Question

What is the effect if pBR322, a cloning vector does not carry 'ori site'?
(a) sticky ends will not produce
(b) the transformation will not take place
(c) The cell will transfer into a tumor cell
(d) replication will not take place

Answer 1

Hint: The site or sequence in a cloning vector where initiation of replication takes place and it also controls the copy number of the linked DNA.

Complete step by step answer:
The origin of replication (ori) is the sequence where replication starts. If a DNA piece is linked to this sequence, it can be made to replicate within the host cell. If the Origin of replication is absent in a cloning vector, there will be no initiation of replication.
So, the correct answer is 'replication will not take place'.

Additional information:
- The DNA which is used as a carrier for the transfer of a fragment of foreign DNA into a suitable host is called 'vector'. Vectors which are used for multiplying the foreign DNA are called cloning vectors.
Examples of cloning vectors are plasmids, bacteriophages, artificial chromosomes, and cosmids, etc.
- Apart from natural vectors, artificial plasmids like pBR322, PUC 19,101 are popularly used.
- pBR322 is an E.coli cloning vector that contains restriction sites hind III, EcoRI, BamHI, Sal I, pvu II, pst I, Cla I, ori, and antibiotic- resistant genes such as amp and tet.ori is the site where replication starts.
- Bacteria and viruses also transfer genes into plants and animals. Ex: Agrobacterium tumefaciens, a pathogen that is able to deliver a piece of DNA called 'T-DNA' to transform normal plant cells into tumor cells to produce chemicals required by the pathogen. Due to its mechanism to deliver genes, it is used as a vector.

Note: Origin of replication, apart from initiation of replication, it is also responsible for controlling the number of copies that are linked to DNA.
To make many copies of the target DNA, it should be cloned with the vector whose 'ori' supports a high copy number.