Discussion 4 Flashcards
Which of the following statements is not accurate when considering water and biological molecules?
Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.
Polar substances are soluble because of their interaction with water.
The hydrogen bonding pattern of water is disrupted by the presence of hydrophobic molecules.
Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.
According to the Brönsted-Lowry definition, a _______________ is a substance that can accept a proton.
Base
Which of the following explains the interactions that occur between the atoms of water molecules and the ions that form when sodium chloride dissolves in water?
Hydrogens interact with the sodium ion; oxygens interact with the chloride ion.
Hydrogens interact with the chloride ion; oxygens interact with the sodium ion.
Hydrogens interact with the sodium ion and the chloride ion.
Oxygens interact with the sodium ion and the chloride ion.
none of the above
Hydrogens interact with the chloride ion; oxygens interact with the sodium ion.
Which of the following functional groups has two hydrogen bond donors and one hydrogen bond acceptor?
alcohol
ester
thiol
amine
amide
Amine
The boiling point of water is 264°C higher than the boiling point of methane because ______.
the molecular mass of methane is much lower than that of water
methane molecules tend to avoid contact with each other
water molecules are connected to each other by H-bonds
methane molecules do not undergo London dispersion forces
all of the above
water molecules are connected to each other by H-bonds
What is the conjugate acid of H2PO4-?
HPO42-
H2PO4
H3PO4
PO43-
none of the above
H3PO4
Which of the following shows the buffer that is found in the bloodstream?
H3PO4 ⇆ H2PO42- + H+
H2PO4- ⇆ HPO42- + H+
HPO42- ⇆ PO43- + H+
H2CO3 ⇆ HCO3- + H+
HCO3- ⇆ CO32- + H+
H2CO3 ⇆ HCO3- + H+
In an enzyme catalyzed reaction, the reactant that the enzyme interacts with is called the ___________.
coenzyme
cofactor
prosthetic group
substrate
substrate
The active site for elastase contains valine. Which amino acid would be most likely to bind to the active site?
Ala
Asp
Ser
Met
Ala
Another name for a biological catalyst is a(n) _________________.
inhibitor
enzyme
regulator
subunit
enzyme
For a Michaelis-Menten kinetics enzyme Vmax decreases, and KM increases, for which type of inhibition?
competitive
uncompetitive
suicide
mixed
mixed
Zinc is required for carbonic anhydrase to properly work. It is an example of a(n) ___________?
cofactor
coenzyme
ion catalyst
suicide inhibitor
cofactor
Which of these amino acid groups would not make a good nucleophilic catalyst?
amino
sulfhydryl
imidazole
methyl
hydroxyl
methyl
Proton transfer from an acid, lowering the free energy of a reaction’s transition state, is characteristic of
electrostatic catalysis.
nucleophilic catalysis.
general base catalysis.
general acid catalysis.
concerted acid-base catalysis.
general acid catalysis.
Acid-base catalysis may be accomplished by:
active site specificity
charge delocalization
buffer effects
induced strain
conformational change
charge delocalization
Which statement about phosphorylation is TRUE?
It is an irreversible covalent modification.
It is carried out by phosphatases.
It can alter the charges on proteins by making them more positively charged.
It can trigger cell signaling cascades and be turned on or off.
It can trigger cell signaling cascades and be turned on or off.
Chymotrypsin catalyzes the hydrolysis of a peptide bond and is therefore categorized as a(n) _____.
oxidoreductase
transferase
hydrolase
lyase
ligase
hydrolase
The highest point in a reaction coordinate diagram represents _____.
an intermediate of the reaction pathway
the reactants in an exergonic reaction
the products in an endergonic reaction
the transition state
the overall ∆G for the reaction
the transition state
If you add enzymes to a solution containing only the product(s) of a reaction, would you expect any substrate to form?
It depends on the time interval and temperature of reaction.
It depends on the concentration of products added.
It depends on the energy difference between E + P and the transition state.
All of the above may determine if product forms.
None of the above determines if product forms.
It depends on the energy difference between E + P and the transition state.
If A → B is a zero-order reaction, the rate is dependent on the ______________
Rate constant
A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _____. This indicates that at some point, the enzyme is _____.
straight line; inhibited by product
hyperbolic curve; saturated with substrate
sigmoidal curve; inhibited by substrate
hyperbolic curve; activated by substrate
sigmoidal curve; saturated with substrate
hyperbolic curve; saturated with substrate
When a substrate and enzyme interact, the first chemical species formed is the _____.
enzyme-substrate complex
enzyme-transition state complex
enzyme-product complex
enzyme plus product
none of the above
enzyme-substrate complex
Which of the following expresses the velocity for an enzyme-catalyzed reaction that obeys Michaelis-Menten kinetics?
v = k1[E][S]
v = k1[E][S] – k-1[ES]
v = k1[E][S] + k2[ES]
v = k2[ES]
v = k2[ES] – k-1[ES]
v = k2[ES]
Which of the following must be true if the steady state assumption is to be used?
[E]T = [ES]
(k2 – k-1) / k1 = 1
k1[E][S] = k2[ES]
k1[E][S] = k2[ES] – k-1[ES]
d[ES] / dt = 0
d[ES] / dt = 0
The Michaelis constant is defined as _____.
KM = k2 / k1
KM = (k2 + k-1) / k1
KM = (k2 – k-1) / k1
KM = (k2 + k1) / k-1
KM = (k2 – k1) / k-1
KM = (k2 + k-1) / k1
Which of the following properly expresses the Michaelis-Menten equation?
vo = Vmax [S] / (KM + [S])
vo = Vmax KM / (KM + [S])
kcat = Vmax / [E]T
Vmax = vo [S] / (KM + [S])
Vmax = vo KM / (KM + [S])
vo = Vmax [S] / (KM + [S])
KM is _____.
a measure of the catalytic efficiency of the enzyme
equal to half of Vmax
the rate constant for the reaction ES ⇆ E + P
the [S] that half-saturates the enzyme
a ratio of substrate concentration relative to catalytic power
the [S] that half-saturates the enzyme
The Michaelis constant KM is defined as _____.
I. (k–1 + k2)/k1
II. one-half Vmax
III. [S] = [ES]
IV. [ES]/2
I
I, II
II
I, IV
II, IV
I
A Lineweaver-Burk plot is a _____.
double reciprocal plot
Michaelis-Menten plot
sigmoidal plot
hyperbolic plot
logarithmic plot
double reciprocal plot
Which of the following indicates that an enzyme has evolved to its most efficient form?
kcat is a large number
KM is a small number
KM is a large number
kcat/KM is a small number
kcat/KM is near the diffusion-controlled limit
kcat/KM is near the diffusion-controlled limit
An extremely efficient enzyme has a _____ KM and a _____ kcat.
small; small
small; large
large; large
large; small
kcat and KM do nothing to predict the efficiency of an enzyme
small; large
Some irreversible inhibitors are called _____ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate.
irreversible substrates
suicide substrates
noncompetitive substrates
ping pong substrates
allosteric substrates
suicide substrates
