1. The nucleic acid remaining in the solution can be precipitated by addition of sodium or ammonium acetate and ethanol.
a) False
b) True
Explanation: The nucleic acid is present in the solution and is precipitated by the addition of sodium or ammonium acetate and ethanol. It is because; nucleic acid is polar in nature and thus easily dissolves in water. Hence, to avoid this sodium acetate and ethanol is added. Sodium acetate is shields the charge present on the sugar phosphate backbone and further bonds are easily formed between ethanol and phosphate. It leads to separating out of nucleic acids
2. Nucleic acid precipitated constitutes of ____________
a) plasmid DNA
b) plasmid DNA, along with RNA and chromosomal DNA
c) rna alone
d) chromosomal DNA only
Explanation: Nucleic acid precipitated contains the plasmid DNA and along with it RNA and remnants of chromosomal DNA are also present. RNA can be removed via adding RNase
3. Treatment with exonuclease leads to removal of ____________
a) remnants of chromosomal DNA
b) RNase
c) plasmid DNA which is circularized
d) proteins
Explanation: Exonuclease leads to removal of remnants of chromosomal DNA because they are usually having linear ends. The circularized ends of plasmid are protected from the action of exonuclease because they don’t have any free ends for their action
4. Adsorption onto a solid phase support followed by elution is used as an alternative for separation of which component?
a) chromosomal DNA
b) plasmid DNA
c) RNA alone
d) other impurities
Explanation: This method is used for separation of plasmid DNA. It is advantageous because it avoids the use of phenol and also removes RNA at times along with plasmid DNA.
5. Which of the following components bind to the solid column made of silica, under high salt concentration?
a) Proteins
b) Polysaccharides
c) Both proteins and polysaccharides
d) Plasmid DNA
Explanation: Plasmid DNA binds to a solid support which is made of silica and under high salt concentrations. A high salt concentration doesn’t allow less polar molecules to bind such as polysaccharides and proteins. The binded DNA molecule is further eluted by using a low salt concentration.
6. Purification of DNA by using silica derivatized groups by DEAE is termed as ____________
a) ion exchange resin based method.
b) silica based purification
c) atom based resin exchange method
d) packed bed purification
Explanation: Silica derivatized groups by DEAE are used for purification of DNA. These groups are positively charged and the DNA gets attached to it, along with other species such as RNA which are negatively charged. Further, DNA can be obtained by varying the ionic concentrations.
7. Which of the following is correct with respect to caesium chloride centrifugation?
a) Caesium is light in weight
b) The dissolution of caesium and nucleic acids leads to the formation of gradients
c) According to the amount of supercoiling and A+T content, the DNA settles
d) Nicked DNA settles below than supercoiled DNA
Explanation: Caesium chloride is heavy and when the nucleic acid is dissolved with it, density gradients are formed. According to the extent of supercoiling and G+C content, settling of DNA takes place. The nicked DNA settles above than the nicked DNA.
8. Which of the following components settles at the bottom?
a) RNA
b) Proteins
c) Nicked DNA
d) Supercoiled DNA
Explanation: The component settling at the bottom is RNA. And the proteins float on the free surface. The nicked DNA forms a band above the supercoiled form.
9. The location of plasmid DNA can be visualized by addition of:
a) bromophenol blue
b) ethidium bromide
c) ortho xylene
d) texas red
Explanation: Ethidium bromide is added before centrifugation. It is an orange-red coloured stain which gives rosy coloured bands when placed under UV light. It acts upon by intercalating between the bases
10. Gel electrophoresis separates nucleic acid molecules based on ____________
a) charge on molecules
b) size of the molecules
c) nature of the molecules i.e. whether DNA or RNA
d) chemical properties of the nucleic acids
Explanation: Gel electrophoresis separates nucleic acid molecules on the basis of their size. The nucleic acid molecules move through the gel because of the force provided by the applied electric field.