# Enzyme Technology Questions and Answers – Determination of Molecular Weight of Enzymes

This set of Enzyme Technology online test focuses on “Determination of Molecular Weight of Enzymes”.

1. Which of the following methods cannot be used to determine the molecular weight of enzymes?
a) Mass spectrometry
b) Gel filtration
c) Biosensors
d) Ultracentrifugation

Explanation: Biosensors cannot be used to determine molecular weight of enzymes. But, they are analytical devices which converts a biological response into an electrical signal. Mass spectrometry, gel filtration, ultracentrifugation are the methods used to determine the molecular weight of enzymes.

2. The method for determining molecular weight based on the size is __________
a) mass spectrometry
b) ultracentrifugation
c) gel filtration
d) biosensor

Explanation: The method for determining molecular weight based on the size is gel filtration. Ultracentrifugation is method that determines the molecular weight based on the sedimentation rate of particles. Mass spectrometry is a method to determine molecular weight based on the charge to mass ratio. Biosensor is an analytical device which converts a biological response into an electrical signal.

3. In which of the following techniques, a packed column is calibrated by applying known molecular weight enzyme to find out the molecular weight of a new enzyme?
a) Mass spectrometry
b) Ultracentrifugation
c) Gel filtration
d) SDS-gel electrophoresis

Explanation: In gel filtration, a packed column is calibrated by applying known molecular weight enzyme and then the volume of buffer required to elute out a protein is determined. The absorbance peak is measured at 280nm for each protein leaving the column. From this, a plot of elution volume versus molecular weight is drawn. Thus the unknown enzyme molecular weight is determined from the plot.

4. What is represented in the following equation?
$$M_r=\frac{RTS}{D(1-Vρ)}$$
a) Svedberg equation
b) Miachelis Menten equation
c) Arrhenius equation
d) Turn over number

Explanation: The equation, $$M_r=\frac{RTS}{D(1-Vƍ)}$$ represents the Svedberg equation which is used in determination of molecular weight by ultracentrifugation. In the above equation,
Mr = Molecular weight, R = Universal gas constant, S = Svedberg constant, D = Diffusion constant, V = partial specific volume of the molecule, ƍ = density.

5. Which of this is not a part of a mass spectrometer?
a) Ion source
b) Biocatalyst
c) Mass analyzer
d) Detector

Explanation: Biocatalyst is used on biosensor to convert substrate to product, and not mass spectrometer. Mass spectrometer is used to determine molecular weight based on the charge to mass ratio. There are 3 main parts of the mass spectrometer:
• Ion source: The sample is vaporized into a gas and then ionized by the ion source, usually by losing an electron to become a cation.
• Mass analyzer: The ions are then accelerated through a potential difference and focused into a beam to give all species the same kinetic energy.
• Deflection: The ion beam passes through a magnetic field which bends the charged stream.
• Detector: The number of ions at different deflections are counted by the detector.
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6. Which of the following method to determine molecular weight uses SDS?
a) Mass spectrometry
b) Ultracentrifugation
c) Gel filtration
d) SDS-gel electrophoresis

Explanation: SDS is an anionic detergent whose hydrocarbon chain can be linked to hydrophobic regions in the interior part of proteins liberating SO3 into the medium. These SDS molecules attach to single proteins and give it a negative charge. Hence when subjected to electrophoresis, all the proteins should travel together, but it doesn’t occur and the proteins will be separated based on the size.

7. In which of the following technique, the system is calibrated by using markers of known molecular weight to determine the unknown molecular weight?
a) Mass spectrometry
b) Ultracentrifugation
c) Gel filtration
d) SDS-gel electrophoresis

Explanation: In SDS-gel electrophoresis, the system is calibrated by using markers of known molecular weight to determine the unknown molecular weight. Whereas in gel filtration the column is calibrated with known molecular weight proteins and the elution volume of each protein is found and, hence the unknown molecular weight is determined. Mass spectrometer is based on the charge to mass ratio, whereas ultracentrifugation is based on the sedimentation rate of spherical particles.

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