CHAPTER 23 Metabolism and Energy Production

What happens after glycolysis?  When oxygen is present (under aerobic conditions)…  The acetyl-CoA is sent into the citric acid cycle, which is followed by the electron transport chain. The latter process makes most of the ATP.

A. The Citric Acid Cycle  Overall, a series of reactions that degrade acetyl-CoA to CO 2 and energy  This energy is used to produce NADH and FADH 2 NADH and FADH 2 are the “electron limousines” that shuttle the electrons to the electron transport chain, where they are used to generate a lot of ATP.

Summary of Products: Citric Acid Cycle  You get… 2 CO 2 3 NADH 1 FADH 2 1 GTP which is used to form ATP  **These are the products from ONE acetyl-CoA. Double those numbers if you are considering the products from one glucose molecule through the whole process.

Citric Acid Cycle Regulation  Function of citric acid cycle: generate ATP  So, when the cell needs energy, pyruvate is converted to acetyl-CoA, and the citric acid cycle proceeds.  But when the cell has sufficient energy, there is not much conversion to acetyl-CoA, and the citric acid cycle slows.

B. Electron Carriers  What have we obtained so far in terms of energy- carrying molecules? From One GlucoseATPCoenzymes Glycolysis22 NADH 2 pyruvate --> 2 acetyl-CoA2 NADH Citric acid cycle26 NADH 2 FADH 2

How Do The Electron Carriers Work?  After glycolysis and the citric acid cycle, these carriers are in the reduced form.  As they are oxidized later on, they provide energy for the synthesis of ATP.  In the electron transport chain (which follows the citric acid cycle), electrons are passed from one intermembrane protein to the next until they combine with oxygen to form H 2 O. 1/etc.html

C. Oxidative Phosphorylation and ATP  Oxidative phosphorylation: the production of ATP from ADP and P i using the energy released during the electron transport chain  Chemiosmotic model links this energy to a proton gradient. As electrons are passed along the chain, H + is passed into the intermembrane space. A proton gradient is created, whereby the intermembrane space has both a positive charge and a lower pH. The energy generated by this gradient is used by ATP synthase to drive the synthesis of ATP.

Creation of Proton Gradient

D. ATP Energy from Glucose  How much ATP do you get from all of these processes?  ATP from glycolysis: 2 NADH (which, long-term, give you 4 ATP) + 2 ATP = 6 ATP  Conversion of pyruvate --> acetyl-CoA: 2 NADH (one per pyruvate) = 6 ATP  Citric acid cycle From each acetyl-CoA: 3 NADH, one FADH 2, one ATP which will, total, give 24 ATP  The combination of it all: 36 ATP per glucose.

Oxidation of Glucose

What Happens To All This Glucose?  If there is extra glucose around -- in excess of what our cells need for energy -- what happens to it?  If glucose levels in the brain or blood get low, what does the body do? Glucose can also be synthesized from non-carbohydrate sources as needed.