Topic 30: Citric Acid Cycle

Citric acid cycle

Acetyl-CoA enters the citric acid cycle, producing ATP, reduced electron carriers and CO2.

(1)

2 carbon molecule combines with 4 carbon molecule to make a 6 carbon molecule; CoA is removed; H2O added

(2)

Molecule converted into another form

(3)

6 carbon molecule converted to 5 carbon molecule; CO2 is lost (one carbon); NADH electron carrier produced

(4)

5 carbon molecule converted to 4 carbon molecule; CO2 is lost (one carbon); NADH electron carrier produced; CoA reintroduced

(5)

4 carbon molecule converted to another form; ATP produced; CoA lost

(6)

4 carbon molecule converted to another form; FADH2 electron carrier produced

(7)

4 carbon molecule converted to another form

(8)

4 carbon molecule converted to another form; electron carrier, NADH, formed

(9)

Final molecule same as molecule at beginning of cycle that joined with Acetyl-CoA

Approximate Total ATP Yield in Citric Acid Cycle

Look @ Table

The Citric Acid Cycle Intermediates…

can be important elsewhere in the cell

The citric acid cycle breaks apart an acetyl group into carbon molecules and energy storage molecules. Name these molecules and state how many of each are produced per acetyl-CoA.

Carbon molecules are:

• Carbon molecule is CO2. Two produced per Acetyl CoA

Energy storage molecules are:

• 3 NADH produced per Acetyl CoA

• 1 FADH2 produced per Acetyl CoA

• 1 ATP produced per Acetyl CoA

The citric acid cycle generates only one ATP as part of its chemical reactions and does so through substrate level phosphorylation. What then is the value of the citric acid cycle to the cell?

The value is in the generation of electron carriers that can be used to generate ATP through oxidative phosphorylation (or could say at the electron transport chain)

For each turn of the citric acid cycle, how many ATP are produced via substrate level phosphorylation? How many electron carriers and which type(s)?

ATP - 1

NAHD - 3

FADH2 - 1

Which carbon molecule enters the citric acid cycle from pyruvate oxidation? 

How many carbons does it have? 

In which molecule(s) do those carbons end up?

Acetyl CoA

2

Carbon dioxide

How many ATP are generated through substrate level phosphorylation and how many are generated through oxidative phosphorylation with electron carriers per acetyl-coA that enters the citric acid cycle?

2 ATP from substrate level phosphorylation for two acetyl coA

18 ATP from oxidative phosphorylation for two acetyl coA

OR

1 ATP from substrate level phosphorylation for one acetyl coA

9 ATP from oxidative phosphorylation for one acetyl coA