Key Concepts for Chapter 9

These are the most important concepts you are learning in this chapter:

1. Metabolism, the sum total of all chemical reactions occurring in the cell, can be divided into catabolism and anabolism. In catabolism, molecules are reduced in complexity and free energy is made available. Anabolism involves the use of free energy to increase the complexity of molecules.

2. During catabolism, nutrients are funneled into a few common pathways for more efficient use of enzymes ( a few pathways process a wide variety of nutrients).

3. The tricarboxylic acid cycle is the final pathway for the aerobic oxidation of nutrients to CO₂.

4. The majority of energy released in catabolism is generated by the movement of electrons from electron transport carriers with more negative reduction potentials to ones with more positive reduction potentials. Thus aerobic respiration is much more efficient than anaerobic catabolism.

5. A wide variety of electron acceptors can be used in catabolism: O₂ (aerobic respiration), organic molecules (fermentation), and oxidized inorganic molecules other than O₂ (anaerobic respiration). Furthermore, reduced inorganic molecules as well as organic molecules can serve as electron donors for electron transport and ATP synthesis. Microbial catabolism is unique in the diversity of nutrients and mechanisms employed to make energy available.

6. In photosynthesis trapped light energy boosts electrons to more negative reduction potentials or higher energy levels. These energized electrons are then used to make ATP and NADPH or NADH during electron transport.

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