Transcription is the process by which RNA (nucleic acid that is responsible for transferring genetic information from DNA ) is synthesized from the genetic information contained in the coding regions of DNA. Therefore, a copy of complementary RNA and antiparallel to the DNA sequence that was transcribed is obtained. Normally organism synthesize RNA by a reaction catalyzed by RNA polymerases (they are enzymes that are involved in the process of DNA replication).
Transcription occurs in three steps: initiation, elongation and termination.
Initiation: Is the beginning of transcription. It occurs when the RNA polymerase enzyme binds to a region of a gene called a promoter. This tells the DNA to unwind so that enzyme can 'read' the bases in one of the strands of DNA. The enzyme is now ready to create a strand of mRNA (it is a single stranded RNA molecule, complementary to one of the DNA strands of a gene) with a complementary base of bases.
Elongation: Is the addition of nucleotides to the mRNA strand. The RNA polymerase reads the unwound strand of DNA and builds the mRNA molecule, using complementary base pairs. THere is a brief moment during this process when the new RNA molecule is bound to the unwound DNA. During this process, an adenine in the DNA binds to an uracil in the RNA.
Termination: Is the term of transcription and occurs when RNA polymerase crosses a termination sequence in the gene. The mRNA strand is complete and separated from the DNA.
