Question

Which of the following are essential features of a cloning vector used to create transgenic organisms:
1.Presence of ori site
2.Presence of selectable markers
3.Presence of restriction endonuclease recognition sites

• A. Only 1 and 2
  
• B. Only 2 and 3
• C. 1, 2 and 3
  
• D. Only 3
  

Answer 1

The correct option is C 1, 2 and 3


A nucleotide sequence which acts as a vehicle carrying the gene of interest into the host cell is called a vector. These vectors help in creating copies of the gene of interest. Thus they are called cloning vectors.
A cloning vector with the gene of interest inserted in it is called a recombinant DNA. An organism that contains the recombinant DNA is called transgenic organism.
Thus the cloning vectors must have the following features, for it to be used in recombinant DNA technology and produce transgenic organisms.

1. Presence of an ori (origin of replication) site to enable self replication. This is a specific sequence of nucleotides that is recognised by the helicase enzyme during replication of DNA. Thus, ORI site is the sequence at which replication is initiated in a DNA molecule.

2. Presence of selectable markers such as antibiotic resistance genes which would help in the selection of recombinant cells over non-recombinant cells.

3. Presence of specific palindromic sequences which serve as the restriction endonuclease recognition sites. Palindromic sequences are specific sequences within the DNA that read the same whether read from 5’ to 3’ or from 3’ to 5’direction. The restriction endonucleases can recognise these sequences and make cuts at specific locations of these palindromic sequences.