BCH 361 EXAM 2 QUESTIONS WITH ALL VERIFIED ANSWERS
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BCH 361
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BCH 361
BCH 361 EXAM 2 QUESTIONS WITH ALL VERIFIED ANSWERS
What is the purpose of the oxyanion hole in chymotrypsin? - Answer-The oxyanion hole is a structure at the active site of chymotrypsin that stabilizes the tetrahedral intermediate in the proteolysis reaction and facilitates the formation of the a...
BCH 361 EXAM 2 QUESTIONS WITH
ALL VERIFIED ANSWERS
What is the purpose of the oxyanion hole in chymotrypsin? - Answer-The oxyanion hole
is a structure at the active site of chymotrypsin that stabilizes the tetrahedral
intermediate in the proteolysis reaction and facilitates the formation of the acyl-enzyme
intermediate.
What caused a "burst" of activity followed by a steady-state reaction when chymotrypsin
was studied in the milliseconds subsequent to mixing the enzyme and substrate? -
Answer-Chymotrypsin cleaves peptide bonds in a two-step reaction, in which the first
step, the formation of the acyl-enzyme intermediate, is faster than the second step,
hydrolysis.
If chymotrypsin is such an effective protease, why doesn't it digest itself? - Answer-
Chymotrypsin recognizes large hydrophobic groups, which are usually buried in the
enzyme's core owing to the hydrophobic effect.
Covalent Catalyst - Answer-the active site is briefly covalently modified.
acid bas catalyst - Answer-an amino acid residue at the active site of the enzyme
donates or accepts a proton.
metal ion catalyst - Answer-metal ion (+1, +2, +3) cofactors
Catalysis by approximation and orientation - Answer-the enzyme brings two substrates
together in an orientation that facilitates reaction.
What kind of catalyst do amino acid residues participate in? - Answer-acid base catalyst
these include: glutamate, Asparatate, lysine, arginine, cysteine, histidine, serine,
tyrosine
Metal ion catalyst may... (4 points) - Answer-act as an electrophilic catalyst in reduction-
oxidation reactions,
stabilizing a negative charge on the reaction intermediate,
increase the acidity of a nearby molecule,
increase the binding energy with substrate.
Temperature enhances the rate of enzyme catalyzed reactions, however, too high
temperature causes what - Answer-denaturation of the enzyme
Tyrosinase is an enzyme that catalyze the - Answer-black pigment formation.
EX: cat that has some black pigment but mostly white has a low tolerant to heat
,Enzymes isolated from thermophilic archaea are very important biochemical and
bioengineering tools as they have very good - Answer-resistance to high temperatures
The optimal pH of an enzyme varies but it is correlated with what? - Answer-the
environment of the enzyme
Two types of inhibition in terms of reversibility: - Answer-reversible inhibition and
irreversible
Three types of reversible inhibition - Answer-Competitive inhibition
Uncompetitive inhibition
Noncompetitive inhibition
They differ by the modes of inhibitor-enzyme interactions and the changes of the
enzyme kinetics.
Competitive Inhibitor binds - Answer-to the same site as the substrate thus excludes the
substrate.
Uncompetitive inhibitor binds to - Answer-the enzyme-substrate complex to form a
tertiary complex (E-S-I) which cause the enzyme to lose its activity.
noncompetitive inhibitor binds to - Answer-the enzyme at a different site from the
substrate, both to the E or ES, that affect the activity.
In competitive inhibition what happens to Km and Vmax - Answer-KM is increased in the
presence of inhibitor. (as the Inhibitor pulls the ES equilibrium backward)
Vmax of the enzyme is unchanged. The inhibition can be overcome by a sufficiently
high concentration of substrate (as the inhibitor will be displaced).
In competitive inhibition what happens with higher [I] and [S]? - Answer-Higher [I] shifts
the kinetic curve to the right.
Sufficiently high [S] can completely relieve competitive inhibition to reach the same
Vmax.
Is product formed in uncompetitive inhibition? - Answer-In uncompetitive inhibition, the
enzyme-inhibitor-substrate ternary complex does not form product.
What happens to Vmax and Km in uncompetitive inhibition? - Answer-Consequently, in
the presence of uncompetitive inhibitor, Vmax is lower and the KM is also lower
(Inhibitor drives the ES equilibrium forward)
Uncompetitive inhibition cannot be overcome by the addition of excess substrate.
, Kinetics of uncompetitive inhibition - Answer-The apparent KM (KMapp) is lowered (or it
seems result in a stronger ES binding)
Is a product formed from noncompetitive inhibition? - Answer-3. In noncompetitive
inhibition, the inhibitor can bind to both the free enzyme and the enzyme-substrate
complex. In either case, the binding of inhibitor prevents the formation of product (due to
a distortion of the active site).
What happens to Vmax and Km in noncompetitive inhibition? - Answer-Vmax is lower in
the presence of a noncompetitive inhibitor. The enzyme seems to present in a lower
concentration.
But the apparent KM is not changed as the substrate can bind to both the E and EI
equally.
The specificity of an enzyme is due to the precise interaction of the substrate with the
enzyme. This precision is a result of - Answer-the intricate three-dimensional structure
of the enzyme protein.
Enzymes are the ____ of biological systems - Answer-catalysts
Catalysts are chemicals that - Answer-enhance the rate of the reaction without
permanently being affected themselves
______________ whose active site can be modified by environmental signals - Answer-
allosteric enzymes
Enzymes are characterized by their _____ and _______ and ________. - Answer-
catalytic power; specificity to substrate; type of reaction
Enzymes are specific both in the _____ they catalyze and in their choices of _______ -
Answer-reactions; substrate
Proteolytic enzymes catalyze the hydrolysis of _______. What is the reverse reaction? -
Answer-hydrolysis of peptide bonds (aid in digestion and degradation of proteins).
-The reverse reaction is peptide bond formation, the forward reaction (hydrolysis) is
thermodynamically favored, but very slow without enzymes.
Enzymes speed up the rate of chemical reactions, but
Enzymes do not alter the - Answer-free energy change ΔG of a reaction.
Oxidoreductases - Answer-These enzymes transfer electrons between molecules. In
other words, these enzymes catalyze oxidation-reduction reactions.
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