Transcription is a process in which DNA strand is converted to mRNA (messenger RNA) strand. In this process unwinding of DNA strand takes place and RNA polymerase synthesizes mRNA strand complementary to the DNA strand. At one time, only one of the DNA strand is synthesized. At the end of the transcription when mRNA is formed, post-transcriptional modification takes place where addition of a poly A tail and head takes place. Here the introns are also removed from the mRNA segment. This leads to the formation of an mRNA transcript that is ready for translation.
