Subtopic 3.2: RNA Transcription
RNA Transcription is the process whereby a particular segment of DNA is transcripted into an equivalent RNA sequence
The transcription starts with binding of the enzyme RNA polymerase to a promoter sequence on the DNA, a regulatory region that dictate where the transcription should start. The DNA is transcribed from 3′ to 5′ and occurs only on one of the DNA strands, the template strand . The enzyme RNA polymerase travels down the DNA from 3′ to 5′ while matching the appropriate RNA to its DNA counterpart, utilizing uracil matched with adenine instead of thymine. As in DNA replication, energy for the formation of the phosphodiester bond is derived from hydrolysis of the two terminal phosphate bonds of the nucleoside triphosphate. Multiple RNA polymerases can transcribe on a single DNA gene sequence, allowing rapid production of the RNA product.
- mRNA: for genes that codes for a protein.
- tRNA: for a transfer RNA.
- rRNA: for assembly of a ribosome.
- miRNA: (micro RNA) which binds to mRNA and inhibits its translation
- siRNA: (small-interfering RNA) which binds to mRNA and aids in its degradation.
- snRNA: (small nuclear RNA) which participates in RNA processing as part of the spliceosomes.
- snoRNA: (small nucleolar RNA) which participate in nucleolar RNA processing.
The transcription starts with binding of the enzyme RNA polymerase to a promoter sequence on the DNA, a regulatory region that dictate where the transcription should start. The DNA is transcribed from 3′ to 5′ and occurs only on one of the DNA strands, the template strand . The enzyme RNA polymerase travels down the DNA from 3′ to 5′ while matching the appropriate RNA to its DNA counterpart, utilizing uracil matched with adenine instead of thymine. As in DNA replication, energy for the formation of the phosphodiester bond is derived from hydrolysis of the two terminal phosphate bonds of the nucleoside triphosphate. Multiple RNA polymerases can transcribe on a single DNA gene sequence, allowing rapid production of the RNA product.
Figure 2. Machinery of RNA transcription
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Promoter region: are specific DNA sequences, usually located upstream and near the transcription start sites of genes and serves as a binding site for proteins called transcription factors that recruit RNA polymerase. Example: TATA box, CpG island.
Transcription factors (TFs): include a wide number of proteins, excluding RNA polymerase, that promotes (as an activator), or blocks (as a repressor) the recruitment of RNA polymerase to DNA. TFs bind to promoter regions of DNA.
Enhancer is a short region of DNA that can be bound by transcription factors to increase or facilitate the transcription of a particular gene. They can be located up away from the gene, upstream or downstream from the start site.
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