Biology, Eighth Edition (Raven)

Chapter 7: How Cells Harvest Energy

How the NAD+ Works

Why are oxidation and reduction important in cellular respiration? Reduction-oxidation (redox) reactions are important in cellular respiration and other biochemical pathways because redox reactions are a good way to transfer energy from one molecule to another. Reduction is the addition of an electron while oxidation is the removal of an electron. As described in the animation, hydrogen atoms are frequently transferred along with their electrons. Bonds between hydrogen and carbon atoms share electrons equally between the molecules. Bonds between oxygen and hydrogen share electrons unequally, the electrons are much more closely associated with the oxygen. This is a lower energy state.

When wood or gasoline is burned oxygen gas (O2) reacts with the carbon-hydrogen rich molecules. Heat is released and carbon dioxide and water are produced. This is similar to, but much less controlled than, the process of cellular respiration. NAD+ acts as an intermediary, oxidizing the food molecules in a much more controlled fashion. By using NAD+ and the electron transport chain the oxidation of organic molecules can be linked to the production of ATP rather than just the generation of heat.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

Cells obtain energy by ________ food molecules such as glucose.
A)reducing
B)oxidizing
C)redoxing
D)anabolizing
E)phosphorylating
2.

Which of the following best describers the reduction of the coenzyme NAD?
A)NAD + H -> NADH
B)NAD+ + H -> NADH
C)NAD+ + H -> NADH2
D)NADH -> NAD+ + H
E)NADH -> NAD + H
3.

A hydrogen atom consists of
A)protons only.
B)electrons only.
C)a proton and an electron.
D)a proton and several electrons.
E)a variable number of protons and electrons.
4.

Whenever a molecule is oxidized, another molecule must be reduced.
A)True
B)False
5.

NADH serves as an electron carrier that can donate its hydrogen to other molecules.
A)True
B)False
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