Cellular Respiration and Electron Transport Chain

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Chapter 9: Cellular Respiration: Harvesting Chemical Energy
Overview: Before getting involved with the details of cellular respiration and photosynthesis, take a second to look at the big picture. Photosynthesis and cellular respiration are key ecological concepts involved with energy flow. Use Figure 9.2 to label the missing parts below.
See page 163 of your text for labeled figure.
Concept 9.1 Catabolic pathways yield energy by oxidizing organic fuels
1.

Explain the difference between fermentation and cellular respiration.
Fermentation is a partial degradation of sugars or other organic fuel that occurs without the use of oxygen.
Cellular respiration consumes oxygen as a reactant along with the organic fuel.

2.

Give the formula (with names) for the catabolic degradation of glucose by cellular respiration.
Organic Compounds + Oxygen  Carbon dioxide + Water + Energy

3.

Both cellular respiration and photosynthesis are redox reactions. In redox, reactions pay attention to the flow of electrons. What is the difference between oxidation and reduction?
In a redox reaction, the loss of electrons from one substance is called oxidation, and the addition of electrons to another substance is known as reduction.

4.

The following is a generalized formula for a redox reaction:

Xe– + Y  X + Ye–
Draw an arrow showing which component (X or Y) is oxidized and which is reduced.
Xe- is the reducing agent in this reaction, and Y is the oxidizing agent.
5.

When compounds lose electrons, they lose energy; when compounds gain electrons, they gain energy.

6.

In cellular respiration, electrons are not transferred directly from glucose to oxygen. Following the movement of hydrogens allows you to follow the flow of electrons. The hydrogens are held in the cell temporarily by what electron carrier? What electron carrier is hydrogen transferred to first?
NAD+

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7. The correct answer to question 6 is NAD+. It is a coenzyme. What is a coenzyme? What are coenzymes? (If you have forgotten, look back to a few pages in Chapter 8.)
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in metabolic reactions.
8.

Describe what happens when NAD+ is reduced. What enzyme is involved?
The enzymatic transfer of 2 electrons and 1 proton (H+) from an organic molecule in food to NAD+ reduces the NAD+ to NADH; the second proton (H+) is released. The enzyme involved is dehydrogenase.

9.

It is essential for you to understand the concept of oxidation/reduction and energy transfer. For the following pair, which molecule is the oxidized form, and which is reduced? Which molecule holds higher potential energy? Which is lower in potential energy?
NAD

Oxidized or Reduced?
Oxidized

Higher Energy/Lower Energy
Lower energy

NADH

Reduced

Higher energy

+

10. What is the function of the electron transport chain in cellular respiration?
The electron transport chain shuttles electrons down a series of redox reactions that release energy used to make ATP.
11. Electron transport involves a series of electron carriers.
Where are these found in eukaryotic cells? Membrane of the mitochondria
Where are these found in prokaryotic cells? Plasma membrane
12. What strongly electronegative atom, pulling electrons down the electron transport chain, is the final electron acceptor? Oxygen
13. Understanding the overall map of how cellular respiration works will make the details easier to learn. Use
Figure 9.6 to label the missing information in the figure that follows.
See page 167 in your text for the labeled figure.
14. Three types of phosphorylation (adding a phosphate) are covered in the text, and two of these occur in cellular respiration. Explain how the electron transport chain is utilized in oxidative phosphorylation.
This mode of ATP synthesis is powered by the redox reactions of the electron transport chain.

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15. The second form of phosphorylation is substrate level. Label the figure below to show the direct transfer of a phosphate from an organic substrate to ADP to form ATP.
See page 168 in your text for the labeled figure.
Concept 9.2 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
16. What is the meaning of glycolysis? What occurs in this step of cellular respiration?
Glycosis is a series of reactions that ultimately splits glucose into pyruvate. Glycolysis occurs in almost all living cells, serving as the starting point for fermentation or cellular respiration.
17. The starting product of glycolysis is the six-carbon sugar glucose, and the ending products are two threecarbon molecules of pyruvate.
The ten individual steps of glycolysis can be divided into two stages: energy investment and energy payoff.
These steps are shown in Figure 9.9, which details the enzymes and reactions at each of the ten steps. While you are not expected to memorize these steps and enzymes, you should study the figure carefully. The next few questions will help you focus your study.
18.

The figures below show a summary of glycolysis. Label the energy investment phase below and complete the figure. Then turn to Figure 9.9 on page 169 to find the two specific steps where ATP is used.
See page 168 in your text for the labeled figure.

19. The second step in glycolysis is the energy payoff phase. Label this phase and complete the figure. Note that it provides both ATP and NADH. Look at Figure 9.9 to locate the two steps where ATP is formed and the one step where NADH is formed.
See page 168 in your text for the labeled figure.
20. This final figure shows the net gain of energy for the cell after glycolysis. Most of the energy is still present in the two molecules of pyruvate. Complete the figure below to show the net energy gains.
See page 168 in your text for the labeled figure.
21. Notice that glycolysis occurs in the cystol of the cell. Is oxygen required? No
Concept 9.3 After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules 22. To enter the citric acid cycle, pyruvate must enter the mitochondria by active transport. Three things are necessary to convert pyruvate to acetyl CoA. Complete the missing parts of the chart below and then explain the three steps in the conversion process.
See page 170 in your text for the labeled figure.

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