Cellular Respiration

1. Glycolysis
• does not require oxygen and does not take place in mitochondria
• takes place in cytoplasm (cytosol) 
• glucose: C6H12O6 --> two 3-carbon glucose molecules
• called glyceraldehyde 3-phosphate
• the breaking of glucose creates energy, which is transferred to ATP and NADH
• NADH holds small amounts of energy, later to be turned into ATP
• overall products: 2 pyruvate, 2 ATP, and 2 NADH
• 4 ATP were produced, but 2 were used on making glycolysis start. 
2. Fermentation
• anaerobic respiration: without oxygen
3. The Krebs Cycle
• in mitochondria, pyruvate is broken apart and combined with coenzyme (CoA) to form 2-carbon molecule, Acetyl CoA
• single atom of carbon is lost as carbon dioxide (byproduct) 
• energy released is stored in 2 NADH
• combines each Acetyl CoA with four-carbon carries molecule to make 6-carbon molecule of citric acid
• citric acid is carried through a series of chemical reactions, creating NADH, carbon dioxide, FADH2, and GTP (precursor for ATP) 
• overall: 2 ATP, 6 NADH, 2 FADH2
• glucose is completely broken down
4. Electron transport chain
• FADH and NADH give high-energy electrons to energy carrier molecules in membrane of mitochondria
• when passing from carrier to carrier, lost energy is used to pump hydrogen ions into intermembrane space
• hydrogen ions flow "down" the chain, and go out through ATP synthase channel, which transfers energy to ATP.
5. Post-electron transport chain
• low-energy electrons and hydrogen ions combine with water to form oxygen
• oxygen drives ATP-producing reactions by accepting "spent" hydrogens
• overall: 38 ATP from cellular respiration