The exact copy of an mRNA molecule is known as cDNA (or complementary DNA). The well-characterized cDNA molecule binds with a suitable vector which then "transforms" a bacterial cell in such a way that it does not interfere with its normal function, i.e. the vector containing the cDNA is introduced into the bacterium. The transformed bacterial cell containing a plasmid with a DNA copy of an mRNA molecule is known as a cDNA clone. It is difficult to obtain cDNA from double-stranded DNA molecules. This is why most cDNA clones have been prepared from mRNA sequences from eukaryotic cells.
A complete ORF (Open Reading Frame) clone is a plasmid that contains a DNA insert coding for a complete protein. The DNA insert contains only the protein coding sequence (from start codon to stop codon) of a complete gene (or cDNA) without the 5' and 3' untranslated regions (UTRs), or introns.