<Li> After digestion of the RNA, a single stranded DNA (ssDNA) is left and because single stranded nucleic acids are hydrophobic, it tends to loop around itself . It is likely that the ssDNA forms a hairpin loop at the 3' end . </Li> <Li> From the hairpin loop, a DNA polymerase can then use it as a primer to transcribe a complementary sequence for the ss cDNA . </Li> <Li> Now, you should be left with a double stranded cDNA with identical sequence as the mRNA of interest . </Li> <P> Complementary DNA is often used in gene cloning or as gene probes or in the creation of a cDNA library . When scientists transfer a gene from one cell into another cell in order to express the new genetic material as a protein in the recipient cell, the cDNA will be added to the recipient (rather than the entire gene), because the DNA for an entire gene may include DNA that does not code for the protein or that interrupts the coding sequence of the protein (e.g., introns). Partial sequences of cDNAs are often obtained as expressed sequence tags (EST). </P>

When is complementary dna produced in the body