The Kreb’s Cycle and Electron Transport Chapter 9 Cellular Respiration

Kreb’s Cycle Introduction At end of glycolysis, about 90% of the chemical energy that was available in glucose is still unused To extract that energy, stored in pyruvic acid, the cell turns to one of the world’s most powerful electron acceptors------oxygen Oxygen is required for the final steps of cellular respiration

Kreb’s Cycle Introduction Since the Kreb’s Cycle requires oxygen, it is said to be AEROBIC Kreb’s Cycle Second Stage of Cellular Respiration Takes place in the mitochondria Process by which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions Also known as the Citric Acid Cycle

Kreb’s Cycle Steps of the Kreb’s Cycle: 1) Begins with the pyruvic acid molecules being broken down as follows Pyruvic Acid→CO2 & Acetyl-CoA→Citric Acid Carbon Dioxide is a waste product 2)Citric acid is then broken down into a 5-carbon compound and then into a 4 carbon compound 4-carbon compound started the process by binding with Acetyl-CoA to form Citric Acid

ATP and Waste Products Every time you exhale, you release the carbon dioxide produced in the Kreb’s cycle 1 molecule of ATP is formed for every 1 cycle (net ATP in Kreb’s cycle is 2) Cycle produces many electron carriers (NADH and FADH2) which are sent off to the electron transport chain to make the remaining ATP

Electron Transport Chain 3rd stage of cellular respiration Uses NADH (Glycolysis and Kreb’s cycle) and FADH2 (Kreb’s cycle) to convert ADP into ATP Occurs in the mitochondria

Electron Tranport Chain Steps of ETC: 1) High energy electrons from NADH and FADH2 are passed along the ETC. 2) High energy electrons are removed leaving NAD+ and FAD. 3) High energy electrons pass hydrogen atoms across the membrane. These hydrogen atoms bind with oxygen to form water

Electron Transport Chain Steps of ETC (cont): 4) As the hydrogen atoms escape through an ATP synthase channel, the energy from the electrons is used to bind an ADP to a phosphate to form ATP Every NADH forms 3 ATP Every FADH2 forms 2 ATP

Electron Transport Totals 10 NADH (2 from glycolysis and 8 from Kreb’s cycle) nets 30 ATP 2 FADH2 (from Kreb’s Cycle) nets 4 ATP Total ATP in ETC=34 ATP Water is also released during ETC

Efficiency of Cellular Respiration Efficiency of respiration is 7.3 kcal/mole x 38 ATP/glucose/686 kcal/mole glucose = 40%. The other approximately 60% is lost as heat.