Acetyl-CoA and oxaloacetate combine to produce citric acid (or citrate) in the citric acid cycle. This is the first step in the cycle, also known as the condensation step.
Coenzyme A (CoA) escorts acetic acid produced from pyruvic acid into the first reaction of the citric acid cycle by forming acetyl-CoA. Acetyl-CoA is then used as a substrate in the first step of the citric acid cycle to produce citrate.
1. 6 carbon dioxide molecules combine with six 5-carbon molecules forming twelve 3-carbon molecules. 2. The 12 3-carbon molecules are converted into high-energy forms. 3. 2 of the 12 3-carbon molecules are removed and the plant uses them to produce sugars, lipids, amino acids, and other compounds. 4. The 10 3-carbon molecules change back into six 5-carbon molecules, which combine with 6 more carbon dioxide molecules. The process starts over.
The first step in using amino acids as a fuel is to break them down through a process called catabolism. This process involves breaking the amino acids down into smaller molecules that can be converted into energy through pathways such as the citric acid cycle and oxidative phosphorylation.
The two-carbon molecule that combines with a four-carbon molecule in the citric acid cycle to produce citric acid is acetyl-CoA. Acetyl-CoA condenses with oxaloacetate (a four-carbon molecule) to form citrate, the first step in the citric acid cycle.
RuBP
RuBP
RuBP
RuBP
RuBP
RuBP
RuBP
RuBP
RuBP
Carbon dioxide and RuBP combine to make PGA
RuBP
RuBP