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 a b c d

1 Y N ? Y N ? Y N ? Y N ?

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

dephosphorylation phosphorylation(hydrolytic cleavage of an ester bond) (isertion of phosphate to a substrate)

hydrolase phosphotransferase (esterase)

Choose correct statements:

a) dehydrogenases catalyze oxidative-reducing 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 oxidative-reducing 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

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

Alcohol dehydrogenase

oxidation of a substrate without direct presence of oxygen

(NAD+ used as a coenzyme)

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.

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

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

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

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

Alanine aminotransferase

transfers –NH2 group from alanine to -ketoglutarate(alanine is converted to pyruvate, -ketoglutarate gives glutamate)

- reversible reaction -

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

The figure is found at http://www.richmond.edu/~jbell2/04F03.JPG (Jan 2007)

H2O

AA1 AA2

dipeptide

peptide bond

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

The figure is found at http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/EnzymeKinetics.html (Dec 2006)

Summary of an enzyme inhibition

The figure is found at http://fig.cox.miami.edu/~cmallery/255/255enz/gk3x15.gif (Dec 2006)

Km describes affinity of an enzymeto its substrate

! indirect proportionality !

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

The figure is found at http://stallion.abac.peachnet.edu/sm/kmccrae/BIOL2050/Ch1-13/JpegArt1-13/05jpeg/05_jpeg_HTML/index.htm (Dec 2006)

Inhibition of enzymes

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)

• 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)

Noncompetitive inhibition

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme1

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme2

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme3

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme4

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme1

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme2

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme3

Choose the proper graph describing

a) competitive inhibition

b) noncompetitive inhibition

c) inhibition by substrate excess

d) allosteric enzyme4

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

Allosteric enzyme: a) monomeric, b) oligomeric