1. Pick odd one out.
a) Histidine
b) Cysteine
c) Threonine
d) Tyrosine
Explanation: Histidine is odd one out as it is a basic amino-acid. If the side chain attached is a basic group, the amino-acid is called basic amino-acid. Cysteine, threonine and tyrosine are neutral amino acids. If the sidechain attached has no extra basic or acidic group, the amino-acid is referred to as neutral amino-acid.
2. When the enzyme solubility is reduced by reducing the water availability, the enzyme-enzyme interaction start to take place and they will aggregate to form precipitates. This phenomenon is called ______________
a) salting in
b) salting out
c) precipitation
d) chromatography
Explanation: Salting in is a phenomenon wherein addition of salt to enzyme solution doesn’t make any difference. Hence no aggregates and no precipitates. Salting out refers to a phenomenon wherein the addition of salts reduce the water availability and in turn reducing enzyme solubility. Due to which enzyme-enzyme interaction starts. This will leads to aggregation of enzymes to form precipitates. The complete procedure is carried out at low temperatures to avoid denaturation of enzymes. Precipitation and chromatography are the steps involved in enzyme purification.
3. Ammonium sulphate is convenient and effective chemical for fractionation by salting out method.
a) True
b) False
Explanation: Salting out phenomenon is best carried out by ammonium sulphate. Hydrophobic enzymes concentrate at low salt concentrations compared to hydrophilic enzymes. The above statement is true because of its high solubility, cheapness, lack of toxicity to most enzymes and its stabilizing effect on some enzymes.
4. Which one of the following cannot be used as alternative to ammonium sulphate?
a) Lysozyme
b) Methanol
c) Acetone
d) Propan-2-ol
Explanation: Lysozyme is an enzyme which catalyzes the linkage between NAG and NAM of bacterial peptidoglycan. Hence it cannot be used as alternative to ammonium sulphate. Methanol, acetone and propan-2-ol can be used as alternative as they reduce the solubility of the enzyme by reducing dielectric constant of the medium.
5. What does the equation, logS=Kintercept-Ksalt T represent?
a) Michalis Menton equation
b) Arrhenius equation
c) Lineweaver Burk equation
d) Solubility of an enzyme
Explanation: The equation, logS=Kintercept-Ksalt T represents the solubility of an enzyme where
S = Enzyme solubility
Kintercept = Intercept constant
Ksalt = Salting out constant
T = Ionic strength which is proportional to concentration of precipitating salt
The above equation may also provide with the minimum salt concentration necessary before the enzymes start precipitating.
6. The process in which there is a free flow low molecular weight compounds across the membrane retaining high molecular weight compound is referred to as _____________
a) purity checking
b) dialysis
c) salting out
d) precipitation
Explanation: Purity checking and precipitation are the steps involved in purification. Salting out is a phenomenon to precipitate the enzyme by reducing its solubility by reducing the available water content. Dialysis uses a membrane to allow free flow of low molecular weight compounds retaining the high molecular weight compounds inside.
7. Which of the following factors does not limit the rate of dialysis?
a) Dialysis membrane relative surface area
b) Retentate volume to diffusate volume
c) Type of substance
d) Diffusible substance concentration outside the membrane
Explanation: The rate limiting factors for dialysis are as follows:
(i) Relative surface area of the membrane available for dialysis
(ii) The volume of the solution being dialyzed inside (retentate) to that of the solution outside (diffusate)
(iii) Concentration of diffusible substances outside the membrane.
The type of substance being dialyzed has no effect on rate of dialysis.
8. Which one of the following is not true for membrane selection?
a) Membrane should be highly polymerized thin films
b) Membrane should swell in presence of solvent
c) Volume of the solution being dialyzed by the membrane
d) Membrane should be chemically inert.
Explanation: The one statement which is not true for membrane u volume of the solution being dialyzed by the membrane. As this one of the rate limiting factors for dialysis. Dialysis membranes should be in the form of thin films made up of highly polymerized materials, which swell in the presence of solvent allowing low molecular weight substances to pass while preventing high molecular weight substances. The membrane should be chemically inert and without fixed charged groups.
9. Pick odd one out.
a) Animal membrane
b) Polyethylene
c) Ammonium sulphate
d) Cellophane tubing
Explanation: The odd one of the above is ammonium sulphate which is used to precipitate proteins. Whereas animal membrane, polyethylene and cellophane tubing are used as dialysis membrane which helps in removing ammonium sulphate. Collodion and colloids deposited in porous pot are also used as dialysis membrane.
10. The simplest way to remove ammonium sulphate from the system is _____________
a) precipitation
b) dialysis
c) chromatography
d) purity checking
Explanation: Dialysis uses a cellophane tubing membrane which allows ammonium sulphate to enter and not the enzymes (proteins) which are high in molecular weight. Hence it is the simplest method. Precipitation, chromatography and purity checking are the steps involved in purification.