Lecture: Krebs Cycle and Electron Transport Chain

Aerobic Respiration Krebs Cycle Glycolysis gets about 2% of the energy out of glucose, even with fermentation, 90% of the energy is still available in the form of compounds Oxygen is a powerful electron acceptor and is the key to unlocking more energy Glycolysis 1 6-C sugar + 2ATP 2 3-C sugars  2 Pyruvic Acids + 4ATP + 2NADH In the presence of oxygen Pyruvic acid enters the Krebs cycle 2 ATP O2 Glucose Glycolysis 2 Pyruvic Acid 4 ATP 2 NADH No O2 Alcohol Fermentation Lactic Acid Fermentation

Krebs Cycle

Summary of the Krebs Cycle Pyruvic acid is broken down into CO2 in a series of energy releasing steps Takes place in the mitochondria 1 atom of C from pyruvic acid becomes CO2 and is released into the air. NAD+ becomes NADH The other 2 atoms of C join Coenzyme A to form Acetyl Co-A 2-C Acetyl Co-A joins 4-C sugar to form Citric Acid (6-C compound, Coenzyme A is released) 6-C compound broken into a 5-C compound, releasing more CO2 and NADH 5-C compound broken into a 4-C compound, releasing more CO2, ATP and NADH 4-C compound turns back into 4-C sugar from step 5, releases FADH2 and NADH

Totals per 1 Glucose (so far) Anaerobic Respiration (Fermentation) Aerobic Respiration (Cellular Respiration) ATP = NADH = FADH2 = 2 4 2 10 2 Alcohol Fermentation Lactic Acid Fermentation 2 ATP No O2 Glycolysis 2 Pyruvic Acid Glucose 2 NADH 4 ATP O2 There is still a lot of energy left to be unleashed!

Aerobic Respiration (Cellular Respiration) So Why Do We Need O2? ATP is the energy that is readily used by cells Carrier molecules can be converted into ATP in the presence of oxygen! How? Another electron transport system (like photosynthesis) How many carrier molecules were formed in glycolysis and the Krebs cycle? There are 12 high energy molecules ready to be converted into ATP in the electron transport chain! Aerobic Respiration (Cellular Respiration) ATP = 4 NADH = 10 FADH2 = 2

Electron Transport Chain High energy electrons transferred from NADH and FADH2 into the electron transport chain Occurs in the inner membrane of the mitochondria As high energy e-s pass along the transport chain, H+ are transported into the intermembrane space An enzyme at the end combines low energy e-s with H+ and O2 to make water (this is why we need O2!) ATP synthase allows H+ out of the intermembrane space, and uses the energy to make ATP

So now how much ATP per Glucose? Each carrier molecule provided energy to make 2 to 3 ATP molecules FADH2 makes 2 NADH from glycolysis makes 2, NADH from Krebs cycle makes 3 Glycolysis Krebs Cycle Electron Transport Chain ATP = NADH = FADH2 = ATP already made = ATP from NADH = ATP from FADH2 = . Total = 2 2 4 28 2 8 2 4 36! That’s it for anaerobic!