Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 8 (p. 158)

1. An anabolic reaction synthesizes products with energy; a catabolic reaction breaks down products with an accompanying release of energy.

2. Oxidation occurs when a molecule loses an electron; reduction is when a molecule gains an electron. These two must occur together because every electron that is lost by one molecule must be gained by another.

3. The First Law of Thermodynamics states that energy can be changed from one form to another (potential to kinetic) but can’t be lost or gained. The Second Law of Thermodynamics states that entropy increases, where entropy is energy so random and dissipated that it can’t be used for work.

4. Heat is the energy of random molecular motion. Entropy is a tendency toward disorder in the universe. Free energy present in the chemical bonds of a molecule, minus the energy lost to entropy.

5. In exergonic reactions, products contain less energy or more disorder than the reactants, release energy, and proceed spontaneously. In endergonic reactions, products contain more free energy or more disorder than reactants and require an input of energy to proceed.

6. Activation energy is the energy required to get spontaneous reactions going. Catalysts lower the activation energy required for a reaction to get started and will provide for a greater amount of reactant converted into product.

7. Enzymes typically function at an optimum range of temperature. Above or below this range the reaction may be slowed or halted altogether if the protein (enzymes are proteins) becomes denatured. When an enzyme is denatured, it unfolds and loses its catalytic ability.

8. The active site on an enzyme is where the substrate binds. An allosteric site is where a non-competitive enzyme inhibitor would bind, effecting a change in the shape of the enzyme so that it could no longer bind the substrate.

9. The high-energy bonds between the phosphate groups liberate the most energy when they are cleaved. Cleaving those bonds liberates 7.3 kcal of energy, which represents about twice the activation energy of most cellular reactions.

10. A sequential series of reactions inside a cell is called a biochemical pathway. The final reactions are thought to have evolved first because pathways evolve backward, adding new steps at the beginning. The mechanism for providing the feedback regulation is the binding of the product to the allosteric site of the enzyme.