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Biochemistry > Discussion 4 > Flashcards

Discussion 4 Flashcards

1
Q

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.

A

Water is more likely to act as a hydrogen bond donor than a hydrogen bond acceptor.

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2
Q

According to the Brönsted-Lowry definition, a _______________ is a substance that can accept a proton.

A

Base

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3
Q

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

A

Hydrogens interact with the chloride ion; oxygens interact with the sodium ion.

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4
Q

Which of the following functional groups has two hydrogen bond donors and one hydrogen bond acceptor?

alcohol

ester

thiol

amine

amide

A

Amine

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5
Q

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

A

water molecules are connected to each other by H-bonds

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6
Q

What is the conjugate acid of H2PO4-?

HPO42-

H2PO4

H3PO4

PO43-

none of the above

A

H3PO4

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7
Q

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+

A

H2CO3 ⇆ HCO3- + H+

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8
Q

In an enzyme catalyzed reaction, the reactant that the enzyme interacts with is called the ___________.

coenzyme

cofactor

prosthetic group

substrate

A

substrate

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9
Q

The active site for elastase contains valine. Which amino acid would be most likely to bind to the active site?

Ala

Asp

Ser

Met

A

Ala

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10
Q

Another name for a biological catalyst is a(n) _________________.

inhibitor

enzyme

regulator

subunit

A

enzyme

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11
Q

For a Michaelis-Menten kinetics enzyme Vmax decreases, and KM increases, for which type of inhibition?

competitive

uncompetitive

suicide

mixed

A

mixed

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12
Q

Zinc is required for carbonic anhydrase to properly work. It is an example of a(n) ___________?

cofactor

coenzyme

ion catalyst

suicide inhibitor

A

cofactor

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13
Q

Which of these amino acid groups would not make a good nucleophilic catalyst?

amino
sulfhydryl
imidazole
methyl
hydroxyl

A

methyl

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14
Q

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.

A

general acid catalysis.

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15
Q

Acid-base catalysis may be accomplished by:

active site specificity
charge delocalization
buffer effects
induced strain
conformational change

A

charge delocalization

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16
Q

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.

A

It can trigger cell signaling cascades and be turned on or off.

17
Q

Chymotrypsin catalyzes the hydrolysis of a peptide bond and is therefore categorized as a(n) _____.

oxidoreductase

transferase

hydrolase

lyase

ligase

A

hydrolase

18
Q

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

A

the transition state

19
Q

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.

A

It depends on the energy difference between E + P and the transition state.

20
Q

If A → B is a zero-order reaction, the rate is dependent on the ______________

A

Rate constant

21
Q

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

A

hyperbolic curve; saturated with substrate

22
Q

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

A

enzyme-substrate complex

23
Q

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]

A

v = k2[ES]

24
Q

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

A

d[ES] / dt = 0

25
Q

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

A

KM = (k2 + k-1) / k1

26
Q

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])

A

vo = Vmax [S] / (KM + [S])

27
Q

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

A

the [S] that half-saturates the enzyme

28
Q

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

A

I

29
Q

A Lineweaver-Burk plot is a _____.

double reciprocal plot

Michaelis-Menten plot

sigmoidal plot

hyperbolic plot

logarithmic plot

A

double reciprocal plot

30
Q

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

A

kcat/KM is near the diffusion-controlled limit

31
Q

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

A

small; large

32
Q

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

A

suicide substrates

Biochemistry (32 decks)

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