Chapter 6 Review
Metabolism: Energy & Enzymes
Living things can't exhibit any of the
A metabolic pathway is a series of
characteristics of life without a supply of
reactions that proceed in an orderly, step-byenergy. There are two energy laws that are basic
step manner. Each reaction has a specific
to understanding energy-use patterns in
enzyme that speeds the reaction by forming a
organisms at the cellular level. The first law
complex with its substrates. Formation of the
says that energy cannot be created or destroyed,
enzyme-substrate complex lowers the energy of
but can only be transferred or transformed. The
activation, the amount of energy required to
second law states that a usable form of energy
activate the reactants. Any environmental factor
cannot be converted completely into another
that affects the shape of a protein also affects
usable form. As a result of these laws, we know
the ability of an enzyme to do its job. (Many
that the entropy (disorder) of the universe is
enzymes have cofactors or coenzymes that
increasing and that only a constant input of
help them carry out a reaction.)
energy maintains the organization of living
Photosynthesis, which transforms solar
things.
energy
to
chemical
energy
within
carbohydrates, is a metabolic pathway that
Metabolism is all the reactions that occur in
occurs in chloroplasts. Reduction is the gain of
a cell. Only those reactions that result in a
hydrogen atoms (H+ + e-). During photosynthenegative free energy difference—that is, the
sis, carbon dioxide is reduced to glucose, a
products have less usable energy than the
carbohydrate. Cellular respiration, which is
reactants—occur spontaneously. Such reactions,
completed in mitochondria, is a metabolic
called exergonic reactions, release energy.
pathway that transforms the energy of glucose
Endergonic reactions, which require an input of
(usually) into that of ATP molecules. Oxidation
energy, occur because it is possible to couple an
is the loss of hydrogen atoms. During cellular
exergonic process with an en-dergonic process.
respiration, carbohydrate is oxidized to carbon
For example, glucose breakdown is an exergonic
dioxide and water. There is a cycling of
metabolic pathway that drives the buildup of
molecules
between
chloroplasts
and
many ATP molecules. These ATP molecules
mitochondria, but energy flows one way. Eventhen supply energy for cellular work. Thus, ATP
tually, all the solar energy captured by plants is
goes through a cycle in which it is constantly
lost as heat as ATP is utilized by cells.
being built up from, and then broken down to,
ADP + P.
Study the text section by section. Answer the study questions so that you can fulfill the learning objectives
for each section.
6.1. Metabolic Reactions and Energy Transformations
The learning objective for this section is:
 Explain the two laws of thermodynamics.
1. Indicate whether these statements, related to the energy laws, are true (T) or false (F), and if
the statements are false, change them to true statements:
a.
The chemical energy of ATP cannot be transformed into any other type of energy such as
kinetic energy. Rewrite:
b.
A cell produces ATP, and therefore cells do not obey the first law of thermodynamics.
Rewrite:
c.
Because energy transformations always result in a loss of usable energy, the entropy of the
universe is increasing. Rewrite:
d.
Because our society uses coal as an energy source, it is helping to decrease the entropy of the
universe. Rewrite:
6.2. Metabolic Reactions and Energy Transformations
The learning objectives for this section are:
 Compare exergonic and endergonic reactions.
 Explain the cycle of ATP buildup and ATP breakdown.
2. Place the appropriate letters next to each statement.
En—endergonic Ex—exergonic
a. ___ Energy is released as the reaction occurs.
b. ___ Energy is required to make the reaction go.
c. ___ Reaction used by the body for muscle contraction and nerve conduction.
d. ___ ATP  ADP + P.
e. ___ ADP + P  ATP.
3. Label this diagram, using these terms: ATP
ADP
P (used twice)
b. ________
c. __________
a. ________
__
d. ________
__
4. Label each of the following as pertaining to the left (L) or right (R) side of the diagram in
question 3. Explain your choice.
a.
_cellular respiration. Explain:
b.
_muscle contraction. Explain:
c.
_active transport. Explain:
5. ATP is the common a. ____________________of cells; when cells require energy, they
"spend" ATP. ATP breakdown provides energy for b_____________ work, such as synthesizing
macromolecules; c___________________ work, such as pumping substances across plasma
membranes; and d_______________ work, such as the beating of flagella. Because ATP
breakdown is e_______________ to endergonic reactions, energy transformation occurs with
minimal loss to the cell.
6.3. Metabolic Pathways & Enzymes
The learning objectives for this section are:
 Define metabolic pathway.
 Explain why enzymes speed reactions.
 Explain how environmental factors affect the activity of enzymes, and give
examples.
 Describe the functions of cofactors and coenzymes.
6. Consider the following diagram of a metabolic pathway:
E1
A
E2
E3
E4
E5
B  C  D  E 
E6
F  G
Use the following terms in the blanks: enzymes, products, reactants.
A-F are a______________, and B-G are b_____________. E1-E6 are c_______________.
A is a d_______________ for the first enzyme, and B is the product.
7.
Label this diagram using the following alphabetized list of phrases. You will use each phrase
twice.
energy of activation
energy of product
energy of reactant
8. Label this diagram, using the following alphabetized list of terms.
active site
enzyme (used more than once)
enzyme-substrate complex
products
substrate
9. Which portion of the diagram in question 8 pertains to enzymes lowering the energy of
activation? a_____________________
Why? b________________________________________________________________
10. Express the reaction in question 8 in equation form, using E (for enzyme), S (for substrate), and
P (for product}. a- ______________________________________________________________
Is the reaction shown in question 8 a synthetic reaction or a degradative reaction? b___________
How do you know? c_____________________________________________________________
The enzyme-substrate complex and the reaction occur at the d ________________________ site of
the enzyme.
What is the significance of using the label “enzyme” twice in the diagram in question 8? It shows
that e __________________________________________________________________________
Why are enzymes named for their substrates (e.g., maltase speeds the breakdown of maltose)?
f
_____________________________________________________________________
11. Complete each statement with the term increases or decreases.
Raising the temperature generally a____________________ the rate of an enzymatic reaction.
Boiling an enzyme drastically b______________________ the rate of the reaction.
Changing the pH toward the optimum pH for an enzyme c_________________ the rate of the
reaction.
Introducing a competitive inhibitor d_______________________the availability of an enzyme for
its normal substrate.
Due to feedback inhibition, the affinity of the active site for the substrate e ___________________.
12. Enzymes have helpers called a_____________________whi ch b________________
_________________________________________________________________________
6.4. Oxidation Reduction and the Flow of Energy
The learning objective for this section is:
 Compare the equations for photosynthesis and cellular respiration.
13. Oxidation is defined as the a _______________________(gain/loss) of electrons, and
reduction is defined as the b _______________________ (gain/loss) of electrons. Therefore,
in living things, hydrogen ions often accompany electrons. Therefore in living things,
oxidation is the c___________________________ of d ______________________ atoms, and
reduction is the e __________________ of f __________________atoms.
14. An overall equation for photosynthesis, a metabolic pathway in plant cells, is
Energy + 6 CO2 + 6 H20  C6H12O6 + 6 O2
Carbon dioxide
water
glucose
oxygen
In this equation a __________________________________ molecules are oxidized, releasing
b
______________________ molecules to the air. c ______________________ is reduced
and becomes d ______________________. e ______________________ drives this reaction.
15. An overall equation for cellular respiration is
C6H12O6 + 6 O2  6 CO2 + 6 H20 + Energy
glucose
oxygen
Carbon dioxide
water
In this equation a __________________________________ is oxidized, and
b
______________________ is released to the air. c ______________________ is reduced to
d
______________________, a low energy molecule. The oxidation of glucose makes energy
available for the production of e ______________________ molecules.
16. Show that there is a cycling of matter by completing this diagram using these terms:
H2O and CO2 (used twice) O2 and C6H1206
a. _____________
chloroplasts  b. ____________
mitochondria  c. ___________
cycling
17. Show that there is a flow of energy through living things by completing this diagram using these
terms: heat ATP solar energy glucose
a. _____________ chloroplasts produce  b. ______________ mitochondria produce  c. ___________
(in plants)
(in all organisms)
d. _________
18. Match each vocabulary work with its correct definition.
cofactors
denatured
energy
entropy
enzyme
metabolism
oxidation
reactant
substrate
vitamins
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
Capacity to do work and bring about change; occurs in a variety of forms.
Measure of disorder or randomness.
All of the chemical changes that occur within a cell.
Substance that participates in a reaction.
Organic catalyst, usually a protein, which speeds a reaction in cells due
to its particular shape.
Reactant in a reaction controlled by an enzyme.
Loss of an enzyme's normal shape so that it no longer functions;
caused by a less than optimal pH and temperature.
Nonprotein adjunct required by an enzyme in order to function;
many are metal ions, while others are coenzymes.
Essential requirement in the diet, needed in small amounts. They are
often part of coenzymes.
Loss of one or more electrons from an atom or molecule;
in biological systems, generally the loss of hydrogen atoms
a. ______________________________________
b. ______________________________________
c. ______________________________________
d. ______________________________________
e. ______________________________________
f. ______________________________________
g. ______________________________________
h. ______________________________________
i. ______________________________________
j. ______________________________________
Do not refer to the text when taking this test.
1. The useful energy conversion in
photosynthesis is
a. chemical to solar.
b. heat to mechanical.
c. mechanical to heat.
d. solar to chemical. __
2. Any energy transformation involves the
loss of some energy as
a. electricity,
b. heat.
c. light.
d. motion.
3. In the enzymatically controlled chemical
reaction A  B + C, A is the
a. cofactor.
b. enzyme.
c. product.
d. substrate. __
4. An enzyme, functioning best at a pH of
3, is in a neutral solution at a temperature
of 40°C. Its activity will increase by
a. decreasing the amount of substrate.
b, denaturing the enzyme.
c. increasing the temperature 10 more
degrees.
d, making the pH more acidic. __
5. In the reaction A + B  C, the reaction
rate may slow down through feedback
inhibition by
a. increasing the concentration of A.
b. increasing the concentration of B,
c. increasing the concentration of C.
d. decreasing the concentration of B. __
6. The energy laws
a. account for why energy does not
cycle.
b. say that some loss of energy always
accompanies transformation.
c. say that energy can be made
available to living things.
d. All of these are correct. __
7. In a metabolic pathway
A  B C  D  E,
a. A, B, C, and D are substrates.
b. B, C, D, and E are products.
c. each reaction requires its own
enzyme.
d. All of these are correct.
__
8. The enzyme-substrate complex
a. indicates that an enzyme has
denatured.
b. accounts for why enzymes lower the
energy of activation.
c. is nonspecific.
d. All of these are correct.
9. The tendency for an ordered system to
become spontaneously disordered is
called
a. thermodynamics.
b. entropy.
c. activation
d. energy conversion.
10. A coupled reaction occurs when energy
released from a(n)
reaction is
used to drive a(n)
reaction.
a. endergonic; exergonic
b. breakdown; exergonic
c. exergonic; endergonic
d. chemical; mechanical
11. NAD+ and FAD are
a. dehydrogenases.
b. proteins.
c. coenzymes.
d. Both a and c are correct.
12. Reduction has occurred
a. when electrons are lost.
b. when C6H12O6 becomes CO2.
c. when CO2 becomes H2O.
d. when heat is given off.
e. when ADP becomes ATP.
13. Chloroplasts
a. take in CO2.
b. give off H2O.
c. pass on solar energy,
d. occur in all living things,
e. Both a and c are correct.
14. ATP is used for
a. chemical work.
b. transport work.
c. mechanical work.
d. All of these are correct.
15. NAD and NADP
a. are found only in plants,
b. do not participate in metabolic
reactions.
c. are coenzymes of oxidation-reduction.
d. carry hydrogen atoms.
e. Both c and d are correct.
16. Which statement is NOT correct about
enzymes?
a. They usually end in the suffix "-ase."
b. They catalyze only one reaction.
c. They increase the energy of
activation.
d. They bind temporarily with the
substrate.
19. Since energy does not cycle, animal cells
a. require a continuing source of glucose.
b. are dependent on plant cells.
c. must produce ATP nonstop.
d. All of these are correct.
20. Synthetic reactions
a. require the participation of ATP.
b. do not require enzymes.
c. are represented by S + E  ES  P.
d. are coupled directly to glucose
breakdown.
17. Which of these is NOT expected to
increase the rate of an enzymatic
reaction?
a. add more enzyme
b. remove inhibitions
c. boil rapidly
d. adjust the pH to optimum level
18. Which of these accurately represents a
flow of energy from the sun?
a. Plants take in solar energy and use it to
oxidize glucose, which is used by
mitochondria to produce ATP.
b, Mitochondria break down glucose to
ATP, which is returned to plants to
produce glucose.
c. Plants take in solar energy and use it to
transport water up stems so that water is
available to all animals.
d. Plants take in solar energy and use it to
reduce carbon dioxide so thai glucose is
made available to animals.
e. Both plants and animals make and use
ATP.
Answer in complete sentences.
21. Why couldn't life exist without a continual supply of solar energy?
22. Why are enzymes absolutely necessary to the continued existence of a cell?
ANSWER KEY
l. a. F, chemical energy of ATP can be
transformed into other types of energy such us
kinetic energy (muscle contract ion). b. F, Cells
transform the energy of glucose breakdown into
ATP molecules, and they do obey the first law of
thermodynamics, c. T d. F. Because our
society uses coal as an energy source, it is
increasing the entropy of the universe.
2. a. Ex
b. En c. En d. Ex e.En
3. a. P
b. ATP
c.P
5. a. energy currency b. chemical c. transport
d. mechanical
e. coupled
b. products
7. a. energy of reactant
c. energy of product
e. energy of activation
c. enzymes
b. energy of activation
d. energy of reactant
f. energy of product
8. a. active site b. substrate
d. enzyme-substrate complex
f. products
11. a.increases b. decreases
d. decreases
e. decreases
12. a.coenzymes
c. enzyme
e. enzyme
9. a. enzyme-substrate complex
b. Reactants come together when the enzymesubstrate complex forms.
10. a. E + S  ES  E + P
b. degradative
c. The reactant is broken down.
d. active
e. The enzyme is not broken down and can be used
over and over again.
f. Enzymes are specific to
c. increases
b. help enzymes function.
13. a. loss b. gain
c. loss
e. gain
f. hydrogen
14. a. water
b. oxygen
dioxide
d. glucose
d. ADP
4. a. L. because during cellular respiration, the
chemical energy within a glucose molecule is
converted to the chemical energy within ATP.
b. R, because when muscles contract, the
chemical energy within ATP is converted to the
kinetic energy of muscle contraction.
c. R, because when active transport occurs, the
energy released by ATP breakdown is used to
pump a molecule across the plasma membrane.
6. a. reactants
d. substrate
their substrates.
d. hydrogen
c. carbon
e. sun
15. a. glucose b. carbon dioxide
d. water
e. ATP
16. a. H2O and C02
c. H2O and CO2
c. oxygen
b. O2 and C6 H1206
17. a. solar energy b. glucose c. ATP d. heat
18. a. energy b. entropy c. metabolism
d. reactant e. enzyme f. substrate g. denatured
h. cofactors i. vitamins
j. oxidation
Multiple Choice Questions 1. d 2. b 3. d 4. d
5. c 6. d 7. d 8. b 9. b 10. c 11. d 12. c
13. a 14. d 15. e 16. c 17. c 18. d 19. d
20.a
21. When chloroplasts carry on photosynthesis,
solar energy is converted to the energy of
carbohydrates, and when mitochondria complete
cellular respiration, the energy stored in
carbohydrates is converted to energy temporarily
held by ATP. The energy released by ATP
breakdown is used by the cell to do various types of
work, and eventually it becomes nonusable heat.
22. Enzymes are absolutely essential for the existence of a cell -because they lower the energy of
activation of a reaction, thereby requiring less heat
to bring about the reaction. At high temperatures,
proteins would denature