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 energy-carrying molecules?

From One Glucose ATP Coenzymes

Glycolysis 2 2 NADH

2 pyruvate -->

2 acetyl-CoA 2 NADH

Citric acid cycle 2 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.

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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.