MCQ - Enzyme question and answer

In an enzyme-catalysed reaction a product (P) is produced from:

(a) inhibitor

(b) buffer

(c) substrate

(d) magnesium

(e) sodium

(c) substrate

The variation of initial rate (vo) with respect to substrate concentration in an enzyme- catalysed reaction that obeys Michaelis-Menten kinetics is described as:

(a) linear

(b) elliptical

(c) sinusoidal

(d) hyperbolic

(e) parabolic

(d) hyperbolic

In an enzyme-catalysed reaction Km is:(a) the inhibitory dissociation constant

(b) independent of substrate concentration

(c) the maximum velocity

(d) the pH of the buffer system used

(e) The concentration of substrate that gives half the maximum velocity.

(e) The concentration of substrate that gives half the maximum velocity.

In uncompetitive inhibition:

(a) the intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

(b) the slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

(c) the inhibitor has no effect on the initial rate

(d) there is no production of product

(e) the production of product is accelerated

(a) the intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

In competitive inhibition:

(a) the intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

(b) the slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

(c) the inhibitor is insoluble

(d) the double reciprocal plot (1/vo versus 1/[S]) is non-linear

(e) the production of substrate is accelerated

(b) the slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

An example of an enzyme which is regulated in the short term (minutes) by changing the amount of enzyme is:

(a) pyruvate kinase

(b) alanine aminotransferase

(c) monoamine oxidase

(d) ornithine decarboxylase

(e) glutamate dehydrogenase

(d) ornithine decarboxylase

Phosphorylase is

(a) activated by covalent modification

(b) not modified by covalent modification

(c) active with cellulose as a substrate

(d) not phosphorylated

(e) not a substrate for phosphorylase kinase

(a) activated by covalent modification

Allosteric enzymes exhibit

(a) hyperbolic kinetics

(b) linear vo versus [S] plots (c) no activity

(d) a sigmoid vo versus [S] plot

(e) time-dependent inactivation

(d) a sigmoid vo versus [S] plot

In the mechanism of action of trypsin:

(a) polysaccharide is hydrolysed

(b) polynucleotide is hydrolysed

(c) there is no activated nucleophile

(d) metal ions play a crucial role

(e) the catalytic triad (asp...his...ser) plays a crucial role

(e) the catalytic triad (asp...his...ser) plays a crucial role

Lactate dehydrogenase catalyses the NADH dependent reduction of:

(a) glutamate

(b) pyruvate

(c) inosine

(d) AMP

(e) ADP

(b) pyruvate

The effect of a competitive inhibitor can be overcome by:

(a) adding more inhibitor

(b) increasing the amount of enzyme

(c) increasing the amount of substrate

(d) decreasing the amount of substrate (e) decreasing the temperature

(c) increasing the amount of substrate

Sulphatases A and B reside in:

(a) mitochondria

(b) peroxisomes

(c) nuclei

(d) endoplasmic reticulum

(e) lysosomes

(e) lysosomes

Enzymes catalyse the chemical transformation of substrates into:

(a) Salt

(b) Water

(c) Products

(d) Free energy

(e) Enthalpy

(c) Products

The initial rate of an enzyme-catalysed reaction (vo) is equal to:

(a) Km

(b) Vmax

(c) d[P]/dt

(d) Ki

(e) Kd

(c) d[P]/dt

The Km for an enzyme-catalysed reaction is the substrate concentration that gives:

(a) One third of the maximal rate (Vmax)

(b) One half of the maximal rate (Vmax)

(c) Two thirds of the maximal rate (Vmax)

(d) Kd

(e) Ki

(b) One half of the maximal rate (Vmax)

Allosteric enzymes show:

(a) Normal hyperbolic initial rate (vo) versus substrate concentration [S] plots.

(b) No dependence on enzyme concentration.

(c) Sigmoidal plots of initial rate (vo) versus substrate concentration [S].

(d) No catalytic activity

(e) No pH dependence

(c) Sigmoidal plots of initial rate (vo) versus substrate concentration [S].

Lactate dehydrogenase catalyses the NADH dependent reduction of:

(a) Glutamate

(b) Pyruvate

(c) Inosine

(d) AMP

(e) ADP

(b) Pyruvate

The effect of a competitive inhibitor can be overcome by:

(a) Adding more inhibitor

(b) Increasing the amount of enzyme

(c) Increasing the amount of substrate

(d) Decreasing the amount of substrate

(e) Decreasing the temperature

(c) Increasing the amount of substrate

A mixed inhibitor shows:

(a) Only a slope effect in a double reciprocal (Lineweaver Burk plot)

(b) Only an intercept effect in a double reciprocal (Lineweaver Burk plot)

(c) Both a slope and intercept effect in a double reciprocal

(Lineweaver Burk plot)

(d) No dependence on the concentration of inhibitor

(e) Neither a slope nor an intercept effect in a double reciprocal plot.

c) Both a slope and intercept effect in a double reciprocal

(Lineweaver Burk plot)

An un-competitive inhibitor shows:

(a) Only a slope effect in a double reciprocal (Lineweaver Burk plot)

(b) Only an intercept effect in a double reciprocal (Lineweaver Burk plot)

(c) Both a slope and intercept effect in a double reciprocal (Lineweaver Burk plot)

(d) No dependence on the concentration of inhibitor

(e) Neither a slope nor an intercept effect in a double reciprocal plot.

(b) Only an intercept effect in a double reciprocal (Lineweaver Burk plot)

A competitive inhibitor shows:

(a) Only a slope effect in a double reciprocal (Lineweaver Burk plot)

(b) Only an intercept effect in a double reciprocal (Lineweaver Burk plot)

(c) Both a slope and intercept effect in a double reciprocal (Lineweaver Burk plot)

(d) No dependence on the concentration of inhibitor

(e) Neither a slope nor an intercept effect in a double reciprocal plot.

(a) Only a slope effect in a double reciprocal (Lineweaver Burk plot)

Regulation of an enzyme's activity by covalent modification can involve:

(a) No post-translational modification

(b) Phosphorylation, methylation or adenylation of amino acid side chains

(c) No change in catalytic activity

(d) The removal of sugar residues

(e) Depletion of substrate

(b) Phosphorylation, methylation or adenylation of amino acid side chains

Sulphatases reside in:

(a) Mitochondria

(b) Peroxisomes

(c) Nuclei

(d) Endoplasmic reticulum

(e) Lysosomes

(e) Lysosomes

Irreversible inhibitors generally show:

(a) No time dependence of the inhibition

(b) Slow time-dependent inactivation

(c) Can be removed from the enzyme by dialysis

(d) Can be removed from the enzyme by gel filtration

(e) No covalent binding to the enzyme

(b) Slow time-dependent inactivation

Enzyme assays are restricted to:

(a) Measuring the appearance of product

(b) Measuring the disappearance of substrate

(c) Measuring the appearance of product or the disappearance of substrate

(d) Those based on the use of a spectrophotometer

(e) Those based on the use of an oxygen electrode

(c) Measuring the appearance of product or the disappearance of substrate

Reversible inhibitors can be removed from an enzyme by:

(a) Dialysis

(b) Raising the temperature

(c) Lowering the temperature

(d) Freezing

(e) Concentrating the enzyme

(a) Dialysis

Proteases catalyse the hydrolysis of:

(a) Polysaccharides

(b) Phospholipids

(c) Triglycerides

(d) Nucleotides

(e) Proteins

(e) Proteins

Enzymes catalyse the chemical transformation of substrates into:

(a) salt

(b) water

(c) products

(d) free energy

(e) enthalpy

(c) products

The Km for an enzyme-catalysed reaction is the substrate concentration that gives:

(a) one third of the maximal rate (Vmax)

(b) one half of the maximal rate (Vmax)

(c) two thirds of the maximal rate (Vmax)

(d) Kd

(e) Ki

(b) one half of the maximal rate (Vmax)

Allosteric enzymes show:

(a) normal hyperbolic initial rate (vo) versus substrate concentration [S] plots.

(b) no dependence on enzyme concentration.

(c) sigmoidal plots of initial rate (vo) versus substrate concentration [S].

(d) no catalytic activity

(e) no pH dependence

(c) sigmoidal plots of initial rate (vo) versus substrate concentration [S].

Lactate dehydrogenase catalyses the NADH dependent reduction of:

(a) glutamate

(b) pyruvate

(c) inosine

(d) AMP

(e) ADP

(b) pyruvate

The effect of a competitive inhibitor can be overcome by:

(a) adding more inhibitor

(b) increasing the amount of enzyme

(c) increasing the amount of substrate

(d) decreasing the amount of substrate

(e) decreasing the temperature

(c) increasing the amount of substrate

An un-competitive inhibitor shows:

(a) only a slope effect in a double reciprocal (Lineweaver Burk plot)

(b) only an intercept effect in a double reciprocal (Lineweaver Burk plot)

(c) both a slope and intercept effect in a double reciprocal (Lineweaver Burk plot)

(d) no dependence on the concentration of inhibitor

(e) neither a slope nor an intercept effect in a double reciprocal plot

(b) only an intercept effect in a double reciprocal (Lineweaver Burk plot)

A competitive inhibitor shows:

(a) only a slope effect in a double reciprocal (Lineweaver Burk plot)

(b) only an intercept effect in a double reciprocal (Lineweaver Burk plot)

(c) both a slope and intercept effect in a double reciprocal (Lineweaver Burk plot)

(d) no dependence on the concentration of inhibitor

(e) neither a slope nor an intercept effect in a double reciprocal plot.

(a) only a slope effect in a double reciprocal (Lineweaver Burk plot)

Regulation of an enzyme's activity by covalent modification can involve:

(a) no post-translational modification

(b) phosphorylation, methylation or adenylation of amino acid side chains

(c) no change in catalytic activity

(d) the removal of sugar residues

(e) depletion of substrate

(b) phosphorylation, methylation or adenylation of amino acid side chains

Sulphatases reside in:

(a) mitochondria

(b) peroxisomes

(c) nuclei

(d) endoplasmic reticulum

(e) lysosomes

(e) lysosomes

Irreversible inhibitors generally show:

(a) no time dependence of the inhibition

(b) slow time-dependent inactivation

(c) can be removed from the enzyme by dialysis

(d) can be removed from the enzyme by gel filtration

(e) no covalent binding to the enzyme

(b) slow time-dependent inactivation

Enzyme assays are restricted to:

(a) measuring the appearance of product

(b) measuring the disappearance of substrate

(c) measuring the appearance of product or the disappearance of substrate

(d) those based on the use of a spectrophotometer

(e) those based on the use of an oxygen electrode

(c) measuring the appearance of product or the disappearance of substrate

Reversible inhibitors can be removed from an enzyme by:

(a) dialysis

(b) raising the temperature

(c) lowering the temperature

(d) freezing

(e) concentrating the enzyme

(a) dialysis

In competitive inhibition:

(a) The intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

(b) The slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

(c) The inhibitor is insoluble

(d) The double reciprocal plot (1/vo versus 1/[S]) is non-linear

(e) The production of substrate is accelerated

(b) The slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

In mixed inhibition:

(a) Only the intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

(b) Only the slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

(c) Both the slope and intercept of a double reciprocal plot (1/vo versus 1/[S])

are affected

(d) A mixture of inhibitors is used

(e) The pH of the assay medium changes

(c) Both the slope and intercept of a double reciprocal plot (1/vo versus 1/[S])

are affected

An example of an enzyme which is regulated in the short term by changing the amount of enzyme is:

(a) Lactate dehydrogenase

(b) Alanine aminotransferase

(c) Hexokinase

(d) Ornithine decarboxylase

(e) Glutamate dehydrogenase

(d) Ornithine decarboxylase

Allosteric enzymes exhibit

(a) Hyperbolic kinetics

(b) Linear vo versus [S] plots

(c) No activity

(d) A sigmoid vo versus [S] plot

(e) Time-dependent inactivation

(d) A sigmoid vo versus [S] plot

In the mechanism of action of trypsin:

(a) Polysaccharide is hydrolysed

(b) Polynucleotide is hydrolysed

(c) There is no activated nucleophile

(d) Metal ions play a crucial role

(e) The catalytic triad (asp...his...ser) plays a crucial role

(e) The catalytic triad (asp...his...ser) plays a crucial role

In an enzyme-catalysed reaction Km is:

(a) The inhibitory dissociation constant

(b) 0.1Vmaxc.

(c) 0.9Vmaxd.

(d) 100Vmaxe.

(e) The concentration of substrate that give half the maximum velocity.

(e) The concentration of substrate that give half the maximum velocity.

A useful substrate for arylsulphatase B is:

(a) glucose

(b) para-nitrophenulphosphate

(c) Nitrocatechol sulphate

(d) NADH

(e) Selenium

(c) Nitrocatechol sulphate

In uncompetitive inhibition:

(a) The intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected

(b) The slope of a double reciprocal plot (1/vo versus 1/[S]) is affected

(c) The inhibitor has no effect on the initial rate

(d) There is no production of product

(e) The production of product is accelerated

(a) The intercept of a double reciprocal plot (1/vo versus 1/[S]) is affected