2.6.7
Glucose ek "battery pack" hai jo high-energy electrons se bhari hoti hai. Respiration ise ek saath nahi jalata — yeh electrons ko step by step strip karta hai aur unhe electron transport chain (ETC) ko deta hai, jo unhe use karke protons pump karta hai aur ATP banata hai. Isliye ATP ka total actually ek bookkeeping problem hai : directly-made (substrate-level) ATP gino, phir electron carriers (NADH, FADH₂) gino aur unhe unki "exchange rate" se ATP mein convert karo.
Definition Do tarike jinse cells ATP banati hain
Substrate-level phosphorylation : ek enzyme directly ek phosphate ko ADP par transfer karta hai. Poore ATP molecules ke roop mein count kiya jata hai.Oxidative phosphorylation : NADH/FADH₂ electrons ki energy proton pumping chalati hai; proton gradient ATP synthase ko power deta hai. Conversion factors ke zariye indirectly count kiya jata hai.
Poora trick yeh hai: har stage list karo, ATP, NADH, aur FADH₂ alag-alag tally karo, phir end mein carriers ko convert karo.
Intuition NADH ≠ FADH₂ ATP value mein kyunNADH apne electrons Complex I par dump karta hai, chain ki shuruat ke paas, isliye woh electrons teen proton-pumping complexes (I, III, IV) se guzarte hain. FADH₂ electrons Complex II par dump karta hai, jo protons pump nahi karta, isliye uske electrons Complex I ko skip karte hain aur sirf do pumps (III, IV) se guzarte hain. Kam protons pumped → kam ATP.
2.5 kyun, 3 kyun nahi? ATP synthase ko roughly 4 protons chahiye per ATP (3 rotor spin karne ke liye + 1 phosphate import karne ke liye). NADH ~10 protons pump karta hai → 10/4 = 2.5 6/4 = 1.5
Glycolysis (cytoplasm): glucose → 2 pyruvatePyruvate oxidation (mitochondrial matrix): 2 pyruvate → 2 acetyl-CoAKrebs / citric acid cycle (matrix): do baar run hota hai (ek per acetyl-CoA)Oxidative phosphorylation (inner membrane): carriers cash in karo
Stage
ATP (direct)
NADH
FADH₂
Glycolysis
+2
2
0
Pyruvate oxidation (×2)
0
2
0
Krebs cycle (×2)
2 (GTP)
6
2
Subtotal carriers 4 direct 10 NADH 2 FADH₂
Worked example Step 1 — Glycolysis bookkeepingGlycolysis glucose activate karne mein 2 ATP spend karta hai, phir substrate-level phosphorylation se 4 ATP banata hai → net +2 ATP . Yeh 2 NAD⁺ ko bhi reduce karta hai → 2 NADH .
Yeh step kyun? Humein net use karna hoga, gross nahi — woh 2 invested ATP ja chuke hain.
Worked example Step 2 — Pyruvate oxidationHar pyruvate CO₂ khota hai aur 1 NAD⁺ reduce karta hai. Do pyruvates → 2 NADH , 0 ATP, 0 FADH₂.
Yeh step kyun? Yeh do baar hota hai kyunki glycolysis ne humein do pyruvates diye. Yahan se hamesha ×2 karo.
Worked example Step 3 — Krebs cycle (per turn)Ek turn yield karta hai: 3 NADH, 1 FADH₂, 1 GTP (≈ATP) . Do turns → 6 NADH, 2 FADH₂, 2 ATP .
Yeh step kyun? GTP energetically ATP ke equivalent hai, isliye hum ise direct ATP count karte hain.
Intuition Shuttle wali catch (kyun kuch books 30 ya 36 kehti hain)Glycolysis mein bane 2 NADH cytoplasm mein stuck rehte hain. Unke electrons mitochondrion ke andar pohunchane ke liye ek shuttle use hota hai:
Malate–aspartate shuttle (heart, liver): electrons NADH ke roop mein rehte hain → poore 2.5 each → 32 total .Glycerol-phosphate shuttle (muscle, brain): electrons FADH₂ ko hand over ho jaate hain → sirf 1.5 each → 30 total (32 − 2 × 1 = 30
Isliye 30–32 modern range hai; 36–38 purana whole-number range hai.
Common mistake "Glycolysis 4 ATP banata hai, toh +4 likho."Yeh sahi kyun lagta hai: 4 ATP molecules sach mein produce hote hain. Fix: 2 shuru karne mein spend hue the; sirf net +2 hi total mein count hoga.
Common mistake "Krebs 3 NADH banata hai, toh cell ko 3 milte hain."Yeh sahi kyun lagta hai: cycle diagram ek turn mein 3 NADH dikhata hai. Fix: cycle ek glucose ke liye do baar run hoti hai (do acetyl-CoAs) → 6 NADH . ×2 bhool jaana #1 error hai.
Common mistake "NADH aur FADH₂ dono same ATP banate hain."Yeh sahi kyun lagta hai: dono electron carriers hain jo chain ko feed karte hain. Fix: FADH₂ baad mein enter karta hai (Complex II, koi proton pump nahi), isliye yeh kam yield karta hai (1.5 vs 2.5).
Common mistake "Answer hamesha 38 hota hai."Yeh sahi kyun lagta hai: yeh classic exam number hai. Fix: 38 3/2 conversion aur free shuttling assume karta hai. Modern biochem 30–32 deta hai. Jaano ki tumhara exam kaunsa model chahta hai.
Net ATP from glycolysis (direct) +2 ATP (4 bane − 2 invest kiye)
NADH produced in glycolysis per glucose 2 NADH
NADH + FADH₂ from pyruvate oxidation per glucose 2 NADH (0 FADH₂), kyunki yeh do baar run hota hai
Per single turn of Krebs cycle, the yield is 3 NADH, 1 FADH₂, 1 GTP
Total NADH and FADH₂ from Krebs per glucose 6 NADH, 2 FADH₂ (cycle do baar run hoti hai)
ATP per NADH and per FADH₂ (modern values) 2.5 ATP aur 1.5 ATP
Why FADH₂ yields less ATP than NADH Yeh Complex II par enter karta hai jo protons pump nahi karta, Complex I skip ho jaata hai
Total direct (substrate-level) ATP per glucose 4 (2 glycolysis + 2 Krebs GTP)
Modern total ATP per glucose 30–32 ATP (shuttle par depend karta hai)
Old textbook total ATP per glucose 36–38 ATP
Why malate-aspartate gives 32 but glycerol-phosphate gives 30 Glycerol-phosphate cytoplasmic NADH ko FADH₂ mein convert karta hai, har ek mein 1 ATP lose hota hai (total 2)
Why 2.5 and not 3 ATP per NADH ATP synthase ko ~4 H⁺ per ATP chahiye (phosphate import including); NADH ~10 H⁺ pump karta hai → 10/4 = 2.5
Recall Feynman: 12-saal ke bachche ko explain karoGlucose ek chocolate bar ki tarah hai jo energy se bhari hoti hai. Tumhara cell ise ek bite mein nahi khata — yeh choti-choti steps mein nibbles karta hai. Har nibble se chhote "energy delivery trucks" nikalte hain jise NADH aur FADH₂ kehte hain. Yeh trucks ek power station (electron transport chain) par jaate hain jo unhe use karke batteries (ATP) charge karta hai. Nibbling ke dauran seedhe kuch ATP batteries banti hain, lekin zyaadatar trucks se power station par banti hain. Directly bani batteries gino, trucks gino aur dekho ki har truck kitni batteries khareedta hai (NADH 2.5 khareedta hai, FADH₂ 1.5 khareedta hai), sab add karo — ek chocolate bar se roughly 30 se 32 batteries!
"2 - 2 - 2, phir 6 - 2 - 2"
Glycolysis: 2 ATP, 2 NADH, (0 FADH₂).
Pyruvate ox: 2 NADH.
Krebs: 6 NADH, 2 FADH₂, 2 ATP.
Carriers: 10 NADH, 2 FADH₂ → ×2.5 aur ×1.5 → +28 → 32 total .
2.5 ATP each via Complex I
1.5 ATP each via Complex II
Glycolysis: +2 ATP, 2 NADH
Krebs cycle x2: 2 ATP, 6 NADH, 2 FADH2
Oxidative phosphorylation
