Download Enzyme

Enzymes
- exercise Vladimíra Kvasnicová
Each question of the test contains 4 statements (a, b, c, d). You can obtain
1 point (correct answer), –1 point (incorrect answer) or 0 point (if ? is
marked). All four statements can be either correct or incorrect or some of
the statements can be correct and some incorrect. Use the following
schema to complete the answer table:
Y = I agree with the statement
N = I disagree with the statement
? = I don't know
No
a
b
c
d
1
Y N ? Y N ? Y N ? Y N ?
2
Y N ? Y N ? Y N ? Y N ?
3
Y N ? Y N ? Y N ? Y N ?
4
Y N ? Y N ? Y N ? Y N ?
5
Y N ? Y N ? Y N ? Y N ?
Each question of the test contains 4 statements (a, b, c, d). You can obtain
1 point (correct answer), –1 point (incorrect answer) or 0 point (if ? is
marked). All four statements can be either correct or incorrect or some of
the statements can be correct and some incorrect. Use the following
schema to complete the answer table:
Y = I agree with the statement
N = I disagree with the statement
? = I don't know
No
a
b
c
d
1
Y N ? Y N ? Y N ? Y N ?
2
Y N ? Y N ? Y N ? Y N ?
3
Y N ? Y N ? Y N ? Y N ?
4
Y N ? Y N ? Y N ? Y N ?
5
Y N ? Y N ? Y N ? Y N ?
Phosphatase catalyzes
a) insertion of Pi into a substrate
b) removing of Pi from a substrate
c) hydrolysis of an ester bond
d) reaction producing ATP
Phosphatase catalyzes
a) insertion of Pi into a substrate
b) removing of Pi from a substrate
c) hydrolysis of an ester bond
d) reaction producing ATP
No
1
a
b
c
d
Y N ? Y N ? Y N ? Y N ?
hydrolase
(esterase)
dephosphorylation
(hydrolytic cleavage of an ester bond)
phosphotransferase
phosphorylation
(isertion of phosphate to a substrate)
The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations,
4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
Choose correct statements:
a) dehydrogenases catalyze oxidativereducing reactions
b) carboxylases need ATP for their
function
c) kinases transfer a phosphate from an
energy rich compound to a substrate
d) hydroxylases catalyze oxidation of a
substrate
Choose correct statements:
a) dehydrogenases catalyze oxidativereducing reactions
b) carboxylases need ATP for their
function
c) kinases transfer a phosphate from an
energy rich compound to a substrate
d) hydroxylases catalyze oxidation of a
substrate
Alcohol dehydrogenase
oxidation of a substrate without direct
presence of oxygen
(NAD+ used as a coenzyme)
The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations,
4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
Carboxylase elongates a molecule by 1 carbon (as carboxyl, COO-).
It needs CO2 disolved in water = HCO3-.
It is a ligase – it needs energy for its function: ATP is cleaved to
ADP and phosphate.
Reaction catalyzed
by glucokinase
(or hexokinase)
The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations,
4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
Hydroxylase
= monoxygenase
catalyzes an introduction
of 1 oxygen atom to a
substrate as –OH;
the second oxygen
(from molecular O2)
is reduced to H2O
The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations,
4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
Alanin aminotransferase (ALT)
catalyzes a reaction of Ala with ketoglutarate. The reaction produces
a) oxaloacetate
b) aspartate
c) glutamate
d) pyruvate
Alanin aminotransferase (ALT)
catalyzes a reaction of Ala with
-ketoglutarate. The reaction produces
a) oxaloacetate
b) aspartate
c) glutamate
d) pyruvate
Alanine aminotransferase
transfers –NH2 group from alanine to -ketoglutarate
(alanine is converted to pyruvate, -ketoglutarate gives glutamate)
- reversible reaction -
The figure was adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations,
4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2
Enzyme catalyzing cleavage of a bond
between 2 amino acids in proteins
belongs among
a) lyases
b) peptidases
c) hydrolases
d) transferases
Enzyme catalyzing cleavage of a bond
between 2 amino acids in proteins
belongs among
a) lyases
b) peptidases
c) hydrolases
d) transferases
AA1
AA2
H2O
dipeptide
peptide bond
The figure is found at http://www.richmond.edu/~jbell2/04F03.JPG (Jan 2007)
Choose a corret statement(s):
a) maximal velocity Vmax is related to maximal
number of substrate molecules transformed
by the enzyme per unit of time
b) KM is expressed in velocity units (mol.s-1)
c) KM = concentration of a substrate needed to
reach ½ Vmax of the reaction
d) KM = concentration of a substrate needed for
transformation of ½ enzyme molecules to
complex enzyme-substrate
Choose a corret statement(s):
a) maximal velocity Vmax is related to maximal
number of substrate molecules transformed
by the enzyme per unit of time
b) KM is expressed in velocity units (mol.s-1)
c) KM = concentration of a substrate needed to
reach ½ Vmax of the reaction
d) KM = concentration of a substrate needed for
transformation of ½ enzyme molecules to
complex enzyme-substrate
The figure is found at http://fig.cox.miami.edu/~cmallery/255/255enz/gk3x15.gif (Dec 2006)
KM of a pair enzyme-substrate
a) is decreased by a competitive inhibitor
b) is equal to the concentration of a substrate
when an activity of the enzyme is maximal
c) is increased by a noncompetitive inhibitor
d) is directly proportional to an affinity of the
enzyme to its substrate
KM of a pair enzyme-substrate
a) is decreased by a competitive inhibitor
b) is equal to the concentration of a substrate
when an activity of the enzyme is maximal
c) is increased by a noncompetitive inhibitor
d) is directly proportional to an affinity of the
enzyme to its substrate
Summary of an enzyme inhibition
The figure is found at http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/EnzymeKinetics.html (Dec 2006)
Km describes affinity of an enzyme
to its substrate
! indirect proportionality !
The figure is found at http://fig.cox.miami.edu/~cmallery/255/255enz/gk3x15.gif (Dec 2006)
Choose a correct statement(s):
a) an inhibition is competitive if an inhibitor
competes with a substrate to be bound
into an active site of an enzyme
b) a noncompetitive inhibition can be
decreased by an increasing of a substrate
concentration
c) competitive inhibitors have very often a
similar structure as a substrate
d) noncompetitive inhibitors decrease Vmax
Choose a correct statement(s):
a) an inhibition is competitive if an inhibitor
competes with a substrate to be bound
into an active site of an enzyme
b) a noncompetitive inhibition can be
decreased by an increasing of a substrate
concentration
c) competitive inhibitors have very often a
similar structure as a substrate
d) noncompetitive inhibitors decrease Vmax
Inhibition of enzymes
The figure is found at http://stallion.abac.peachnet.edu/sm/kmccrae/BIOL2050/Ch1-13/JpegArt113/05jpeg/05_jpeg_HTML/index.htm (Dec 2006)
Competitive inhibition
• inhibitor resembles
substrate
• it is bound to an active
site but not converted by
the enzyme
• increases Km (affinity of
enzyme to its S)
• if concentration of a
substrate is increased the
inhibition is decreased
• the inhibition is reversible
The figure is found at: http://www.steve.gb.com/science/enzymes.html (December 2006)
Noncompetitive inhibition
• inhibitor binds at a site other
than the substrate-binding
site
• inhibition is not reversed by
increasing
concentration of substrate
(no Km change)
• Vmax is decreased (it is related
to decreasing of active enzyme
concentration)
• reversible only if the inhibitor is
not bound by covalent bond
The figure is found at: http://www.steve.gb.com/science/enzymes.html (December 2006)
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
1
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
2
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
3
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
4
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
1
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
2
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
3
Choose the proper graph describing
a) competitive
inhibition
b) noncompetitive
inhibition
c) inhibition by
substrate excess
d) allosteric enzyme
4
Allosteric enzyme: a) monomeric, b) oligomeric
The figure is adopted from Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th
ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2