1. Col plasmids are responsible for ______
a) Degrading unusual molecules
b) Taking up colchicine stain
c) Coding for colicins
d) None
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.
2. Ti plasmids are ____ plasmids.
a) Tumor inducing
b) Degradation
c) High copy number
d) Mammalian
Explanation: Ti plasmids are tumor inducing plasmids found in Agrobacterium tumefaciens, a bacterium which infects dicot plants and causes crown gall disease in them.
3. Which of the following is responsible for the conversion of covalently closed circular DNA to supercoiled DNA of the plasmid?
a) Endonuclease
b) DNA Gyrase
c) Topoisomerase
d) Exonuclease
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.
4. Which of the forms of plasmid DNA can be differentiated by electrophoresis on agarose gel?
i. Covalently closed
ii. Open circular
iii. Supercoiled
iv. Linear
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.
5. 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.
6. Plasmids confer phenotypes to the host organism, some of the plasmids to which these phenotypic traits have not yet been ascribed are called ________
a) Unique plasmids
b) Resistance plasmid
c) Q-plasmids
d) Cryptic plasmids
Explanation: Plasmids that confer anonymous characteristics or no characteristic to the host organisms but can still be used for cloning are called cryptic.
7. Which of the following is a high copy number plasmid?
a) Conjugative plasmids
b) Stringent plasmids
c) Non-conjugative plasmids
d) F-plasmid
Explanation: Non-conjugative plasmids are high molecular weight plasmids present as multiple copies per chromosome.
8. R6K is a _______
a) Stringent plasmid
b) Non-conjugative plasmid
c) Relaxed plasmid
d) Cryptic plasmid
Explanation: R6K is a low molecular weight conjugative plasmid present in multiple copies that is it’s a relaxed plasmid.
9. Where are the genes that encode for proteins required for replication encoded in a plasmid?
a) Near origin of replication
b) Opposite to origin of replication
c) In the bacteria’s genome
d) Not present
Explanation: The replication proteins that are plasmid encoded are located very close to the origin sequences at which they act, thus only a small region surrounding the origin site is required for replication. Other parts of the plasmid can be deleted and foreign sequences can be added and replication will still occur.
10. Which of the following is not a characteristic feature of plasmid RP4?
a) A col plasmid
b) Replicates in most gram-negative bacteria
c) A conjugative plasmid
d) A promiscuous plasmid
Explanation: Col plasmids aid in bacteriocin production in an organism and RP4 is not a plasmid of that kind. All other options given are the sole characteristics of RP4 plasmids.