This set of Vector Biology Multiple Choice Questions & Answers (MCQs) focuses on “Plasmids – 1”.
1. Which of the following is true for a plasmid?
a) Contains an origin of replication
b) Imparts a useful characteristic to the host bacterium
c) Possesses one or more genes
d) Replicates only when the host genome is undergoing replication
Explanation: A plasmid replicates independently of the host genome and this is the property exploited in cloning. All other options given are characteristic features of a plasmid.
2. What are the possible ways through which a plasmid can replicate?
a) Using cell’s own replicative enzymes
b) Carry genes that code for special replicative enzymes
c) Replicate by inserting themselves into a bacterial chromosome
d) Carry genes that codes enzymes
Explanation: A plasmid depending upon its size and host bacterium can replicate in either of the stated ways. An episome is a plasmid that inserts itself in the host bacterium and is then capable of replication.
3. Which among the following are the smallest plasmid and an ideal cloning vector?
Explanation: Puc8 is the smallest plasmid being 2.1 kbp in length and having 1.8 MDa molecular mass. The plasmid is present in bacterium E.coli and is one of the initial cloning vectors.
4. The number of molecules of an individual plasmid that are normally found in a single bacterial cell is known as?
a) Conjugative ability
c) Replicative ability
d) Copy number
Explanation: Copy number of a plasmid is particularly important as far as cloning is concerned, it gives an estimate of the yield of the desired DNA or protein product that can be anticipated.
5. What are relaxed plasmids?
a) The ones having copy numbers above 50 per cell
b) The ones that can’t be digested by endonucleases
c) The ones that can’t be isolated
d) The ones present in more than one strains of the same host
Explanation: Relaxed plasmids, regarded as the best cloning vectors have high copy numbers, present in more than 50 copies per cell. Relaxed plasmids are usually non-conjugative.
6. How can conjugative and non-conjugative plasmids be differentiated?
a) On the basis of size
b) Presence of antibiotic resistance
c) Number of cloning and digestion sites
d) Presence of transfer genes
Explanation: Transfer genes present on the conjugative plasmids can help them differentiate from the non-conjugative plasmids.
7. To be able to coexist in the same cell, different plasmids must be ______
b) Of high copy number
c) Stable at high temperatures
Explanation: Only compatible plasmids can coexist in the same cell if two plasmids are incompatible one or the other will be rapidly lost from the cell. In cloning this phenomenon is undesirable.
8. Which of the following is not a type of plasmid?
Explanation: T4 is a bacteriophage, a virus which is also a desirable cloning vector just like a plasmid. T4 can be used in higher organisms and has a lysogenic life cycle and hence a vector of choice.
9. Which characteristics do F-plasmids confer to the host bacterium?
a) Antibiotic resistance
b) Fluorescent colonies
c) Conjugative ability
Explanation: F-plasmids or fertility plasmids are responsible for providing a conjugative ability to the bacterium. Conjugation is the process by which genetic material transfer takes place between two bacteria when they come in contact through a hollow appendage on the surface joining the two plasmids.
10. Degradative plasmid TOL, responsible for the metabolism of toluene is present in which of the organisms?
b) Saccharomyces Cerevisiae
c) Staphylococcus Aureus
d) Pseudomonas putida
Explanation: Degradative plasmids aid the host organism in metabolizing unusual molecules such as toluene and salicylic acid. TOL is specifically a plasmid of Pseudomonas putida.
11. Col plasmids are responsible for ______
a) Degrading unusual molecules
b) Taking up colchicine stain
c) Coding for colicins
Explanation: Col plasmids are antibiotic plasmid types, coding for colicines the proteins that kill other bacteria. There are five types of plasmids and this is one of them, contains a selectable marker.
12. Ti plasmids are ____ plasmids.
a) Tumor inducing
c) High copy number
Explanation: Ti plasmids are tumor inducing plasmids found in Agrobacterium tumefaciens, a bacterium which infects dicot plants and causes crown gall disease in them.
13. Which of the following is responsible for the conversion of covalently closed circular DNA to supercoiled DNA of the plasmid?
b) DNA Gyrase
Explanation: If both strands of DNA are intact, it is in a relaxed form called CCC DNA, if only one strand is intact it is called open circular DNA. When isolated from cells covalently closed circles (CCC DNA) often have a deficiency of turns in the double helix, such that they have a supercoiled configuration.
14. Which of the forms of plasmid DNA can be differentiated by electrophoresis on agarose gel?
i. Covalently closed
ii. Open circular
a) i, ii, iii
b) ii, iii, iv
c) i, iii, iv
d) i, ii, iii, iv
Explanation: Open circular is the DNA with one strand intact which might not have been completely digested by an endonuclease, supercoiled DNA which is degraded upon isolation and hence falls short of turns and the linear DNA which is completely digested on both the strands by an endonuclease.
15. Protection by covalent attachment of proteins in a plasmid, is a method for?
a) increasing the conjugative abilities
b) protection of linear DNA
c) increasing the copy number
d) increasing cloning efficiency
Explanation: Not all plasmids exist as circular molecules, linear plasmids have been found in some species and to protect them, methods are: repeated sequences ending in terminal DNA hairpin loop or the ends are protected by covalent attachment of a protein.
Sanfoundry Global Education & Learning Series – Vector Biology & Gene Manipulation.
To practice all areas of Vector Biology & Gene Manipulation, here is complete set of 1000+ Multiple Choice Questions and Answers.