Transcription refers to the transfer of genetic information from a DNA molecule with two-strands to an RNA molecule with one-strand. This is the process known as RNA synthesis. Interphase is when the chromosomes have stretched forms. Transcription occurs in this phase.

1. Transcriptional mechanism of prokaryotes

Three phases can be classified as Transcription: initiation (elongation), and termination.

Phase I: A segment of DNA (gene) is separated into two single strands by the enzyme RNA polymerase. This is the template phase for RNA synthesis.

Extended phase

• Each nucleotide of the template strand is combined with 1 ribonucleotide by the enzyme RNA–polymerase when it moves on the template strand according to the principle complementarity (A–U, T–A, G–X, X–G).
• The enzyme is directed in the 3’ => 5’ direction, while the RNA strand synthesized in 5’ => 3’ direction.

End stage

• The RNA-polymerase enzyme stops when it meets the termination signal. The template is then released and the RNA is completed synthesizing. Two DNA strands linked together.
• The process for RNA synthesis follows the principle of complement/template. Therefore, the sequence of nucleotides in the DNA template strand determines which sequence of ribonucleotides are on the mRNA template strand.
• The mechanism for synthesis of tRNA or rRNA is very similar to that of the mRNA. After being synthesized, the polyribonucleotide-strands of tRNA or rRNA will form a more complex structure that can be used to create an RNA molecule.

2. Transcription in the eukaryotes.

The transcription in eukaryotes looks almost the same as it does in prokaryotes. It also has some fundamental differences.

• Each step that generates mRNA, transcripts and rRNA is catalyzed by an enzyme called RNA-polymerase.
• Primitive mRNA is produced by transcription in eukaryotes. It consists of exons (carrying information about amino acids) and introns. To produce mature mRNA, introns are deleted. This allows for only exons that are involved in translation.