Chapter 8: Energy
Which of the following statements is consistent with the second law of thermodynamics?
A constant input of energy is required to maintain the high level of organization associated with living cells.
entropy
A measure of disorder or randomness.
feedback inhibition
A method of metabolic control in which the end product of a metabolic pathway acts as an inhibitor of an enzyme within that pathway.
phosphorylated intermediate
A molecule (often a reactant) with a phosphate group covalently bound to it, making it more reactive (less stable) than the unphosphorylated molecule.
catalysis
A process by which a chemical agent called a catalyst selectively increases the rate of a reaction without being consumed by the reaction.
metabolic pathway
A series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds.
noncompetitive inhibitor
A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing its conformation so that it no longer binds to the substrate.
ATP+H2O→
ADP+℗i
coenzyme
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.
Which of the following correctly states the relationship between anabolic and catabolic pathways?
Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways
How do enzymes lower activation energy?
By locally concentrating the reactants
induced fit
Caused by entry of the substrate, the change in shape of the active site of an enzyme so that it binds more snugly to the substrate.
Which of the following statements best summarizes an important consequence of the first law of thermodynamics for living organisms?
Each organism ultimately must obtain all of the necessary energy for life from its environment.
first law of thermodynamics
Energy can be transferred and transformed, but it cannot be created or destroyed.
chemical energy
Energy stored in chemical bonds
second law of thermodynamics
Every energy transfer or transformation increases the entropy of the universe.
Which of the following statements best describes a relationship between the evolution of multicellular life on Earth and the laws of thermodynamics?
Evolution has occurred in accordance with the laws of thermodynamics and resulted in an increase in the entropy of the universe.
Which of the following statements best summarizes a consequence of the second law of thermodynamics?
If entropy of a system decreases, there must be a corresponding increase in the entropy of the universe.
When 1 mole of ATP is hydrolyzed in a test tube without an enzyme, about twice as much heat is given off as when 1 mole of ATP is hydrolyzed in a cell. Which of the following best explains these observations?
In the cell, the hydrolysis of ATP is coupled to other endergonic reactions.
anabolic pathways
Metabolic pathways that consume energy to build complicated molecules from simpler ones.
catabolic pathways
Metabolic pathways that release energy by breaking down complex molecules into simpler compounds.
What do the sign and magnitude of the ΔG of a reaction tell us about the speed of the reaction?
Neither the sign nor the magnitude of ΔG has anything to do with the speed of a reaction
cofactor
Non-protein helpers that may be bound tightly to the enzyme as a permanent resident, or may bind loosely and reversibly along with the substrate.
Organisms are described as thermodynamically open systems. Which of the following statements is consistent with this description?
Organisms acquire energy from and lose energy to their surroundings.
What is an example of the cellular work involved in the production of electrochemical gradients?
Proton movement against a gradient of protons
The binding of an allosteric inhibitor to an enzyme causes the rate of product formation by the enzyme to decrease. Which of the following best explains why this decrease occurs?
The allosteric inhibitor causes a structural change in the enzyme that prevents the substrate from binding at the active site.
allosteric regulation
The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.
Metabolic pathways in cells are typically far from equilibrium. Which of the following processes tend(s) to keep these pathways away from equilibrium?
The continuous removal of the products of a pathway to be used in other reactions An input of free energy from outside the pathway
What is meant by the "induced fit" of an enzyme?
The enzyme changes its shape slightly as the substrate binds to it.
active site
The part of an enzyme or antibody where the chemical reaction occurs.
Molecules A and B contain 110 kcal/mol of free energy, and molecules B and C contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded?
The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants.
thermal energy
The total energy of motion in the particles of a substance heat energy
What is true of allosteric proteins?
They are acted on by inhibitors. They are sensitive to environmental conditions. They exist in active and inactive conformations.
Which of the following is a characteristic feature of anabolic pathways?
They consume energy to build up polymers from monomers
Consider the growth of a farmer's crop over a season. Which of the following correctly states a limitation imposed by the first or second law of thermodynamics?
To obey the first law, the crops must represent an open system.
any change from the equilibrium state will be
a positive ΔG and will not be spontaneous
enzyme-substrate complex
a temporary complex formed when an enzyme binds to its substrate molecules
ΔG has a negative value for
all spontaneous processes
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule outside the active site is an example of __________.
allosteric activation
Open systems are those in which energy and materials
can be exchanged between the system and its surroundings.
Energy released from downhill catabolic rxns
can be stored and then used to drive uphill reaction of anabolic pathways
mechanical work
cell motility and movement of structures within cells
Enzymes can lower the activation energy of reactions, but they cannot
change the equilibrium point because they cannot change the net energy output.
there are 10 million molecules of ATP
consumed and regenerated per cell per second
endergonic reaction
energy inward a spontaneous chemical reaction in which there is a net absorption of energy from the surroundings -ΔG
kinetic energy
energy of motion
Exergonic reaction
energy outward a spontaneous chemical reaction in which there is a net release of free energy +ΔG
living systems increase the
entropy of their surroundings
hydrolyzing atp is a
enzymatic activity
the free energy required to phosphorylate ATP comes from the
exergonic breakdown reactions or catabolisms in the cell
the key to coupling exergonic and endergonic rxns is the
formation of a phosphorylated intermediate
Catabolic reactions (catabolism)
harvest energy by breaking down molecules
Enzyme activity is affected by pH because __________.
high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
energy coupling
in cellular metabolism the use of energy released from an exergonic reaction to drive an endergonic reaction
The coupling of ATP to other endergonic processes in cells means that
less of the free energy is released as heat. When ATP is hydrolyzed without this coupling, all of the energy is released as heat.
for the reaction to have a negative ΔG the system must
lose free energy and ΔG has to be negative
If a reaction is exergonic, the formation of
new bonds releases more energy than was invested in breaking the old bonds.
Competitive inhibition of enzymes
occurs when a substance other than the substrate binds to the active site of an enzyme
substrate
reactant of an enzyme-catalyzed reaction
An exergonic (spontaneous) reaction is a chemical reaction that __________.
releases energy when proceeding in the forward direction
The action of competitive inhibitors may be
reversible or irreversible.
potential energy
stored energy that results from the position or shape of an object
an endergonic reaction essentially
stores free energy in molecules
the free-energy change of a reaction
tells us whether or not the reaction occurs spontaneously
ΔG
the change in free energy the difference between the free energy of the final state and the final energy of the initial state
ΔH
the change in the systems enthalpy/total energy
ΔS
the change in the systems entropy
Much of the suitability of ATP as an energy intermediary is related to the instability of the bonds between the phosphate groups. These bonds are unstable because __________.
the negatively charged phosphate groups vigorously repel one another and the terminal phosphate group is more stable in water than it is in ATP
A chemical reaction is designated as exergonic rather than endergonic when __________.
the potential energy of the products is less than the potential energy of the reactants
transport work
the pumping of substances across membranes against the direction of spontaneous movement
Chemical work
the pushing of endergonic reactions that would not occur spontaneously
thermodynamics
the study of the energy transformations that occur in a collection of matter
Enzymes speed up the rate of the reaction .
without changing the DeltaG for the reaction
Which part of the equation ΔG = ΔH - TΔS tells you if a process is spontaneous?
ΔG
what is the ΔG of the ATP hydrolysis rxn?
ΔG=−7.3 kcal/mol (−30.5 kJ/mol)
for ΔG to be negative
ΔH must be negative or TΔS must be positive
If, during a process, the system becomes more ordered, then __________.
ΔS is negative
When one molecule is broken down into six component molecules, which of the following will always be true?
ΔS is positive.
