Question

Which one among the following is just a cloning plasmid NOT an expression plasmid?
A. pBAD 18-Cam
B. pBCSK
C. pUC 18
D. pET

Answer 1

A cloning plasmid is a DNA molecule which can replicate in a suitable host, and into which, a fragment of foreign DNA can be introduced. Whereas, expression vectors have the properties of a cloning vector, as well as contains sequences that direct expression of the inserted DNA sequence in an appropriate host organism.

Complete answer: A plasmid is a small, extrachromosomal DNA molecule within a cell that can replicate independently of the chromosomal DNA. They mostly occur as small circular, double-stranded DNA molecules in the cytoplasm of a bacterium. Expression plasmids are extracted to carry expression signals to ensure maximum expression of the foreign gene. pBAD-18-Cam, pBCSK and pET are expression plasmids that carry strong promoter and termination codons to ensure maximum gene expression. pUC19, on the other hand, is a cloning vector-only and does not carry the sequences to facilitate gene expression. The difference between cloning plasmid and expression plasmid is that the cloning plasmid is used for cloning purpose and expression plasmid is used for protein expression or gene expression in cells. For the production of proteins, expression vectors are used as a basic tool in biotechnology. Plasmids occur in the form of circular DNA. It occurs only in bacteria and not in plant or animal cells.
Hence, the correct answer is option C.

Note: A typical cloning vector consists of an origin of replication, restriction sites, antibiotic resistance genes and a reporter gene. Whereas, an expression vector consists of enhancers, promoters, termination sequences, transcription and translation initiation sites along with cloning vector features.