DNA Transcription: Process, Elements, and Stages

Elements Involved

In order to perform the transcription of DNA into cells, the following elements are required:

• Original DNA to serve as a template to be copied.
• RNA polymerase: synthesizes RNA from a DNA template.
• Ribonucleotide triphosphates to perform the copy.
• Poly-A polymerase, small nuclear ribonucleoprotein, RNA ligase.

Transcription Mechanism

As in replication, there are differences between prokaryotes and eukaryotes. The main differences are the existence of multiple RNA polymerases in eukaryotes and, above all, the need to produce a "mature" form of some RNAs due to the existence of introns. The process is divided into three stages:

• Initiation: The RNA polymerase binds to a region of DNA prior to the DNA that is to be transcribed. It then unwinds the DNA strand and separates the two strands, starting the process of transcribing the DNA copy. This copy requires no primer. The ribonucleotides are added in the 5'-3' direction. For the transcription of a gene encoding a protein, RNA polymerase binds to a control area called the PROMOTER, which regulates the activity of RNA polymerase and thus regulates gene expression.
• Elongation: The RNA polymerase continues to add ribonucleotides complementary to the DNA until it reaches a certain sequence that signals the end of the area to be transcribed. When about 30 ribonucleotides have already been added at the 3' end, they are joined by a modified nucleotide, 7-methyl guanosine, forming what is called the "cap", or the end "Cap".
• Termination: The transcript ends, and the newly formed RNA is added to a queue of about 200 adenine nucleotides, the poly-A tail, added by the enzyme poly-A polymerase, which helps prevent the RNA from being destroyed by cellular nucleases.
• Maturation of transcription products: This occurs in the nucleus of eukaryotic cells and is performed by small nuclear ribonucleoproteins (snRNPs) by removing intron RNA and leaving the exons free to be bound by an RNA ligase.

After these processes, an RNA (messenger, transfer, ribosomal, or nucleolar) is formed, which will then move to where it carries out its function, usually in the cytoplasm.