1. Cutting and joining of the DNA are which techniques?
a) DNA degradation
b) DNA replication
c) DNA manipulation
d) DNA synthesis
Explanation: Cutting and joining are examples of manipulative techniques most often used in the construction of recombinant DNA molecule. To produce this molecule, the vector and the DNA to be cloned must be cut at specific points and then joined together in a controlled manner.
2. What type of DNA enzymes is made use of in most of the DNA manipulative techniques?
a) Partially degraded
b) Purified
c) Degraded or denatured
d) Enclosed in a parent cell
Explanation: Although the enzymatic reactions such as DNA replication and transcription, recombination between different DNA molecules, are often straightforward but are impossible to perform by standard chemical methods. Purified enzymes are therefore crucial to genetic engineering.
3. Enzymes that remove nucleotides one at a time from the end of a DNA molecule are called ____________
a) Ligases
b) Exonucleases
c) Endonucleases
d) Modifying enzymes
Explanation: Nucleases degrade the DNA molecules by breaking the phosphodiester bonds that link one nucleotide to another in a DNA strand. There are two different kinds of nucleases.
4. The enzyme Bal31 purified from the bacterium Alteromonas Espejiana is an example of which enzyme?
a) Exonuclease
b) Endonuclease
c) Ligase
d) Phosphatase
Explanation: Bal31 removes nucleotides from both ends of a double stranded molecule. The greater the length of time that Bal31 is allowed to act on a group of DNA molecules, the shorter the resulting fragments will be endonuclease.
5. Which endonuclease cleaves both single and double stranded DNA molecules, in a non-specific manner?
a) S1
b) Bal31
c) DNase I
d) BamHI
Explanation: DNase I, prepared from cow pancreas cuts both single and double stranded molecules. DNase I is a non-specific in that it attacks at any internal phosphodiester bond, so the end result of prolonged DNase I action is a mixture of mononucleotides and very short oligonucleotides.
6. Klenow fragment is the modified enzyme of which of the parent DNA polymerase?
a) DNA polymerase I
b) DNA polymerase II
c) DNA polymerase III
d) DNA polymerase IV
Explanation: DNA pol I attach to a short single-stranded region in a double-stranded DNA molecule and then synthesize a completely new strand, degrading the existing strand as it moves forward. Hence it possesses both nuclease and polymerase activity. Removal of the segment controlling nuclease activity renders the enzyme modified and it is then called Klenow fragment.
7. The Taq DNA polymerase is DNA polymerase _________ enzyme from the bacterium Thermus aquaticus.
a) I
b) II
c) III
d) Klenow fragment
Explanation: Taq DNA polymerase is used in polymerase chain reaction and is DNA polymerase I enzyme. It is highly thermostable and is hence used in PCR.
8. Which of the following statement is not true in case of DNA Polymerase- Reverse transcriptase?
a) Involved in the replication of bacteriophage
b) Uses RNA as a template
c) Used in complementary DNA cloning
d) Synthesizes DNA from RNA
Explanation: Reverse transcriptase is involved in the replication of several kinds of viruses. Reverse transcriptase is unique in that it uses as a template not DNA but RNA.
9. Which of the following is not a source of alkaline phosphatase enzyme?
a) E.coli
b) Calf intestinal tissue
c) Arctic shrimp
d) Calf thymus tissue
Explanation: Alkaline phosphatase which removes the phosphate group present at the 5’ terminus of a DNA molecule is found in E.coli, calf intestinal tissue, arctic shrimp. Calf thymus tissue whereas is the source of another DNA modifying enzyme- Terminal deoxynucleotidyl transferase.
10. The DNA to be cloned must be cleaved along with the vector and with the same restriction enzymes.
a) true
b) false
Explanation: Large DNA molecules have to be broken down to produce fragments small enough to be carried by the vector. Most of the cloning vectors are very inefficient in carrying DNA more than 8kb in length.