Central dogma explains how the DNA codes for the proteins which proceed in three stages, namely, replication, transcription and translation. Once DNA replicates its two strands, the information is copied into RNA by the process called transcription. Let’s learn more about the process of transcription.
It is one of the first processes in gene expression. RNA polymerase which is an enzyme copies a particular segment of DNA into RNA. Transcription Unit is a stretch of a DNA transcribed into an RNA molecule. Its function is to encode at least one gene. Suppose if gene encodes protein than mRNA is produced by a transcription.A protein encoded by DNA transcription unit may comprise a coding sequence. Compared to DNA replication, transcription has a lower copying fidelity.
Transcription of DNA into RNA is governed by the complementary base pairs of the two nucleic acids. Both DNA and RNA are complementary to each other with one exception. The thymine is replaced by uracil in RNA. During the transcriptional process, DNA-dependent RNA polymerase begins to read a segment of DNA which is transcribed into complementary RNA. As in replication, transcription also proceeds in enzymatically catalysed steps i.e. initiation, termination and elongation.
- The DNA-dependent RNA polymerase binds to the promoter and catalyses the polymerization in the 5’ to 3’ direction on the template strand.
- Once it reaches the terminator sequence, the process terminates and the newly synthesised RNA strand is released.
- The released RNA strand then undergoes post-transcriptional modifications.
The transcription of both strands of DNA would lead to the formation of two RNAs with opposite codes which can mislead the protein synthesis. In addition, if both the DNA strands are transcribed, there would be two complementary RNA strands only. This, in turn, would turn a single-stranded RNA to double-stranded RNA and this would halt the translation process. In order to avoid the complication in the genetic coding mechanism, only a single strand of a DNA is transcribed into RNA. The complexity of the process varies in different organisms based on their level of organisation.
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