2.4.3 · HinglishCell Membrane & Transport
Identify membrane proteins (integral, peripheral)
2.4.3· Biology › Cell Membrane & Transport
WHAT classify kar rahe hain hum?
HOW pehchaante hain inhe? (3 lenses)
Lens 1 — Hydrophobicity (chemistry WHY)
Bilayer core oily (hydrophobic) hota hai. Koi protein region wahan sirf tab buried reh sakta hai jab uski surface bhi hydrophobic ho (nonpolar amino acids jaise Leu, Ile, Val, Phe se bani ho).
- Integral proteins mein hydrophobic stretches hote hain (aksar ek α-helix of ~20 nonpolar residues ka) jo core se match karta hai.
- Peripheral proteins overall hydrophilic hoti hain → oil se repel ho jaati hain → surface pe reh jaati hain.
Lens 2 — Kaise extract karte hain (lab test HOW)
| Treatment | Peripheral ko nikalti hai? | Integral ko nikalti hai? | Kyun |
|---|---|---|---|
| High salt / pH change | ✅ Haan | ❌ Nahi | sirf weak ionic/H-bonds todte hain |
| Urea (denaturant) | ✅ Haan | ❌ Nahi | surface attachments unfold ho jaate hain |
| Detergent (e.g. SDS, Triton) | ✅ Haan | ✅ Haan | lipid core khud dissolve ho jaata hai |
Lens 3 — Location & spanning
- Transmembrane (integral) → dono faces; channels/transporters/receptors bana sakti hain.
- Peripheral → sirf ek face; aksar enzymes, signal relays, cytoskeleton anchors hoti hain.
WHY hydrophobicity spanning predict karta hai (mini "derivation")
Worked examples
Common mistakes (Steel-man + fix)
Recall Feynman: 12-saal ke bachche ko samjhao
Socho membrane ek chocolate bar hai jo paani mein float kar rahi hai — oily middle chocolate hai. Integral proteins waise hain jaise nuts chocolate ke andar dhanse hue hain; unhe nikaalne ke liye chocolate ko pighalana padega (wahi detergent hai). Kuch nuts poori taraf se aar-paar nikle hue hain (woh transmembrane hain). Peripheral proteins waise hain jaise sprinkles sirf upar baikhe hain — unhe dhire se hilaane ya rinse karne (salt water) se ud jaate hain, kyunki woh chocolate ke andar kabhi the hi nahi. Toh poora trick yahi hai: kya yeh oily part mein dhansa hai, ya sirf surface pe baitha hai?
Flashcards
Integral proteins bilayer ke relative kahan baithe hote hain?
Hydrophobic core ke andar embedded hote hain, fatty-acid tails ke saath interact karte hain.
Integral protein ko remove karne ka SIRF effective tarika kya hai?
Detergents (ya organic solvents) jo lipid bilayer ko khud disrupt kar dein.
Peripheral protein kya nikaalti hai?
Mild treatments — high salt ya pH change — jo weak ionic/H-bonds todti hain (koi detergent nahi chahiye).
Transmembrane protein kya hota hai?
Ek integral protein jo poori bilayer ko span karta hai, dono faces pe exposed hota hai.
Kya saare integral proteins transmembrane hote hain?
Nahi — integral ke liye sirf hydrophobic core mein dip karna zaroori hai; kuch partially embedded hote hain (monotopic).
Integral proteins core mein kyon reh sakti hain?
Unke paas hydrophobic (nonpolar) amino-acid surfaces hote hain jo oily fatty-acid tails se match karte hain.
Peripheral proteins core se bahar kyon rehti hain?
Yeh hydrophilic hoti hain, isliye oily core inhe repel karta hai; yeh sirf polar surface/heads ya doosri proteins se bind karti hain.
Ek α-helix ko ~30 Å core span karne ke liye kitne residues chahiye?
Lagbhag 20 residues (30 Å ÷ 1.5 Å/residue).
Hydropathy plot pe transmembrane segment kya mark karta hai?
Ek ~20-residue-wide peak of high hydrophobicity (positive hydropathy).
Kaun sa test integral aur peripheral ko DISTINGUISH karta hai, aur kyun?
Ek mild salt/pH wash — yeh sirf peripheral ko release karta hai; integral ruka rehta hai. (Detergent dono ko release karta hai, isliye distinguish nahi kar sakta.)
Detergents integral proteins ko paani mein expose kiye bina free kyun kar lete hain?
Amphipathic detergents protein ke hydrophobic patches ke around micelles banate hain, bilayer ki jagah le lete hain.
Transmembrane proteins ke typical roles kya hain?
Channels, transporters, receptors (kuch bhi jo dono sides tak access maangta ho).
Connections
- Fluid Mosaic Model — proteins hi us fluid lipid sea mein "mosaic" tiles hain.
- Phospholipid Bilayer — iska hydrophobic core hi integral vs peripheral define karta hai.
- Membrane Transport Proteins — channels & carriers integral/transmembrane hote hain.
- Hydrophobic Effect — thermodynamic reason kyun nonpolar surfaces core mein chhup jaate hain.
- Amino Acid Properties — nonpolar residues (Leu, Ile, Val, Phe) membrane helices banate hain.
- Cell Signaling & Receptors — cytoplasmic face pe peripheral relay proteins.