HUMAN BIOLOGY

62 Chapter 3

hoW much atp does cellular respiration

produce?

• From start to finish, cellular respiration typically nets thirty-six
  ATP for every glucose molecule.


• By far the most ATP is produced during the aerobic pathway that
  occurs in a cell’s mitochondria.

taKe-hoMe Message

summary of Cellular respiration

Figure 3.27 reviews the steps and ATP yield from cellular

respiration. Only this aerobic pathway delivers enough

energy to build and maintain a large, active, multicellular

organism such as a human. In many types of cells, the third

stage of reactions forms thirty-two ATP. When we add

these to the final yield from the preceding stages, the total

harvest is thirty-six ATP from one glucose molecule. This

is a very efficient use of our cellular resources!

While aerobic cellular respiration typically yields thirty-

six ATP, the actual amount may vary, depending on condi-

tions in a cell at a given moment—for instance, if a cell

requires a particular inter mediate elsewhere and pulls it

out of the reaction sequence. To learn more about this topic,

see Appendix I at the back of this book.

Figure 3.27 Animated! This diagram summarizes aerobic cellular respiration. (© Cengage Learning)

glucose

2 NADH 2 pyruvate

oxygen

8 NADH, 2 FADH 2

Typical net energy yield; 36 ATP

6 CO 2

4 ATP

(2 net)

2 ATP

Electron ChainTransport 32 ATP

Krebs

Cycle

2 ATP ATP

ATP

ATP

Glycolysis ATP

Cytoplasm

A The first stage, glycolysis, occurs in the cell’s cyto-

plasm. Enzymes convert a glucose molecule to 2 pyruvate

for a net yield of 2 ATP. During the reactions, 2 NAD+ pick

up electrons and hydrogen atoms, so 2 NADH form.

Mitochondrion

B The second stage, the Krebs cycle and a few steps

before it, occurs inside mitochondria. The 2 pyruvates

are broken down to CO 2 , which leaves the cell. During

the reactions, 8 NAD+ and 2 FAD pick up electrons and

hydrogen atoms, so 8 NADH and 2 FADH 2 form. 2 ATP

also form.

C The third and final stage, the electron transport chain,

occurs inside mitochondria. 10 NADH and 2 FADH 2 donate

electrons and hydrogen ions at electron transfer chains.

Electron flow through the chains sets up H+ gradients that

drive ATP formation. Oxygen accepts electrons at the end

of the chains.

3 .15

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