Chapter 8: Enzymes and Metabolism
Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible?
ATP can be regenerated by the addition of a phosphate group to ADP
Which of the following statements describes a central role that ATP plays in cellular metabolism?
ATP provides energy coupling between exergonic and endergonic reactions
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of _____.
a catabolic pathway
Chemical equilibrium is relatively rare in living cells because metabolic pathways are interconnected. What is an example of a reaction that may be at chemical equilibrium in a cell?
a chemical reaction in which neither the reactants nor the products are being produced or consumed in any metabolic pathway at that time in the cell
What are metabolic pathways?
a series of reactions, each catalyzed by a different enzyme
Competitive inhibitors bind to the __________ of an enzyme, while noncompetitive inhibitors bind to an enzyme's __________.
active site, allosteric site
The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of __________.
allosteric regulation
What is an important consequence of the first law of thermodynamics for a living organism?
an organism ultimately must obtain all of the necessary energy for life from its environment
How does ATP drive mechanical work inside a cell?
by binding to motor proteins
How does ATP drive transport work inside a cell?
by phosphorylating a transport protein
If a system is in equilibrium, it cannot __________.
do work
What is a logical consequence of the second law of thermodynamics?
each chemical reaction in an organism must increase the total entropy of the universe
A chemical reaction that has a positive ΔG is best described as _____.
endergonic
Is this reaction endergonic or exergonic? glucose + fructose → sucrose
endergonic
Which of the following states the relevance of the first law of thermodynamics to biology?
energy can be freely transformed among different forms as long as the total energy is conserved
If the entropy of a living organism is decreasing, what is most likely to be occurring simultaneously?
energy input into the organism must be occurring to drive the decrease in entropy
The primary manner in which cells manage their energy resources in order to do work is called energy coupling. Which statement accurately defines energy coupling?
exergonic reactions drive endergonic reactions
ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.
feedback inhibition
Why is enzyme activity affected by pH?
high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site
What type of reaction breaks the bonds that join the phosphate groups in an ATP molecule?
hydrolysis
Why do hydrolysis reactions occur more readily in solution than dehydration reactions?
hydrolysis reactions are exergonic and increase entropy of the system
Do enzymes change the ΔG of a reaction?
no
Cofactors:
nonprotein enzyme helpers, mostly metal ions
Coenzymes:
nonprotein enzyme helpers, organic molecules that are a specific kind of cofactor
What would the value of ΔS be for a chemical reaction in which a molecule is broken down into smaller components?
positive
An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy.
releases, absorbs
In general, the hydrolysis of ATP drives cellular work by __________.
releasing free energy that can be coupled to other reactions
The action of inhibitors may be __________.
reversible or irreversible
Why can't most cells harness heat to perform work?
temperature is usually uniform throughout a cell
What is changed by the presence of an enzyme in a reaction?
the activation energy (Ea)
What is an example of the second law of thermodynamics as it applies to biological reactions?
the aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water
Why do bonds form potential energy?
the energy arises from the relative positions of the atoms that form the bond
What is true about the entropy of the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O)?
the entropy of the products is greater than the entropy of the reactants
At low pH, a particular enzyme catalyzes a reaction at a high rate. At neutral pH, the enzyme is completely inactive. What statement best explains the difference in how pH affects the function of this enzyme?
the enzyme is adapted for a low pH but is denatured at neutral pH, leaving it nonfunctional
What best characterizes the role of ATP in cellular metabolism?
the free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate
What is true for all exergonic reactions?
the reaction proceeds with a net release of free energy
Why can't enzymes change the equilibrium point?
they cannot change the net energy output
How is the energy of ATP released?
through the hydrolysis of one of the phosphate groups
