1. What is the role of antisense RNA in the plasmid?
a) Formation of a hollow appendage
b) Produce antibiotic activity
c) Regulating the initiation of plasmid replication
d) Taking up of foreign DNA
Explanation: The copy number of a plasmid is determined by regulating the initiation of plasmid replication. Two major mechanisms for this include- regulation by antisense RNA and regulation by binding proteins at repeated sequences.
2. Most of the cloning vectors in current use carry an origin region from which plasmid?
a) RP4
b) Col E1
c) RSF1010
d) RP6
Explanation: In this type of plasmid, primer for replication is a 555-base ribonucleotide molecule called RNAII which forms an RNA-DNA hybrid at the origin of replication.
3. What is the role of Rop protein in a plasmid?
a) Maintaining stability
b) Antibiotic resistance
c) Maintaining copy number
d) Conversion into a shuttle vector
Explanation: This protein which forms a dimer enhances the pairing between RNAI and RNAII so that processing of the primer can be inhibited even at low RNAI concentration.
4. In the broad host-range plasmid Psc101, close to the origin, there is a gene repA. What is the importance of this gene?
a) In deciding the host
b) In transformation
c) In replication
d) In the survival of host
Explanation: repA encodes the only plasmid-encoded protein, required for replication. It binds to the iterons and initiates DNA synthesis
5. Linking two plasmids by binding to their origin sites and thereby preventing replication is known as __________
a) Transduction
b) Handcuffing
c) Conjugation
d) Transfection
Explanation: The RepA protein links two plasmids together by binding to their iteron sequences. The replication of iteron plasmid then depends on the concentration of protein and plasmid itself.
6. The par region from a plasmid such as Psc101 can be cloned into Pbr322. What is the function of this region?
a) Maintains stability
b) Maintains high copy number
c) Maintains cloning efficiency
d) Aids in replication
Explanation: Partitioning function, par regions are essential for low copy number plasmids. The higher copy number plasmids also contain a par region but this is deleted in many cloning vectors.
7. Multimeric forms of a plasmid may give rise to __________
a) Low copy number
b) High copy number
c) Plasmid instability
d) Plasmid loss
Explanation: The mechanism that controls the copy number of the plasmid ensures a fixed number of plasmid origins per bacterium. Cells containing multimeric plasmids have the same number of plasmid origins but fewer plasmid molecules which leads to segregative instability if they lack a partitioning coefficient
8. Plasmids will be incompatible if they have the same mechanism of replication control.
a) true
b) false
Explanation: Plasmid incompatibility is the inability of two plasmids to coexist in the same cell in the absence of selective pressure. They will be incompatible if they share the same partitioning function region.
9. In the purification of a plasmid DNA what will the clear lysate consist of?
a) Plasmid DNA
b) Genomic DNA
c) Buffer
d) Cell debris
Explanation: If the lysis of cell is done gently, most of the chromosomal DNA released will be of high molecular weight and can be removed along with cell debris.
10. What is the role of ethidium bromide in isopycnic centrifugation of cleared lysates?
a) Denatures genomic DNA
b) Lysis the membrane
c) Intercalates and unwinds
d) Fluoresces plasmid DNA
Explanation: EtBr binds by intercalating between the DNA basepairs and in doing so causes the plasmid DNA to unwind. Thus covalent circles can be separated from linear chromosomal DNA.