Describe photophosphorylation (cyclic and non-cyclic)

2.7.6 · Biology › Photosynthesis

YEH HAI KYA? (Definition)

PLANTS KO ATP AUR NADPH DONO KI ZAROORAT KYU HAI?

NON-CYCLIC KAISE KAAM KARTA HAI — step by step (Z-scheme)

Figure — Describe photophosphorylation (cyclic and non-cyclic)

Worked example Electron ko non-cyclic flow mein walk karana

Step 1 — Light PSII (P680) se takrati hai. Ek electron high energy level par excite ho jaata hai. Yeh step kyun? Light energy ek excited electron ki energy ke roop mein capture hoti hai — baaki sab wahi energy hai jo usefully release ho rahi hai.

Step 2 — Water split hota hai (photolysis). $2 H_{2} O \to 4 H^{+} + 4 e^{-} + O_{2}$ . Release hue electrons woh replace karte hain jo PSII ne lose kiye the. Yeh step kyun? PSII ne abhi-abhi ek electron diya; use refill karna padega warna woh dobara fire nahi kar sakta. Water electron source hai — aur O₂ woh by-product hai jo hum breathe karte hain.

Step 3 — Electron carriers ke through travel karta hai (plastoquinone → cytochrome b₆f → plastocyanin). Jaise-jaise yeh energy mein drop karta hai, H⁺ thylakoid lumen mein pump hote hain. Yeh step kyun? "Downhill" energy waste nahi hoti — yeh ek proton gradient banati hai (chemiosmosis).

Step 4 — Light PSI (P700) se takrati hai. Ab lower-energy wala electron re-excite ho jaata hai. Yeh step kyun? Ise raaste mein energy loss hui thi; ek doosra photon ise itna "re-lift" karta hai ki woh NADP⁺ ko reduce kar sake.

Step 5 — NADP⁺ reduce hota hai. $N A D P^{+} + 2 e^{-} + H^{+} \to N A D P H$ . Yeh step kyun? Yeh electron ka final destination hai — NADPH Calvin cycle mein reducing power le jaata hai.

Step 6 — ATP synthase. H⁺ apne gradient ke neeche lumen se bahar ATP synthase ke through flow karte hain → $A D P + P i \to A T P$ . Yeh step kyun? Stored gradient energy ATP ke roop mein cash in hoti hai. Yeh coupling chemiosmosis hai.

CYCLIC KAISE KAAM KARTA HAI

Derivation: ATP energy actually aati kahan se hai?

Formula Chemiosmotic free energy (first principles)

Har mole H⁺ ke membrane ke paar move hone par stored energy (proton-motive force) ke do parts hain — ek concentration part aur ek electrical part: $Δ G = R T ln \frac{[ H ^{+} ] _{in}}{[ H ^{+} ] _{o u t}} + z F Δ ψ$ Build-up:

Ek solute ko concentration ratio ke against move karna $R T ln (ratio)$ cost karta hai — standard chemical potential.
H⁺ charge $z = + 1$ carry karta hai, isliye ise voltage $Δ ψ$ ke paar move karna $z F Δ ψ$ cost karta hai (work = charge × voltage). $p H = - lo g_{10} [H^{+}]$ use karke aur $ln \to 2.303 lo g$ convert karke: $Δ G = - 2.303 R T Δ p H + F Δ ψ$ Yeh kyun matter karta hai: ek bada $Δ p H$ (lumen acidic, stroma alkaline) energy store karta hai. ATP synthase is $Δ G$ ko release karta hai $A D P + P i \to A T P$ ( $+ 30.5$ kJ/mol) drive karne ke liye. Approximately 3–4 H⁺ per ATP pass hote hain kyunki ek ATP ko ek H⁺ se zyada energy chahiye.

Ek nazar mein compare karo

Feature	Non-cyclic	Cyclic
Use hone wale Photosystems	PSII + PSI	PSI only
Electron path	Linear (open)	Loop (closed)
Water split?	Haan	Nahi
O₂ release?	Haan	Nahi
NADPH banta hai?	Haan	Nahi
ATP banta hai?	Haan	Haan
Electron source	Water	Wahi electron (recycled)

Common mistake Common errors ko steel-man karna

Galti 1: "Cyclic flow bhi NADPH banata hai." Kyun sahi lagta hai: dono pathways mein PSI involve hai aur ATP produce hota hai, isliye yeh symmetric lagta hai. Fix: Cyclic flow mein electron ko chain par wapas bheja jaata hai NADP⁺ ki jagah. Koi final electron acceptor nahi → koi NADPH nahi. Sirf ATP.

Galti 2: "Water splitting PSI par hoti hai." Kyun sahi lagta hai: PSI "Photosystem One" hai, isliye lagta hai ki yeh pehle hona chahiye. Fix: Numbering discovery order se hai, flow order se nahi. Z-scheme mein electron PSII → PSI jaata hai, aur water PSII par split hoti hai.

Galti 3: "ATP directly photosystems dwara banta hai." Kyun sahi lagta hai: light → ATP seedha lagta hai. Fix: ATP ATP synthase dwara banta hai, jo proton gradient se drive hota hai — light sirf gradient banati hai. Yeh indirect step chemiosmosis hai.

Galti 4: "O₂ CO₂ se aati hai." Fix: Photosynthesis mein release hone wali O₂ water (photolysis) se aati hai, CO₂ se nahi — isotope (¹⁸O) labelling se prove kiya gaya hai.

Recall Feynman: ek 12-saal ke bachhe ko samjhao

Ek water slide imagine karo. Tum seedhi chadh jaate ho (woh light hai jo ek electron ko energy deti hai). Tum slide se neeche whoosh karte ho aur jis paani ko tum push karte ho woh ek chota water-wheel ghoomta hai (woh wheel = ATP synthase jo ATP banata hai). Phir tumhare paas do choices hain: (A) Non-cyclic — tum wapas nahi chadhte; ek dost paani ki bucket se (split water molecule) neeche tumhari jagah le leta hai, aur tum ek parcel (NADPH) deliver karne kitchen (Calvin cycle) mein chale jaate ho. Bucket mein se ek hawa ka bubble bhi nikalta hai — wahi oxygen hai jo tum breathe karte ho. (B) Cyclic — tum ek rope pakad lete ho aur seedha usi slide ke upar wapas swing karte ho aur dobara jaate ho, sirf wheel ko zyada ATP ke liye ghoomte rehne ke liye. Koi bucket nahi chahiye, koi hawa ka bubble nahi, koi parcel nahi. Toh: cyclic = sirf ATP; non-cyclic = ATP + parcel + oxygen.

Flashcards

Photophosphorylation mein ATP banane ke liye kaun se do molecules combine hote hain?

ADP + inorganic phosphate (Pi)

Chloroplast mein photophosphorylation kahan hota hai?

Thylakoid membrane mein

Non-cyclic photophosphorylation mein kaun se photosystems use hote hain?

PSII aur PSI

Cyclic photophosphorylation mein kaun sa photosystem use hota hai?

Sirf PSI

Non-cyclic photophosphorylation ke products kya hain?

ATP, NADPH, aur O₂

Cyclic photophosphorylation ka ek-maatra product kya hai?

ATP

Kaun se photosystem mein water split hoti hai (photolysis)?

PSII (P680)

Photosynthesis mein release hone wali O₂ ka source kya hai?

Water (photolysis ke zariye), ¹⁸O labelling se prove kiya gaya

Cyclic pathway NADPH kyun nahi banata?

Electron NADP⁺ reduce karne ki jagah chain par wapas loop karta hai

ATP synthase ko directly kya drive karta hai?

Thylakoid membrane ke paar proton (H⁺) gradient (chemiosmosis)

Plants non-cyclic ke saath cyclic flow kyun chalate hain?

Calvin cycle ke liye extra ATP banane ke liye bina extra NADPH banaye

Water ke photolysis ka equation kya hai?

2H₂O → 4H⁺ + 4e⁻ + O₂

Non-cyclic flow mein final electron acceptor kya hai?

NADP⁺ (NADPH ban jaata hai)

P680 aur P700 dwara absorb ki jaane wali wavelengths?

680 nm (PSII) aur 700 nm (PSI)

Cytochrome b₆f aur PSI ke beech carrier ka naam batao.

Plastocyanin

Connections

Light Dependent Reactions
Z-Scheme of Electron Transport
Chemiosmosis and ATP Synthase
Photolysis of Water
Calvin Cycle — woh customer jo ATP & NADPH use karta hai
Oxidative Phosphorylation — mitochondria mein same chemiosmotic principle
Chloroplast Structure