A transcription summary is basically a fundamental process in molecular biology that plays a pivotal role in the flow of genetic information within living cells. It is the first step in the central dogma of molecular biology, where the information encoded in DNA is transcribed into a complementary RNA molecule. This process, carried out by the enzyme RNA polymerase, is a critical link between the genetic code stored in the cell’s DNA and the synthesis of functional RNA molecules, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Transcription not only enables the translation of genetic information into proteins but also serves various regulatory functions, allowing cells to control when and how specific genes are expressed. In this exploration of transcription, we will delve into its mechanisms, significance, and its role in the intricate world of genetic regulation and cellular function.

Transcription Summary

The first step is the conversion of the information into messenger RNA (mRNA).

Transcription is carried out by RNA polymerase. As with DNA synthesis, the RNA strand is made in the 5′ to 3′ direction.

Firstly, only a comparatively short molecule is produced, and secondly, only one of the DNA strands is transcribed. Since only a single strand is made, it can be produced continuously using a single enzyme; there is no need for lagging strand synthesis.

In addition the production of relatively short single-stranded RNA causes fewer topological problems: the enzyme and the RNA product can essentially rotate around the helix, so there is no need for the helicases and topoisomerases that are essential for replication.

Furthermore, RNA polymerase can start synthesis from scratch – no primer is needed. Transcription is therefore considerably simpler than replication.

In E. coli, depending on growth conditions, 2000–5000 copies of RNA polymerase may be engaged on mRNA synthesis at any time.

The transcription reaction can be divided into the three stages: initiation, in which the promoter is recognized, a bubble is created, and RNA synthesis begins; elongation, in which the bubble moves along the DNA as the RNA transcript is synthesized; and termination, in which the RNA transcript is released and the bubble closes.

Initiation

Initiation itself can be divided into multiple steps.

Template recognition begins with the binding of RNA polymerase to the double-stranded DNA at a DNA sequence called the promoter. The enzyme first forms a closed complex in which the DNA remains double-stranded. Next the enzyme locally unwinds the section of promoter DNA that includes the transcription start site to form the open complex.

Separation of the DNA double strands makes the template strand available for base pairing with incoming ribonucleotides and synthesis of the first nucleotide bonds in RNA. The initiation phase can be protracted by the occurrence of abortive events, in which the enzyme makes short transcripts, typically shorter than around 10 nucleotides (nt), while still bound at the promoter. The enzyme often makes successive rounds of abortive transcripts by releasing them and starting RNA synthesis again. The initiation phase ends when the enzyme finally succeeds in extending the chain and clearing the promoter.

Elongation

Elongation involves processive movement of the enzyme by disruption of base pairing in double-stranded DNA, exposing the template strand for nucleotide addition and translocation of the transcription bubble downstream. As the enzyme moves, the template strand of the transiently unwound region is paired with the nascent RNA at the point of growth. Nucleotides are added covalently to the 3 ‘ end of the growing RNA chain, forming an RNA-DNA hybrid within the unwound region . Behind the unwound region, the DNA template strand pairs with its original partner to reform the double helix, and the growing strand of RNA emerges from the enzyme.

The traditional view of elongation as a monotonic process, in which the enzyme moves forward along the DNA at a steady pace corresponding to nucleotide addition, has been revised in recent years. RNA polymerase pauses or even arrests at certain sequences. Displacement of the 3 ‘ end of the RNA from the active site can cause the polymerase to “backtrack” and remove a few nucleotides from the growing RNA chain before restarting. Pausing can also be programmed to occur by the use of a coded RNA hairpin structure or sequence context-caused misalignment of the incoming nucleotide with its complementary base.

Read more about Replication and Division of Nuclei and Cells

Termination

Termination involves recognition of sequences that signal the enzyme to halt further nucleotide addition to the RNA chain. In addition, long pauses can lead to termination. The transcription bubble collapses as the RNA-DNA hybrid is disrupted and the DNA reforms a duplex, phosphodiester bond formation ceases, and the transcription complex dissociates into its component parts: RNA polymerase, DNA, and RNA transcript. The sequence of DNA that directs the end of transcription is called the terminator.

Frequently Asked Questions

What is meant by transcription?

It is the process by which the nucleotide sequence present in the gene is copied in the form of nucleotide sequence of the mRNA. This mRNA then dictates the sequence of amino acids during protein synthesis.

How does transcription begin?

Transcription begins when the RNA polymerase binds the DNA at a specific sequence of nucleotides called the promoter. Later, the DNA strands are separated and the synthesis of mRNA begins.

What is the direction of transcription?

During the process of translation, mRNA is synthesized in the 5’ to 3’ direction while the DNA strand is read in the 3’ to 5’ direction.

Which enzyme plays a key role in transcription?

RNA polymerase is the main enzyme involved in the process of transcription.