Final answer:
The Krebs cycle starts with citric acid combining with oxaloacetic acid, followed by conversion to cis-aconitic acid, then to isocitric acid, α-ketoglutarate, succinic acid, fumaric acid, and malic acid, before regenerating oxaloacetic acid.
Step-by-step explanation:
Order of Steps in the Krebs Cycle
The Krebs cycle, also known as the citric acid cycle or TCA cycle, is a series of chemical reactions used by all aerobic organisms to generate energy. When arranging the steps of the Krebs cycle starting with citric acid, we follow these steps in order:
Citric acid (B) - Starts the cycle by combining with oxaloacetic acid.
Cis-aconitic acid (H) - Citric acid is converted to cis-aconitic acid through a dehydration step.
Isocitric acid (C) - Cis-aconitic acid is hydrated to form isocitric acid.
Ketoglutaric acid (D) - Isocitric acid is oxidized, releasing CO2, and yielding α-ketoglutarate.
Succinic acid (F) - After another CO2 release and reduction of NAD+ to NADH, α-ketoglutarate is converted to succinic acid.
Fumaric acid (E) - Succinic acid is oxidized to fumaric acid, producing FADH2.
Malic acid (G) - Fumaric acid is hydrated to malic acid.
Oxaloacetic acid (A) - Malic acid is oxidized to regenerate oxaloacetic acid, allowing the cycle to continue.
In this cyclical process, energy is captured in the form of ATP, and electron carriers NADH and FADH2 are produced, which are later used in the electron transport chain to generate a larger amount of ATP.