Recall Feynman: 12-saal ke bachche ko explain karo
Socho tumhare cell mein ek chota sa merry-go-round hai. Tum uspe ek chota 2-tukda snack (acetyl-CoA) daaldo. Jab yeh ek poora loop spin karta hai, machine energy sparks rip off karta hai aur unhe NADH aur FADH₂ naam ke chote battery-trucks pe clip karta hai. Yeh do bits of smoke bhi phoonkta hai (CO₂) — wahi hawa hai jo tum bahar exhale karte ho! Loop ke end mein merry-go-round phir se khali ho jaata hai, agले snack ke liye taiyaar. Battery-trucks phir ek alag factory ki taraf jaate hain jo un sparks ko bahut saari asli energy (ATP) mein badal deta hai.
What is the true fuel input of the Krebs cycle?
Acetyl-CoA (2 carbons), not glucose.
What 4C molecule does acetyl-CoA combine with to start the cycle?
Oxaloacetate (forming citrate).
How many CO₂ are released per turn of the Krebs cycle?
2 CO₂.
How many NADH per turn of the Krebs cycle?
3 NADH.
How many FADH₂ per turn?
1 FADH₂.
How many ATP (substrate-level) per turn?
1 ATP (or GTP).
Per glucose, how many times does the Krebs cycle run, and why?
Twice, because glucose yields 2 pyruvate → 2 acetyl-CoA.
Total Krebs outputs per glucose?
4 CO₂, 6 NADH, 2 FADH₂, 2 ATP.
Why is the Krebs cycle called a "cycle"?
Oxaloacetate is regenerated, so it returns to its start to run again.
Is O₂ directly used in the Krebs cycle reactions?
No; O₂ is used in the ETC. The cycle stops without O₂ because NAD⁺/FAD can't be recycled.
What is the main purpose of the Krebs cycle?
To load electron carriers (NADH, FADH₂), not to make ATP directly.
Where are the 6 CO₂ per glucose released?
2 in the link reaction, 4 in the Krebs cycle (2 per turn × 2).
