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 CO2 and energy
 This energy is used to produce NADH and FADH2
 NADH and FADH2 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 CO2
 3 NADH
 1 FADH2
 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 energycarrying molecules?
From One Glucose
Glycolysis
2 pyruvate -->
2 acetyl-CoA
Citric acid cycle
ATP
2
Coenzymes
2 NADH
2
2 NADH
6 NADH
2 FADH2
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 H2O.
http://www.science.smith.edu/departments/Biology/Bio23
1/etc.html
C. Oxidative Phosphorylation and ATP
 Oxidative phosphorylation: the production of ATP
from ADP and Pi 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 FADH2, 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.