Enzyme Technology Multiple Choice Questions on “Enzymes Purification – Ammonium Sulphate Fractionation”.
1. Enzyme are soluble in aqueous medium.
A. True
B. False
Answer: A
Clarification: The above statement is true because of presence hydrophilic amino-acid sidechains facing outward that interact with water molecules in the surrounding. The hydrophilic sidechains are provided by 20 different amino-acids divided in 3 types of amino acids: basic, acidic and neutral.
2. Which of these is not a basic amino-acid?
A. Arginine
B. Histidine
C. Aspartate
D. Lysine
Answer: C
Clarification: Basic amino-acids are those which have basic sidechains at neutral pH, whereas acidic amino-acids are those which have acidic side chains at neutral pH. Arginine, histidine and lysine are basic amino-acids as they contain nitrogen as sidechain and resemble ammonia which is base. Aspartate and Glutamate are acidic amino-acids as they have carboxylic acids groups as their side chain.
3. __________ is an acidic amino acid.
A. Lysine
B. Glutamate
C. Glutamine
D. Serine
Answer: B
Clarification: Acidic amino-acids are the one which have carboxylic groups as their side chains. Such two acidic amino acids ae aspartate and Glutamate. Basic amino acids are arginine, histidine and lysine. These contain ammonia as base in the side chains. Hence the name. When there is no extra acidic or basic group attaching as sidechains, the amino-acids are called neutral amino acids. Serine, Glutamine, threonine etc., are neutral amino acids.
4. Pick odd one out.
A. Histidine
B. Cysteine
C. Threonine
D. Tyrosine
Answer: A
Clarification: 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.
5. 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
Answer: B
Clarification: 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.
6. Ammonium sulphate is convenient and effective chemical for fractionation by salting out method.
A. True
B. False
Answer: C
Clarification: 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.
7. Which one of the following cannot be used as alternative to ammonium sulphate?
A. Lysozyme
B. Methanol
C. Acetone
D. Propan-2-ol