1. There are two types of reactions in metabolic pathways: anabolic and catabolic.
a. catabolic
b. anabolic
c. anabolic
d. catabolic
e. anabolic
f. anabolic
g. catabolic
h. catabolic, anabolic
2. Kinetic energy is associated with the relative motion of objects, whereas potential energy
refers to an object not presently moving; it is the energy that matter possesses because of its
location or structure.
3. Water behind a dam has potential energy. A mole of glucose also has potential energy,
although more specifically, glucose has chemical energy, a term used by biologists to refer to the
potential energy available for release in a chemical reaction.
4. Energy can be transferred and transformed, but it cannot be created or destroyed.
5. Every energy transfer or transformation increases the entropy in the universe. Although order
can increase locally, there is an unstoppable trend toward randomization of the universe as a
whole.
6. A process that occurs without an overall input of energy; a process that is energetically
favorable
7. Free energy is the portion of a system’s energy that can perform work when temperature and
pressure are uniform throughout the system, as in a living cell. Free energy is symbolized by the
letter G, after Professor Willard Gibbs.
8. An exergonic reaction proceeds with a net release of free energy. Because the chemical
mixture loses free energy, ΔG is negative for an exergonic reaction.
9. Cellular respiration is an exergonic reaction. The ΔG for this reaction is:
ΔG = – 686 kcal/mol (–2,870 kJ/mol)
10. Photosynthesis is an endergonic reaction. Plants get the required energy—686 kcal to make a
mole of glucose—from the environment by capturing light and converting its energy into
chemical energy.
11. ΔG must be negative.
12.
a. Chemical work, the pushing of endergonic reactions that would not occur spontaneously, such
as the synthesis of polymers from monomers
b. Transport work, the pumping of substances across membranes against the direction of
spontaneous movement; possible examples include the sodium-potassium pump and proton
pump
c. Mechanical work, such as the beating of cilia, the contraction of muscle cells, and the
movement of chromosomes during cellular reproduction
13. See page 149 of your text for the labeled figure.
a. Hydrolysis
b. ATP contains the sugar ribose, with the nitrogenous base adenine and a chain of three
phosphate groups bonded to it, forming adenosine triphosphate.
14. released.
ΔG = – 7.3 kcal/mol (–30.5 kJ/mol)
Exergonic
15. In cellular metabolism, energy coupling is the use of energy released from an exergonic
reaction to drive an endergonic reaction.
16. Phosphorylated intermediate
17. If ATP could not be regenerated by the phosphorylation of ADP, humans would use up
nearly their body weight in ATP each day.
18. A catalyst is a chemical agent that selectively increases the rate of a reaction without being
consumed by the reaction.
19. Activation energy is the amount of energy that reactants must absorb before a chemical
reaction will start; also called free energy of activation.
20. See page 153 of your text for the labeled figure.
a. An enzyme catalyzes a reaction by lowering the EA barrier.
b. Negative
c. It cannot make an endergonic reaction exergonic.
21. See page 154 of your text for the labeled figure.
enzyme: A macromolecule serving as a catalyst, a chemical agent that increases the rate of a
reaction without being consumed by the reaction. Most enzymes are proteins.
substrate: The reactant on which an enzyme works.
active site: The specific region of an enzyme that binds the substrate and that forms the pocket in
which catalysis occurs.
products: A material resulting from a chemical reaction.
22. Caused by entry of the substrate, induced fit is the change in shape of the active site of an
enzyme so that it binds more snugly to the substrate. In Figure 8.16 on page 154 of your text,
when the substrate enters the active site, it forms weak bonds with the enzyme, inducing a
change in the shape of the protein. This change allows additional weak bonds to form, causing
the active site to enfold the substrate and hold it in place.
23. Enzymes are proteins, and proteins are macromolecules with unique three-dimensional
configurations. The specificity of an enzyme results from its shape, which is a consequence of its
amino acid sequence. The specificity of an enzyme is attributed to a compatible fit between the
shape of its active site and the shape of the substrate.
24. a. In reactions involving two or more reactants, the active site provides a template on which
the substrates can come together in the proper orientation for a reaction to occur between them.
b. As the active site of an enzyme clutches the bound substrate, the enzyme may stretch the
substrate molecules toward their transition-state form, stressing and bending critical chemical
bonds that must be broken during the reaction.
c. The active site may also provide a microenvironment that is more conducive to a particular
type of reaction than the solution itself would be without the enzyme.
d. Direct participation of the active site in the chemical reaction is another mechanism of
catalysis.
25. The more substrate molecules that are available, the more frequently they access the active
sites of the enzyme molecules.
b. pH: With some exceptions, the optimal pH values for most enzymes fall in the range of pH 6–
8.
c. temperature: Up to a point, the rate of an enzymatic reaction increases with increasing
temperature, partly because substrates collide with active sites more frequently when molecules
move rapidly. Above that temperature, however, the speed of the enzymatic reaction drops
sharply.
26. Three-dimensional structures of proteins are sensitive to their environment. As a
consequence, each enzyme works better under some conditions than other conditions because
these optimal conditions favor the most active shape for their enzyme molecule.
27. Pepsin, found in the human stomach
28. A cofactor is any nonprotein molecule or ion that is required for the proper functioning of an
enzyme. Cofactors can be permanently bound to the active site or may bind loosely and
reversibly, along with the substrate, during catalysis. Examples of some cofactors are zinc, iron,
and copper in ionic form. Most vitamins are important in nutrition because they act as
coenzymes or raw materials from which coenzymes are made.