Vector Biology Multiple Choice Questions on “Restriction Endonucleases – 1”.
1. Cutting and joining of the DNA are which techniques?
A. DNA degradation
B. DNA replication
A. DNA manipulation
D. DNA synthesis
Answer: C
Clarification: 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
A. Degraded or denatured
D. Enclosed in a parent cell
Answer: B
Clarification: 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
A. Endonucleases
D. Modifying enzymes
Answer: B
Clarification: 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
A. Ligase
D. Phosphatase
Answer: A
Clarification: 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
A. DNase I
D. BamHI
Answer: C
Clarification: 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
A. DNA polymerase III
D. DNA polymerase IV
Answer: A
Clarification: 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
A. III
D. Klenow fragment
Answer: A
Clarification: 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
A. Used in complementary DNA cloning
D. Synthesizes DNA from RNA
Answer: A
Clarification: 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
A. Arctic shrimp
D. Calf thymus tissue
Answer: D
Clarification: 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
Answer: A
Clarification: 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.
11. Host controlled restriction is a phenomenon related to ________
A. Bacteria
B. Virus
A. Plasmid
D. Gene of interest
Answer: A
Clarification: The initial observation that led to the discovery of restriction endonucleases was made in early 1950s when it was shown that some strains of bacteria are immune to bacteriophage infection.
12. Why does the restriction phenomenon in bacteria naturally occur?
A. For efficient cloning
B. Bacteria produce an enzyme
A. Destruction of bacterium’s own DNA
D. For survival
Answer: B
Clarification: Restriction occurs because the bacterium produces an enzyme that degrades phage DNA before it has time to replicate and direct synthesis of new phage particles.
13. Which type of restriction endonucleases is used most in genetic engineering?
A. Type I
B. Type II
A. Type III
D. Type IV
Answer: B
Clarification: Type I and Type III are complex and have only a limited role in genetic engineering. Type II restriction endonucleases are used mostly as the cutting enzymes in gene cloning.
14. The restriction endonuclease PvuI (isolated from Proteus Vulgaris) cuts DNA at which position?
A. Hexanucleotide CGATCG
B. Random position
A. Towards the end
D. Hexanucleotide CAGCTG
Answer: A
Clarification: A particular enzymes cleaves DNA at the recognition sequence and nowhere else. PvuI cuts DNA at hexanucleotide sequence CGATCG.
15. The restriction endonuclease AluI is isolated from which microbe?
A. Proteus Vulgaris
B. Staphylococcus Aureus
A. Arthrobacter Luteus
D. Haemophilus Influenzae
Answer: C
Clarification: AluI restriction endonuclease derived from Arthrobacter Luteus, cleaves a DNA molecule at nucleotide long site- AGCT. There are other endonucleases that cleave at bigger sites.