔹 Caveolae ("Little Caves")

These are flask-shaped invaginations of the plasma membrane. They are essentially specialized lipid rafts that contain the protein Caveolin. They are vital for endocytosis and mechanosensing.

📌 EXAM TIP: Lipid Raft + Caveolin Protein = Caveolae.

3. Hydropathy Plot (Transmembrane Prediction)

This plot predicts if a protein crosses the membrane based on the amino acid sequence. Positive peaks on the graph mean the amino acids are water-hating (hydrophobic).

Hydropathy Index = (Σ Hydrophobicity Values) ÷ Window Size

📌 EXAM TIP: A continuous stretch of ~20 to 25 hydrophobic amino acids indicates a transmembrane alpha-helix.

4. Proving Fluidity: FRAP Technique

FRAP (Fluorescence Recovery After Photobleaching) proves lateral mobility of proteins.

• Proteins are dyed fluorescent green.
• A laser destroys the dye in one small circle (Bleaching).
• Over time, the circle turns green again because unbleached proteins randomly diffuse into the dead zone (Recovery).

Diffusion Coefficient (D) = w² / 4t
(w = radius of bleached spot, t = time for recovery)

Live Animation: The FRAP Laser

Watch lateral diffusion recover the bleached area over time.

🧠 Super Quick Revision Summary

Topic	The Absolute Key Concept
Archaeal Lipids	Ether linkages + Isoprenoid chains = Stability
Liposome vs Micelle	Liposome = Bilayer (Water core). Micelle = Monolayer (Fat core).
Lipid Raft & Caveolae	Rafts are rich in Cholesterol. Add Caveolin = Caveolae.
Hydropathy Plot	Positive peaks indicate Transmembrane alpha-helices.
FRAP	Used to prove and measure membrane fluidity / diffusion.