Steps of Transcription From DNA to RNA

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Transcription of DNA to RNA

DNA
DNA is transcribed from an RNA template. Cultura/KaPe Schmidt/Getty Images

Transcription is the name given to the chemical synthesis of RNA from a DNA template. In other words, DNA is transcribed in order to make RNA, which is then decoded to produce proteins.

Overview of Transcription

Transcription is the first stage of the expression of genes into proteins. In transcription, a mRNA (messenger RNA) intermediate is transcribed from one of the strands of the DNA molecule. The RNA is called messenger RNA because it carries the 'message' or genetic information from the DNA to the ribosomes, where the information is used to make proteins. RNA and DNA use complementary coding, where base pairs match up, similar to how the strands of DNA bind to form a double helix. One difference between DNA and RNA is that RNA uses uracil in place of the thymine used in DNA. RNA polymerase mediates the manufacture of an RNA strand that complements the DNA strand. RNA is synthesized in the 5' -> 3' direction (as seen from the growing RNA transcript). There are some proofreading mechanisms for transcription, but not as many as for DNA replication. Sometimes coding errors occur.

Steps of Transcription

Transcription may be broken into five stages: pre-initiation, initiation, promoter clearance, elongation, and termination.

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Comparison of Transcription in Prokaryotes Versus Eukaryotes

plant cell
In animal and plant cells, transcription occurs in the nucleus. Science Photo LibraryS- ANDRZEJ WOJCICKI / Getty Images

There are significant differences in the process of transcription in prokaryotes versus eukaryotes.

  • In prokaryotes (bacteria), transcription occurs in the cytoplasm. Translation of the mRNA into proteins also occurs in the cytoplasm. In eukaryotes, transcription occurs in the cell's nucleus. mRNA then moves to the cytoplasm for translation.

     

  • DNA in prokaryotes is much more accessible to RNA polymerase than DNA in eukaryotes. Eukaryotic DNA is wrapped around proteins called histones to form structures called nucleosomes. Eukaryotic DNA is packed to form chromatin. While RNA polymerase interacts directly with prokaryotic DNA, other proteins mediate the interation between RNA polymerase and DNA in eukaryotes.

     

  • mRNA produced as a result of transcription is not modified in prokaryotic cells. Eukaryotic cells modify mRNA by RNA splicing, 5' end capping, and addition of a polyA tail.
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Transcription - Pre-Initiation

Helix
Atomic Imagery / Getty Images

The first step of transcription is called pre-initiation. RNA polymerase and cofactors bind to DNA and unwind it, creating an initiation bubble. This is a space that grants RNA polymerase access to a single strand of the DNA molecule.

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Transcription - Initiation

RNAP
This diagram depicts the initiation of transcription. RNAP stands for the enzyme RNA polymerase. Forluvoft / Wikipedia Commons

The initiation of transcription in bacteria begins with the binding of RNA polymerase to the promoter in DNA. Transcription initiation is more complex in eukaryotes, where a group of proteins called transcription factors mediate the binding of RNA polymerase and the initiation of transcription.

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Transcription - Promoter Clearance

space-filling model of DNA
This is a space-filling model of DNA, the nucleic acid that stores genetic information. Ben Mills / Wikimedia Commons

RNA polymerase must clear the promoter once the first bond has been synthesized. Approximately 23 nucleotides must be synthesized before RNA polymerase loses its tendency to slip away and prematurely release the RNA transcript.

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Transcription - Elongation

transcription elongation
This diagram depicts the elongation step of transcription. Forluvoft / Wikipedia Commons

One strand of DNA serves as the template for RNA synthesis, but multiple rounds of transcription may occur so that many copies of a gene may be produced.

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Transcription - Termination

transcription termination
This is a diagram of the termination step of transcription. Forluvoft / Wikipedia Commons

Termination is the final step of transcription. Termination results in the release of the newly synthesized mRNA from the elongation complex.

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Your Citation
Helmenstine, Anne Marie, Ph.D. "Steps of Transcription From DNA to RNA." ThoughtCo, Apr. 20, 2017, thoughtco.com/steps-of-transcription-from-dna-to-rna-603895. Helmenstine, Anne Marie, Ph.D. (2017, April 20). Steps of Transcription From DNA to RNA. Retrieved from https://www.thoughtco.com/steps-of-transcription-from-dna-to-rna-603895 Helmenstine, Anne Marie, Ph.D. "Steps of Transcription From DNA to RNA." ThoughtCo. https://www.thoughtco.com/steps-of-transcription-from-dna-to-rna-603895 (accessed December 12, 2017).