文档介绍：L1. Citric acid cycle
L2. Electron transport and oxidative hosphorylation
L3. Photosynthesis
Section L Respiration and Energy
Role
Location
The cycle
Energy yield
Regulation
Biosynthetic pathways
Citric acid cycle
Role
The citric acid柠檬酸cycle ,also known as the TCA (tricarboxylic acid三羧酸) cycle or Krebs cycle (after its discover in 1993), is used to oxidize the pyruvate formed during the glyco-lytic breakdown of glucose into CO2 and H2O. The cycle is a major energy source in the form of ATP and also produces precursors for many biosynthetic pathways.
Location
The citric acid cycle occurs within the mitochondria of eukaryotes and the cytosol of prokaryotes.
The cycle
Step 1 .Oxidation of fuel molecules to acetyl CoA
A major source of energy is glucose which is converted by glycolysis into pyruvate. Pyruvate dehydrogenase (plex of three enzymes and five coenzymes ) then oxidizes the pyruvate (using NAD+ which is reduced to NADH ) to form acetyl CoA and CO2 since the reaction involves both an oxidation and a loss of CO2, the process is called oxidative decarboxylation.
Acetyl-CoA
The cycle carries out the oxidation of acetyl groups from acetyl CoA to CO2 with the production of four pairs of electrons, stored initially in the reduced electron carriers NADH and FADH2
The citric acid cycle
Cycle mode
EIGHT STAGES
The citric acid cycle has eight stages:
(1)Production of citrate from oxaloacetate (草酰乙酸) and acetyl CoA (catalyzed by citrate synthase)
COOH CH3 CH2-COOH
CO + CO HO-C-COOH
CH2 S CH2-COOH
COOH CoA
Citrate formation