WorksheetsEnzymology Part II
Total questions: 27
Worksheet time: 29mins
T or F. The Michaelis constant determines the Vmax of an enzymatic reaction
(a)
Competitive inhibitors have this effect:
modifying the Km value
changing the value for Vmax
interfering with substrate binding
changes the Km and interferes with substrate binding
all of the above are correct
The value of Vmax changes in
competitive inhibition
noncompetitive inhibition
both forms of inhibition
neither forms of inhibition
Which of the following is true?
E-S complex often dissociates with no reaction taking place
E-S complex must form before a reaction can take place
once E-S complex forms, forms product or dissociates to E + S
all of these
The initial rate of an enzymatic reaction is usually determined in order to assure that
the enzyme is active
there is no reverse reaction of product to enzyme-substrate complex
the substrate is not used up
the experiment can be completed quickly
The Michaelis constant is
related to molecular weight of enzyme
a measure of the resistance of enzyme to denaturation
a refection of the percentage of polar amino acids in enzyme
a measure of how tightly substrate is bound to enzyme
An important step in elucidating the behaviour of an enzyme is
obtaining a crystalline sample of enzyme
insuring that metal ions are always excluded from enzyme
determine active site residues
none of these
The amino acids in the active site can be involved in all of these processes, except:
binding of the substrate
becoming part of the product of reaction
the actual chemical mechanism for the reaction
binding of some necessary cofactor
all of these can be functions of the amino acids in active site
What effect is seen on a Lineweaver-Burk graph when a competitive inhibitor is added
y-intercept is changed, but does not change slope
slope of line is changed but not y intercept
both slope and y intercept is changed
neither y intercept or slope of line is changed
The data shown below were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics:
V0 Substrate added
(mmol/min) (mmol/L)
217 0.8
325 2
433 4
488 6
647 1,000
What value will be the best estimate for the Km from this kinetic study?
2 mM
1 mM
4 mM
6 mM
The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by the formula
1/V0 = Km /(Vmax [S]) + 1/Vmax
To determine Km from a Lineweaver-Burk plot, you would:
multiply the reciprocal of the x-axis intercept by -1
take the x-axis intercept where V0 = 1/2 Vmax
multiply the reciprocal of the y-axis intercept by -1
take the reciprocal of the x-axis intercept
Which of the following is not a function of an enzyme?
accelerate rate of a process
lower activation enzyme of reaction
shift equilibrium between products and reactants
speed up biological processes
lower energy of transition state
FINSIHWhat is the active site of an enzyme?
is portion of substrate that enzyme binds to, initiating chemical reaction
portion of enzyme that allows enyzme to diffuse throgh plasma membrane
An allosteric inhibitor does which of the following?
binds to enzyme away from active site and changes conformation of active site, increasing affinity for substrate binding
binds to active site and blocks it from binding substrate
binds to enzyme away from active site and changes conformation of active site, decreasing affinity for substrate
binds directly to active site and mimics substrate
With regards to Michaelis-Menten equation, a molecule that has effect of increase Vmax of reaction upon binding to enzyme would be called?
competitive inhibitor
noncompetitive inhibitor
uncompetitive inhibitor
activator
Potassium cyanide is a poison, which combines with cytochrome c to prevent binding of oxygen to enzyme without altering Km. Which type of inhibition does this represent?
competitive inhibitor
non-competitive inhibitior
uncompetitive inhibitor
activator
irreversible inhibitor
Which of the following is true regarding enzymes saturated with substrate?
an enzyme with lower Km is more easily saturated than enzyme with high Km
at saturating levels of substrate, competitive inhibitor will affect reaction rate more than non-competitive inhibitor
any excess substrate will shift the equilibrium towards product end of reation
increasing substrate concentration will appreciably increase reaction rate
S-Adenosyl methionine (SAM) is molecule utilised in various metabolic pathways to transfer methyl groups from SAM to acceptor. What is the proper designation of complex of SAM and its enzyme together?
prosthetic group
coenzyme
holoenzyme
cofactor
In the first step of glycolysis, hexokinase produces glucose-6-phosphate. G-6-P itself can also bind to hexokinase at the active site, blocking access to ATP. This is an example of:
uncompetitive inhibition
allosteric inhibition
non-competitive inhibition
feedback inhibition
Which of the following would have the weakest conjugate acid?
a strong base
a weak base
a weak acid
a strong acid
Vmax for an enzyme-catalyzed reaction:
generally increases when pH increases.
increases in the presence of a competitive inhibitor.
is limited only by the amount of substrate supplied.
is twice the rate observed when the concentration of substrate is equal to the Km.
The role of serine at the active site of serine proteases is to act as a(n) (a) catalyst, while the histidine residue serves as a(n) acid-base catalyst.
The catalytic triad of chymotrypsin and other serine proteases consists of
three amino acid residues close enough in space to make serine a strong nucleophile
three enzymes with very similar structural features
three amino acid residues adjacent in the primary structure which act to make serine a strong nucleophile
three subunits of the enzyme
It is difficult to determine either Km or Vmax from a graph of velocity vs. substrate concentration (saturation curve) because
an asymptotic value must be determined from the graph
the points on the graph are often not spread out on the hyperbola
the graph is sigmoidal
too much substrate is required to determine them
T or F. General acid & base catalysis involves groups which donate or accept protons without forming a covalent bond
(a)
T or F. Covalent catalysis involves nucleophilic attachment (electron donation) and results in a transient covalent bond
(a)
T or F. Metal ion catalysis introduce ionic interactions which assist in orientation of substrate or stabilise charges during transition states
(a)
