Respiration
During aerobic respiration, glucose is completely oxidized (all H’s removed) leaving CO2 as an endproduct. The H’s are taken by coenzymes (NAD and FAD) to the electron transport chain. There the energy is drained from the hydrogen electrons and the energy is used to make ATP. The H’s are ultimately accepted by O2 to make H2O as an endproduct.
Respiration occurs in three major stages:
1) Glycolysis – occurs in the cytoplasm for both prokaryotic and eukaryotic cells
• One glucose (6C) is broken into two 3C molecules – 2 pyruvic acids (pyruvate) • One oxidation step produces two molecules of reduced coenzyme – 2NADH • One step produces energy in the form of ATP – 2ATP • The pyruvic acids continue to the next stage – the Krebs Cycle • The 2 NADH proceed to the third stage – ETC • The 2 ATP are available to do cellular work
2) Krebs Cycle – occurs in the cytoplasm for prokaryotic cells and in the matrix of the mitochondria for eukaryotic cells
• Each pyruvic acid is completely oxidized in the Krebs Cycle to yield 3 CO2 • Five oxidation steps produce 4 molecules of reduced NADH and 1 molecule of reduced FADH2 • One step produces energy directly in the form of ATP(1 ATP
• Since glycolysis produces 2 pyruvic acids, the total endproducts of the Krebs cycle produced from the complete oxidation of both pyruvic acids is: 6CO2, 8NADH, 2FADH2, and 2ATP • The 6 CO2 are released as waste • The 8 NADH and 2 FADH2 proceed to the third stage – ETC • The 2 ATP are available for cell work
3) Electron Transport Chain (ETC) – in cell membrane for prokaryotic cells; in cristae of mitochondria for eukaryotic cells
• The high energy electrons taken from glucose by the coenzymes NAD and FAD are passed