BIOC 3021 Exam 2 Questions and
Answers 100% Solved | Graded A+
In addition to the basic ES intermediate in an enzyme reaction, what other
types of intermediates are formed and why are these intermediates so
important? - ✔✔Transition states occur in enzyme reactions that are
important in product stabilization and changes in energy.
Why would researchers try to determine the initial rate of enzyme activity
(V0) at a very early time point in the reaction? What happens later in the
reaction? Why does this happen? - ✔✔The initial velocity should be
determined early in the reaction because the velocity will change later due
to changes in substrate concentration.
Why does a plot of V vs S taper off and eventually reach a plateau at
higher S levels? - ✔✔Substrate has filled all enzyme active sites and
adding more will not increase the rate of reaction.
What is the Michaelis-Menten Equation? The M-M Equation uses the terms
(V), ( Vmax), (S) and (Km). What do each of these terms mean? - ✔✔The
velocity of the reaction equals maximum velocity times substrate
1
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,concentration divided by the sum of the substrate concentration and the
Michaelis constant, which has units of concentration.
Why can the rate constant K-2 be ignored in the derivation of the M-M
Equation? - ✔✔There is little product formed early in the reaction, so the
reverse reaction can be ignored.
Why is a V vs S plot linear at low S concentrations? Why does the plot
curve off at intermediate S levels, and why does it plateau at high S levels?
- ✔✔The V vs S plot is linear at low S concentrations because the M-M
equation reduces to V = Vmax * [S] / Km, which is a linear equation. The
plot then curves at intermediate levels with increasing substrate
concentration, and plateaus at high S levels due to the M-M equation
approaching Vmax.
What does the Km term tell us about an enzyme? What does it signify if an
enzyme has a low Km or a high Km? What is the enzyme rate when the
concentration of S = Km? - ✔✔Km tells us about an enzyme's efficiency; a
low Km indicates an efficient enzyme, while a high Km indicates a less
efficient enzyme. When the Km and substrate concentration are equal, the
velocity of the reaction is equal to half the maximum possible velocity of the
reaction.
2
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What is the definition of turnover number and how does that constant relate
to the Vmax of an enzyme? What is the absolute value of the turnover
number for the enzyme catalase and what does that mean in terms of the
amount of substrate used by a single molecule of the enzyme per second?
Why doesn't the turnover number of an enzyme change as the enzyme is
purified? - ✔✔The turnover number is the number of molecules of substrate
that can be converted per second per molecule of enzyme. It is equal to
Vmax divided by the concentration of the enzyme. The enzyme catalase
the absolute value of the turnover number is forty million, so it can still
function efficiently even with a poor Km. Turnover number doesn't change
as the enzyme is purified because it's an intrinsic property of enzymes.
What is the Lineweaver-Burk equation? How does it relate to the M-M
Equation and how is it used to determine the Km and Vmax of an enzyme?
- ✔✔1/v = 1/vmax + Km/(vmax*[S]). It is essentially the M-M equation
flipped. -1/Km = 1/[S] intercept, 1/vmax = 1/v intercept.
What is the difference between a reversible and an irreversible inhibitor?
What is the mode of action for the two most common reversible inhibitors,
competitive and noncompetitive? When examined using a Lineweaver-Burk
plot, how do each of these inhibitors change the plots? What information
can be gained by examination of the intersection of these plots with the X
3
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
, and Y intercepts? - ✔✔Reversible inhibitors cause covalently-modified
changes to enzymes that cannot be undone, while reversible inhibitors do
not. Competitive inhibitors reversibly bind at an enzyme's active site. This
increases the Km and thus shifts the LB plot to the right. Noncompetitive
inhibitors reversibly bind at a non-active site of an enzyme and exert their
effects allosterically. This decreases the Vmax of the reaction and shifts the
LB plot up the y-axis (1/v axis).
What is the mode of action of irreversible inhibitors? Why are they
irreversible? What is the specificity of action of TPCK, DIFP, and
iodoacetamide? How can these inhibitors help determine the character of
an enzyme's active site? - ✔✔Irreversible inhibitors cause covalently-
modified changes to enzymes, usually in the active sites. TPCK binds at
the active site of chymotrypsin with a histidine residue. DIFP reacts with
active sites of serine proteases like chymotrypsin and modifies the active
site serine residue of acetylcholinesterase. Iodoacetamide reacts with the
active site of cysteine proteases by covalently bonding with the sulfur atom.
These inhibitors can help determine the character of an enzyme's active
site, since they will only inhibit if certain residues exist.
What are the common mechanisms used by enzymes to achieve catalysis?
How do these mechanisms reduce or increase the energy level of an
4
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
Answers 100% Solved | Graded A+
In addition to the basic ES intermediate in an enzyme reaction, what other
types of intermediates are formed and why are these intermediates so
important? - ✔✔Transition states occur in enzyme reactions that are
important in product stabilization and changes in energy.
Why would researchers try to determine the initial rate of enzyme activity
(V0) at a very early time point in the reaction? What happens later in the
reaction? Why does this happen? - ✔✔The initial velocity should be
determined early in the reaction because the velocity will change later due
to changes in substrate concentration.
Why does a plot of V vs S taper off and eventually reach a plateau at
higher S levels? - ✔✔Substrate has filled all enzyme active sites and
adding more will not increase the rate of reaction.
What is the Michaelis-Menten Equation? The M-M Equation uses the terms
(V), ( Vmax), (S) and (Km). What do each of these terms mean? - ✔✔The
velocity of the reaction equals maximum velocity times substrate
1
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,concentration divided by the sum of the substrate concentration and the
Michaelis constant, which has units of concentration.
Why can the rate constant K-2 be ignored in the derivation of the M-M
Equation? - ✔✔There is little product formed early in the reaction, so the
reverse reaction can be ignored.
Why is a V vs S plot linear at low S concentrations? Why does the plot
curve off at intermediate S levels, and why does it plateau at high S levels?
- ✔✔The V vs S plot is linear at low S concentrations because the M-M
equation reduces to V = Vmax * [S] / Km, which is a linear equation. The
plot then curves at intermediate levels with increasing substrate
concentration, and plateaus at high S levels due to the M-M equation
approaching Vmax.
What does the Km term tell us about an enzyme? What does it signify if an
enzyme has a low Km or a high Km? What is the enzyme rate when the
concentration of S = Km? - ✔✔Km tells us about an enzyme's efficiency; a
low Km indicates an efficient enzyme, while a high Km indicates a less
efficient enzyme. When the Km and substrate concentration are equal, the
velocity of the reaction is equal to half the maximum possible velocity of the
reaction.
2
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
,What is the definition of turnover number and how does that constant relate
to the Vmax of an enzyme? What is the absolute value of the turnover
number for the enzyme catalase and what does that mean in terms of the
amount of substrate used by a single molecule of the enzyme per second?
Why doesn't the turnover number of an enzyme change as the enzyme is
purified? - ✔✔The turnover number is the number of molecules of substrate
that can be converted per second per molecule of enzyme. It is equal to
Vmax divided by the concentration of the enzyme. The enzyme catalase
the absolute value of the turnover number is forty million, so it can still
function efficiently even with a poor Km. Turnover number doesn't change
as the enzyme is purified because it's an intrinsic property of enzymes.
What is the Lineweaver-Burk equation? How does it relate to the M-M
Equation and how is it used to determine the Km and Vmax of an enzyme?
- ✔✔1/v = 1/vmax + Km/(vmax*[S]). It is essentially the M-M equation
flipped. -1/Km = 1/[S] intercept, 1/vmax = 1/v intercept.
What is the difference between a reversible and an irreversible inhibitor?
What is the mode of action for the two most common reversible inhibitors,
competitive and noncompetitive? When examined using a Lineweaver-Burk
plot, how do each of these inhibitors change the plots? What information
can be gained by examination of the intersection of these plots with the X
3
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
, and Y intercepts? - ✔✔Reversible inhibitors cause covalently-modified
changes to enzymes that cannot be undone, while reversible inhibitors do
not. Competitive inhibitors reversibly bind at an enzyme's active site. This
increases the Km and thus shifts the LB plot to the right. Noncompetitive
inhibitors reversibly bind at a non-active site of an enzyme and exert their
effects allosterically. This decreases the Vmax of the reaction and shifts the
LB plot up the y-axis (1/v axis).
What is the mode of action of irreversible inhibitors? Why are they
irreversible? What is the specificity of action of TPCK, DIFP, and
iodoacetamide? How can these inhibitors help determine the character of
an enzyme's active site? - ✔✔Irreversible inhibitors cause covalently-
modified changes to enzymes, usually in the active sites. TPCK binds at
the active site of chymotrypsin with a histidine residue. DIFP reacts with
active sites of serine proteases like chymotrypsin and modifies the active
site serine residue of acetylcholinesterase. Iodoacetamide reacts with the
active site of cysteine proteases by covalently bonding with the sulfur atom.
These inhibitors can help determine the character of an enzyme's active
site, since they will only inhibit if certain residues exist.
What are the common mechanisms used by enzymes to achieve catalysis?
How do these mechanisms reduce or increase the energy level of an
4
©JOSHCLAY 2024/2025. YEAR PUBLISHED 2024.
