Explain facilitated diffusion and channel - carrier proteins

2.4.8 · Biology › Cell Membrane & Transport

Facilitated diffusion KYA hai?

Shabd "facilitated" = aasaan banana. Shabd "diffusion" = high se low concentration ki taraf spontaneous failna. Toh: diffusion jise ek protein aasaan banata hai.

Do tarah ke helper proteins

Figure — Explain facilitated diffusion and channel - carrier proteins

1. Channel proteins — "open tunnel"

KYA move karta hai: zyaadatar ions ( $K^{+}$ , $N a^{+}$ , $C a^{2 +}$ ) aur paani.
Selective KAISE hota hai: pore ki width + charged amino acids ek filter ki tarah kaam karte hain — sirf sahi size/charge wala fit hota hai.
Special types:
- Gated channels — signal ke response mein open/close hote hain (voltage, ligand, stretch).
- Aquaporins — paani-specific channels.

2. Carrier proteins — "revolving door"

KYA move karta hai: bade polar molecules jaise glucose (e.g. GLUT transporters) aur amino acids.
Selective KAISE hota hai: ek specific binding site (lock-and-key) — sirf sahi molecule fit hota hai.
Kyunki carriers ki ek fixed sankhya hoti hai, rate saturate ho jaati hai (neeche dekho).

ATP KYUN nahi? — Flow ki direction derive karna

Ek substance spontaneously move karta hai agar aisa karne se free energy kam hoti hai ( $Δ G < 0$ ). Ek uncharged solute ke liye jo side "in" se side "out" cross karta hai:

$Δ G = R T ln (\frac{C _{o u t}}{C _{in}})$

Ions ke liye, charge bhi matter karta hai, jo electrochemical version deta hai:

$Δ G = R T ln (\frac{C _{o u t}}{C _{in}}) + z F Δ V$

jahan $z$ = ion charge, $F$ = Faraday's constant, $Δ V$ = membrane voltage. Ions combined concentration + electrical gradient ko follow karte hain.

Carriers saturate KYUN karte hain — Kinetics derive karna

Binding ko enzyme kinetics ki tarah treat karo. Solute $S$ carrier $T$ ko bind kare:

$T + S ⇌ T S \to T + S_{(o t h er s i d e)}$

Yeh ek Michaelis–Menten-shaped curve deta hai:

$V = \frac{V _{ma x} [ S ]}{K _{m} + [ S ]}$

Yeh contrast — carriers saturate karte hain, channels nahi — ek classic exam discriminator hai.

Common mistakes (Steel-man + fix)

Flashcards

Facilitated diffusion ko kaun sa energy source drive karta hai?

Pre-existing electrochemical gradient — koi ATP nahi.

Facilitated diffusion define karo.

Ek substance ka passive transport jo apne electrochemical gradient ke neeche channel ya carrier protein ke through hota hai, bina ATP ke.

Glucose simple diffusion se membrane cross KYUN nahi kar sakta?

Yeh bada aur polar hai, isliye hydrophobic lipid core ise repel karta hai.

Channel protein solutes ko KAISE move karta hai?

Yeh ek continuous hydrophilic pore banata hai; solutes bina tight binding ya shape change ke flow karte hain.

Carrier protein solutes ko KAISE move karta hai?

Yeh solute ko bind karta hai, conformational change karta hai, aur doosri taraf release kar deta hai.

Channels ya carriers mein se kaun fast hai aur KYUN?

Channels — inke paas open pore hota hai bina slow shape-change cycle ke.

Carrier-mediated rates saturate KYUN hoti hain lekin channel rates nahi?

Carriers mein finite binding sites hoti hain (

V_{ma x}

); channels open pores hain bina binding step ke.

Carrier saturation equation likho.

V = \frac{V _{ma x} [ S ]}{K _{m} + [ S ]}

K_{m}

kya represent karta hai?

Woh solute concentration jo

V_{ma x}

ka half deta hai; binding affinity ka measure.

Ek ion ke membrane cross karne ke liye

Δ G

ki equation?

Δ G = R T ln (C_{o u t} / C_{in}) + z F Δ V

Aquaporin kya hai?

Ek water-selective channel protein.

Facilitated diffusion equilibrium pe KYUN rukta hai?

C_{in} = C_{o u t}

(aur ions ke liye electrical balance)

Δ G = 0

banata hai, toh net flux zero ho jaati hai.

Facilitated diffusion aur active transport mein fark?

Facilitated = passive, downhill, koi ATP nahi; active = uphill, energy chahiye (ATP ya coupled gradient).

Recall Feynman: ek 12-saal ke bachche ko samjhao

Ek bheed wale kamre (high concentration) aur ek khaali kamre (low concentration) ke beech ek diwar ka imagine karo. Log naturally khaali kamre mein failna chahte hain — lekin diwar mein koi darwaza nahi hai. Facilitated diffusion matlab diwar mein ek darwaza lagana. Log khud se guzar jaate hain; kisi ko unhe dhakkelna nahi padta, kyunki wo already failna chahte the. Channel ek khula darwaaza hai (fast). Carrier ek revolving door hai — tum andar jaate ho, woh tumhe doosri taraf spin karti hai (slower). Jab dono kamron mein utne hi log ho jaate hain, utne hi log dono taraf jaate hain, toh kuch change nahi lagta.

Connections

Simple Diffusion — wahi downhill principle, lekin koi protein nahi chahiye (chhote non-polar molecules).
Active Transport — opposite case: uphill movement jisme ATP chahiye (e.g. Na⁺/K⁺ pump).
Osmosis — paani ka diffusion, aksar Aquaporins ke zariye (ek facilitated channel).
Electrochemical Gradient — ions ke liye combined driving force.
Enzyme Kinetics — carrier saturation Michaelis–Menten logic use karta hai.
Membrane Potential — channels jaise K⁺ leak channels resting voltage set karte hain.
Phospholipid Bilayer — woh hydrophobic barrier jo proteins ko zaruri banata hai.