biochem concepts.docx
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Which of the following statements is true for enzymatically catalyzed reaction?
The activation energy of the reaction is lowered so that a larger proportion of the substrate qualifies to overcome it
Which of the following common drugs is not a specific enzyme inhibitor?
Iodine
Non-competitive inhibitor of an enzyme catalyzed reaction
decreases Vmax binds to Michaelis complex (ES)
The steady state assumption, as applied to enzyme kinetics, implies:
The ES complex is formed and broken down at equivalent rates
The plot commonly used for determining the value of Vmax is
Lineweaver Burk plot Langmuir plot Eadie Hofstee plot
Which of these enzymes contains a Zinc (Zn) ion?
Carboxypeptidase A
A noncompetitive inhibitor of an enzyme-catalyzed reaction
increases KM and reduces Vmax
Vmax for an enzyme-catalyzed reaction:
is twice the rate observed when the concentration of substrate is equal to the Km
The catalytic power of an enzyme is:
a measure of the ability of an enzyme to increase the rate of a reaction
complete DNA sequence of an organism is called
genome
If the Standard Gibb's free energy, ΔG°, for a reaction is positive then
the reactants will be favored
The ratio of the amount of a protein present in a sample, which is used as a measure of purification, is known as
specific activity
If a reaction occurs in the absence of inhibitor with rate ν0 and in the presence of inhibitor with rate νi, the degree of inhibition is defined as
(ν0 - νi)/ν0
Classical noncompetitive inhibition is obtained only under
rapid equilibrium conditions
Enzymes are basically
proteins
Which of the following refers to pseudo steady state ?
d[ES]/dt = 0
A competitive inhibitor of an enzyme is usually
structurally similar to the substrate.
Linear inhibition is sometimes called as
complete inhibition
The conformational change in an enzyme after the substrate is bound that allows the chemical reaction to proceed, can be explained by
induced fit
The enzyme inhibition can occur by
reversible inhibitors irreversible inhibitors
In a Lineweaver-Burk Plot, competitive inhibitor shows which of the following effect?
It changes the x-intercept
The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V0=Km/(Vmax[S]) + 1/Vmax. To determine Km from a double-reciprocal plot, you would:
multiply the reciprocal of the x-axis intercept by −1.
An enzyme and a reactant molecule maintain relationship as
a temporary association
Which of the following activity is possible by transferases?
Transfer of methyl groups Transfer of glycosyl group
Which of the following is the best evidence for the lock and key theory of enzyme action?
Compounds similar in structure to the substrate inhibit enzyme activity
The affinity of an enzyme for its substrate, when the enzyme has a Km of 0.50 M will be __________ than the affinity of an enzyme for its substrate when the enzyme has a Km of 0.05 M.
Lesser
Isozymes or iso enzymes are those enzyme which
have different structural forms but identical catalytic properties
The inactive protein from of enzyme is
Apoenzyme
Total activity / total protein
Specific activity
are antibodies that express a catalytic activity.
Abzymes
The active form of enzyme is
Holoenzyme
The Standard Gibb's free energy, ΔG°, is
the energy required to convert one mole of reactants to one mole of products
The rate equation in competitive inhibition based on Michaelis Menten equation is given by
rmaxS/(Km (1+I/Ki)+S))
In the steady state the material balance equation for any component of a system is
rate of addition - rate of removal + rate of formation = 0
For an enzyme that displays Michaelis-Menten kinetics, the reaction velocity (as a fraction of Vmax) observed at [S] = 2 KM will be
0.66
Predominantly uncompetitive inhibition may be called when
competitive inhibition is greater than uncompetitive inhibition
Most enzymes work by
decreasing energy of activation
When an enzyme is functioning at Vmax, the rate of the reaction is limited by
the rate at which the enzyme can convert substrate to product
Which of the following statements is true?
A reaction may not occur at a detectable rate even though it has a favourable equilibrium At the end of an enzyme-catalyzed reaction, the functional enzyme becomes available to catalyze
the reaction again Substrate binds to an enzyme’s active site Lowering the temperature of a reaction will lower the reaction rate
Which of the following statements is false?
For S → P, a catalyst shifts the reaction equilibrium to the right
The effect of non-competitive inhibition on a Lineweaver-Burk Plot is that
it can move the entire curve to the right it can change the y-intercept it can change the x-intercept
Which of the following statements is true?
Enzymes are proteins that bind to specific substrates and increase the velocity of reactions involving those substrates
Enzymes function by overcoming the activation energy barrier of a reaction Enzymes make thermodynamically favorable reactions to proceed; they cannot make unfavorable
reactions to occur
An enzyme is assayed at an initial substrate concentration of 2 x 10-5M. In 6 minute, half of the substrate is used. The Km for the substrate is 2 x 10-3M. The value of k in minute is
0.115
An allosteric inhibitor of an enzyme usually
participates in feedback regulation
A classical uncompetitive inhibitor is a compound that binds
reversibly to the enzyme substrate complex yielding an inactive ESI complex
Which graphical method is used to determine an enzyme degree of cooperativity?
Hill plot
A substrate binds to its enzyme at a location called the ____ site.
Active
Hydrogen and oxygen release enormous amounts of energy when they react. Yet, hydrogen and oxygen can be mixed together in a balloon and nothing will happen. Why?
Competitive inhibitors are blocking the reaction from occurring in the active site
Functional representation of a genome is called
proteome
Main function of an enzyme is to
decrease the activation energy
For enzymes, an assay usually measures
enzyme activity
____ is the the ability of an enzyme to promote a particular chemical rxn.
enzyme activity
The inactive organic molecular portion of enzyme is
coenzyme
Organic molecules that increase the rate of metabolic reactions with themselves changing are known as
Enzymes
An abzyme (from antibody and enzyme), also called catmab (from _____)
catalytic monoclonal antibody
Enzymes can
not pass through semipermeable membrane
An enzyme has a Km of 4.7 x 10-5M. If the Vmax of the preparation is 22m moles liter-1 min-1, what velocity would be observed in the presence of 2.0 x 10-4M substrate and 5.0 x 10-5M of a competitive inhibitor?
13.54μ moles liter-1min-1
The initial velocity, V0, of an enzyme catalyzed reaction reaches Vmax as
1/[S] → 0
The usual method(s) to solve rate equation of simple enzyme kinetics is/are
Michaelis Menten approach Numerical solution approach
When substrate [S] = KM (Michaelis-Menten constant), the velocity of an enzyme catalyzed reaction is about
0.5 * Vmax
A classical noncompetitive inhibitor has
no effect on substrate binding and vice versa
The active site of an enzyme differs from an antibody-antigen binding site in that the enzyme active site
catalyzes a chemical reaction
Without the presence of enzymes, the reactions necessary to sustain life would require ___________________ in order to occur.
higher temperatures
Which category of enzymes belongs to class 5 in the international classification?
Isomerases
Lock and key theory is based on the compatibility of
enzyme and substrate
When [S] = 0.1 *KM, the velocity of an enzyme catalyzed reaction is about:
0.09 * Vmax
The types of inhibition pattern based on Michaelis Menten equation are
competitive non-competitive uncompetitive
Which of these proteases is not a cysteine active site protease?
Cathepsin D
Given an enzyme with a Km = 10m M and Vmax = 100 m mol/min. If [S] = 100 m M, which of the following will be true?
A 10 fold increase in Vmax would increase velocity 10 fold y
Which category of enzymes belongs to class two in the international classification?
Transferases
The Woolf-Augusteinsson-Hofstee plot of ν versus ν/[S] and the Eadie-Scatchard plot of ν/[S] versus ν do not involve reciprocals of ν therefore are considered to be more reliable when the error in v is
Significant
The relationship between Keq, Km and Vmax is known as
Haldane equation
The reciprocal equation for non competitive inhibition can be arranged to the equation for the
Dixon plot
The concept of "induced fit" refers to the fact that:
substrate binding may induce a conformational change in the enzyme, which thenbrings catalytic groups into proper orientation.
The benefit of measuring the initial rate of a reaction, V0, is that at the beginning of a reaction:
changes in [S] are negligible, so [S] can be treated as a constant.
Which of the following statements about a plot of V0 vs. [S] for an enzyme that follows Michaelis-Menten kinetics is true?
The shape of the curve is a hyperbola. The y-axis is a rate term with units of μΜ/min. As [S] increases, the initial velocity of reaction, V0, also increases. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km
.
To calculate the turnover number of an enzyme you need to know the:
initial velocity of the catalyzed reaction at [S] >> Km. [E]
Quasi steady state is also known as
Briggs-Haldane approach
The active site of an enzyme does not remain
at the center of globular protein rigid and does not change shape complementary to the rest of the molecule
In competitive inhibition a factor is obtained from the measurement of
Km
The rate-determining step of Michaelis Menten kinetics is
the complex dissociation step to produce product
In enzymology, ______ (also termed kcat) is defined as the maximum number of molecules of substrate that an enzyme can convert to product per catalytic site per unit of time
turnover number
The equation for the rate of product formation for simple enzyme reaction is given by (Where rmax, maximum reaction rate, Cs substrate concentration, Cp product concentration ES, CES enzyme-substrate concentration)
rp = rmax Cs/(Km+Cs)
Which of the following step is assumed to be the slowest step in the Michaelis Menten equation?
The product releasing step
Michaelis Menten equation can also be written as
r = rmax-(Km.r/Cs) 1/r = (1/rmax)+(Km/(rmax.Cs)) (-Cs)/r = (Cs/rmax)+(Km/rmax)
The slope of Lineweaver Burk plot for Michaelis Menten equation is
Km/Vmax
The rate equation in non-competitive inhibition based on Michaelis Menten equation is given by
rmaxS/(Km + S)(1+I/Ki)
antibody + enzyme =
abzyme
Enzymes are
organic compounds produced by living organism
Denaturation of an enzyme refers to the
improper arrangement of the enzyme in a metabolic pathway
An exergonic reaction is one that
releases energy for work
If the Keq for an enzymatic reaction is greater than 1, the reaction
will not be endergonic can occur without the input of energy
An endergonic reaction is one that
requires energy in order to proceed
The ability of a competitive inhibitor to bind to an active site in an allosterically controlled enzyme is __________ than the ability of a non-competitive inhibitor to bind to an active site in the same allosterically controlled enzyme.
Greater
In competitive inhibition, an inhibitor:
binds reversibly at the active site.
Enzyme inhibitors are molecules that interact in some way with the enzyme to prevent it from working in the normal manner
competitive inhibitor is any compound which closely resembles the chemical structure and molecular geometry of the substrate.
noncompetitive inhibitor is a substance that interacts with the enyzme, but usually not at the active site
Irreversible Inhibitors are compounds that form strong covalent bonds with an enzyme.
Excess of either acid or base causes denaturing of protein. What type of bonds are disrupted by this action? Salt bridges
Excess of either acid or base causes denaturing of protein. What type of bonds are disrupted by this action? True
The inhibitor may affect those parts of the active site that perform the work of catalysis, resulting in a loss of enzyme activity. True
Most enzymes function within a narrow range of pH. Many have a closely defined optimum pH. Enzymes that function in the stomach usually have lower pH optima than those which are found in the intestine. Enzymes could be expected to be sensitive to minor pH changes because: At very high pH, enzymes are destroyed
What kind of inhibitors attach to the allosteric sites of certain enzymes? Noncompetitive inhibitors
As a solution containing an enzymatic reaction is heated, the temperature rises and the reaction velocity rises gradually for some period but typically falls off very rapidly after reaching the optimum temperature because: The enzyme functions more rapidly as the solution is heated because the molecules move faster, but after a certain temperature, the enzyme becomes denatured
A molecule of an enzyme that has a high turnover number: Converts substrate to product very rapidly
Most synthetic reactions in which carbon dioxide is used require the vitamin biotin. The biotin becomes covalently bound to a lysine molecule that is part of an enzyme, and the biotin can then attach to and carry the carbon dioxide molecule. Biotin is best referred to as an: Coenzyme
A competitive inhibitor of an enzyme-catalyzed reaction always interferes with product release. False
An allosteric enzyme may show a sigmoid dependence on substrate concentration. True
Noncompetitive inhibitors have the ability to change the shape of the active site in such a way that it loses affinity for its substrate. True
Parkinson"s disease is caused by a deficiency of dopamine in the substantia nigra of the brain. Dopamine is produced in the brain from ι-DOPA (ι-dihydroxyphenylalanine) by removal of a molecule of carbon dioxide. The ι-DOPA is produced by oxidation of tyrosine, which is in turn produced from phenylalanine by another oxidoreductase. The enzyme that converts ι-DOPA to dopamine is best classified as an: Lyase
In a Lineweaver-Burk plot of enzyme activity, the highest values of [S] and Km are found: Near the origin
An enzyme in liver that removes glucose from blood has a high Km; another that does the same thing in brain tissue has a small Km. The usefulness of these two different values is that: The enzyme in brain tissue can take glucose from the bloodstream even when levels are low, and the enzyme in liver will not take glucose from blood unless levels are high
If you wanted to explain the concept of Km to someone who didn't know as much about as you, you might say that: Km is the substrate concentration that allows the reaction to proceed at half the maximum velocity
What happens to the active site and the molecular geometry of the enzyme as it is denatured?
Changing the shape of the active site of an enzyme will cause its reaction to slow down until the shape has changed so much that the substrate no longer fits. When this happens the reaction stops. At this point we say the enzyme isdenatured and is permanently damaged.
A competitive inhibitor of the activity of an enzyme binds to the active site of the enzyme.
An allosteric enzyme may show a sigmoid dependence on substrate concentration
A competitive inhibitor of an enzyme-catalyzed reaction is usually structurally similar to the substrate.
A prosthetic group of an enzyme participates in the reaction catalyzed by the enzyme
In a reaction catalyzed by an enzyme, the enzyme does not affect the equilibrium constant for the reaction
The binding of a substrate to an enzyme may involve hydrogen bonds and van der Waal interactions.
Enzymes have a distinct advantage over nonbiological catalysts because they: Are very efficient, specific, and sensitive to control.
Most coenzymes may be included in classes of foodstuffs known as: Vitamins.
The fact that allosteric enzymes are remarkably sensitive to control makes them ideal candidates for: The rate-limiting steps in a pathway.
If you wanted to explain the concept of Km to someone who didnBt know as much about biochemistry as you, you might say that: Km is the substrate concentration that allows the reaction to proceed at half the maximum velocity.
Most enzymes function within a narrow range of pH. Many have a closely defined optimum pH. Enzymes that function in the stomach usually have lower pH optima than those which are found in the intestine. Enzymes could be expected to be sensitive to minor pH changes because:Changes in proton concentrations result in changes in charges of acidic or basic groups, resulting in changes in the enzyme structure.
The major effect of a catalyst on a reaction is to: Lower the activation energy.
Most amino acids found in living things are ι-form amino acids. A few amino acids found in antibiotics are D-form. The enzyme that converts D-alanine to ι-alanine is best classified as an: Isomerase.
An enzyme in liver that removes glucose from blood has a high Km; another that does the same thing in brain tissue has a small Km. The usefulness of these two different values is that: The enzyme in brain tissue can take glucose from the bloodstream even when levels are low, and the enzyme in liver will not take glucose from blood unless levels are high.
As a solution containing an enzymatic reaction is heated, the temperature rises and the reaction velocity rises gradually for some period but typically falls off very rapidly after reaching the optimum temperature because: The enzyme functions more rapidly as the solution is heated because the molecules move faster, but after a certain temperature, the enzyme becomes denatured.