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RNA strand is almost immediately detached from the DNA as it is being synthesised, a large number of RNA copies can be produced from a single gene in a relatively short amount of time. The synthesis of additional RNA molecules can begin before the first RNA is finished being produced, which allows for this to happen. When RNA polymerase molecules proceed in this manner, each moving at a speed of approximately 20 nucleotides per second (the speed in eukaryotes), over a thousand transcripts can be synthesised in an hour from a single gene. This is accomplished when RNA polymerase molecules follow closely on each other’s heels.
Principal ideas
The process of copying (or “transcription”) the DNA sequence of a gene in order to produce an RNA molecule is referred to as transcription.
The primary enzyme responsible for transcription is called RNA polymerase.
When RNA polymerase binds to a promoter sequence in the region close to the beginning of a gene, transcription of the gene starts (directly or through helper proteins).
When making a new molecule of complementary RNA, RNA polymerase follows the pattern of one of the DNA strands, which is referred to as the template strand.
The process that marks the end of transcription is known as termination. The sequences in the RNA that signal that the transcript is complete are what determine when the process will end.
From DNA to RNA and beyond
The genetic instructions that are contained in a cell’s genes can only be read out, or expressed, through the processes of transcription and translation. Cells are able to rapidly produce a large quantity of protein when it is necessary to do so due to the fact that a single gene can produce a large number of copies of identical RNA, and each RNA molecule can direct the synthesis of a large number of identical protein molecules. However, the transcription and translation of each gene can take place with varying degrees of efficiency, enabling the cell to produce vast quantities of some proteins while producing only trace amounts of others. In addition, as we will see in the following chapter, a cell is able to alter (or regulate) the expression of each of its genes in response to the requirements of the current environment, most obviously through the regulation of the production of its RNA.
Resulting in the Production of RNA that Is Complementary to One Strand of DNA
DNA transcription, a process that has certain parallels to the process of DNA replication, which was covered in Chapter 5, is responsible for the production of all of the RNA found in a cell. The first step in transcription involves opening up and unwinding a small section of the DNA double helix in order to reveal the bases that are located on each strand of DNA. After this, one of the two strands of the DNA double helix is used as a template to guide the production of an RNA molecule by the cell. The complementary base-pairing that occurs between incoming nucleotides and the DNA template is what determines, in the same way that it does in DNA replication, the nucleotide sequence of the RNA chain. In a reaction that is catalysed by enzymes, the incoming ribonucleotide is covalently linked to the growing RNA chain when there is a good match. Therefore, the RNA chain that is produced by transcription is known as the transcript, and it has a nucleotide sequence that is exactly complementary to the strand of DNA that was used as the template. This occurs because the RNA chain is lengthened one nucleotide at a time.
Conclusion
A representation in schematic form of the subnuclear structures. Cajal bodies are thought to be the locations in a typical vertebrate nucleus where snRNPs and snRNPs undergo their final modifications. A typical vertebrate nucleus has several Cajal bodies. It is hypothesised that the interchromatin granule clusters serve as storage sites.
