Oxidative Phosphorylation

How are the electrons in NADH and FADH2 used to make ATP during cellular respiration?

Why?
The final phase of cellular respiration is oxidative phosphorylation. Both the electron transport chain
and chemiosmosis make up oxidative phosphorylation. During this phase of cellular respiration, all of the
that were produced in other phases of cellular respiration (glycolysis, the link
NADH and FADH2
reaction
, and Krebs cycle) are used to make ATP. The process occurs in the protein complexes
embedded in the inner mitochondrial membrane.

Model 1 – Electron Transport Chain

1. Consider the membranes illustrated in Model 1. Circle a section of the mitochondria below
where this site might be located

Oxidative phosphorylation

2. Refer to Model 1.
a. Describe the region in Model 1 where the highest concentration of hydrogen ion (H+) is
located.
- The highest concentration of hydrogen ions is located in the Intermembrane space.

b. According to Model 1, how do the hydrogen ions reach this area?

- The hydrogen ions go through a protein channels to get there

3. Explain why energy is required to move the hydrogen ions across the membrane in the direction
indicated in Model 1.

- Energy is required because it is moving through the membrane by protein channel and it needs
energy.

4. High potential energy electrons provide the energy necessary to pump hydrogen ions across
the inner mitochondrial membrane.
a. What molecules carry these high potential energy electrons?

- NADH, FADH2

b. Where did these electron acceptor molecules come from?

- They got it from the citric acid cycle.

c. When the electrons are released from the electron acceptor molecules, what else is produced?

- When electrons are released H+ ions are also produced

d. Is the release of an electron from one of these electron acceptor molecules oxidation
or reduction?

- Oxidation
 5. Refer to Model 1.
a. What molecule is the final electron acceptor after the electron has moved through the electron
transport chain?

- Oxidation

b. What compound is formed as a final product of the electron transport chain?

- H20/Water

6. Is any ATP produced in the electron transport chain?

- No

7. Is any ATP used in the electron transport chain?

- No

Model 2 – Chemiosmosis
 8. Describe the movement of hydrogen ions through the membrane illustrated in Model 2.

- The hydrogen ions move from the Intermembrane Space to the Mitochondrial Matrix.

9. Would free energy be required for the hydrogen ions to move in the direction shown in Model 2?
Explain your reasoning.

- No because it is going from high concentration to low concentration so no free energy is

required.

10. What is the name of the embedded protein that provides a channel for the hydrogen ions to pass
through the membrane?

- ATP Synthase

11. The flow of hydrogen ions through the protein channel provides free energy to do work. What
process in Model 2 requires energy?

- The synthesis of ATP

Read This!
The embedded protein complex, ATP synthase, is more of a machine than a chemical enzyme. Research
has shown that a protein “rotor” down the middle of the ATP synthase complex turns as hydrogen ions
flow through. This rotates other proteins, which then “squeeze” the ADP and inorganic phosphate
groups together to form ATP.

12. During oxidative phosphorylation, what molecule is being phosphorylated?

- ATP

13. Under ideal conditions each NADH molecule will result in three ATP molecules, and each
FADH2 molecule will result in two ATP molecules during oxidative phosphorylation. Calculate
the total number of ATP molecules that might be produced in this phase of cellular respiration
from one glucose molecule.

- Around 26-28 ATP

14. Considering all the stages of cellular respiration (glycolysis, link, Krebs cycle, and oxidative
phosphorylation) how many ATP molecules are produced from one glucose molecule, assuming
ideal circumstances?

- Around 38 ATP
 15. Because of its role in aerobic respiration, oxygen is essential for most living things on Earth. In
complete sentences, describe the role of molecular oxygen (O2) in aerobic respiration.
- Oxygen is an important electron acceptor in aerobic respiration.

16. Consider the overall chemical reaction for cellular respiration.

C6H12O6 + 6O2 ⎯→ 6CO2 + 6H2O
Complete the table below to identify the phase of cellular respiration where each of the
reactants are used, the products are produced, and the location in the cell where that phase
occurs. You may need to refer back to previous activities on cellular respiration.
Reactants Products

C6H12O6 6O2 6CO2 6H2O 38ATP

Phase(s) Used in Used in citric Produced Produced in Total produced

at glycolysis acid cycle and in the the electron in all the stages
which it Electron citric acid transport of cellular
is used transport chain cycle. chain.
respiration.
or
produced

Location Cytosol Matrix Matrix Inner Mitochondrion

mitochondrial
membrane

Extension Questions
17. Substrate level phosphorylation is the term used for phosphorylation that removes a
phosphate from one molecule and joins it to another molecule. Oxidative phosphorylation is the
term used for the attachment of free inorganic phosphate to a molecule. Identify the phases of
cellular respiration that use substrate level phosphorylation and that use oxidative phosphorylation.

- Glycolysis uses substrate level phosphorylation and the electron transport chain and
Chemiosmosis use oxidative phosphorylation.

18. Which side of the inner mitochondrial membrane would have a higher pH?

- The Intermembrane Space would have a higher pH.

19. During glycolysis the enzyme hexokinase uses ATP to transfer a phosphate to glucose to form
fructose-diphosphate. Suppose that a cell has only glucose available for energy and that the activity
of hexokinase is suddenly stopped. Explain in detail what is most likely to occur in the cell.

- Fructose-diphosphate won't be formed and glycolysis won't go on and pyruvate won't be

formed and cellular respiration won't occur.

20. Prokaryotic cells must have energy for cellular processes just like eukaryote cells do. Yet, they
have no mitochondria.
a. Which phase(s) of cellular respiration would be unaffected by the lack of mitochondria
in a cell?
- Glycolysis

b. The link reaction and Krebs cycle occur in the cytoplasm of prokaryotes in the same way that
they occur in the mitochondria of eukaryotes. However, a concentration gradient across a
membrane is a requirement of the electron transport chain. Propose an alternate site for this
phase of cellular respiration in prokaryotic cells.

- It would occur in the cell membrane.