Transcription produces RNA strands from DNA in cells, with eukaryotes doing so in the nucleus and prokaryotes in the cytoplasm. RNA polymerases control the process, using a promoter to uncoil DNA and create a new RNA strand. The RNA nucleotides correspond to DNA nucleotides, with RNA containing uracil instead of thymine. The process ends when the RNA polymerase detaches from the DNA molecule.
The transcription process occurs within all cells and results in the production of RNA strands. The DNA inside the cell provides the transcript, or blueprint, that determines the sequence of nucleotides that come together to form RNA. Depending on the cell type, transcription occurs in the nucleus or in the cytoplasm. Within eukaryotes – cells that contain membrane-bound organelles – transcription occurs in the nucleus. In prokaryotes – cells that do not contain organelles – the process takes place in the cytoplasm.
The genes found along the DNA strands within the cell provide the code for the different proteins the cell makes. There are two stages in protein formation, which are the transcription process and the translation of the RNA that is produced. Messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA) are the three types of RNA that can be produced. All three are required to make proteins within the cytoplasm.
There are several distinct steps involved in the transcription process, which are controlled by enzymes called RNA polymerases. To initiate the transcription process, RNA polymerase binds to the DNA molecule in a specific region called the promoter. This region is located along the DNA strand before the place where the gene will be transcribed. When RNA polymerase attaches to the promoter region, it causes double-stranded DNA to uncoil and decompose so that it can move along a single strand of the molecule.
The single strand of DNA is used as a template for the sequence of RNA nucleotides that will be joined to form the new strand of RNA. For every DNA nucleotide, there is a corresponding RNA nucleotide that joins together to make the RNA molecule, and both DNA and RNA contain four nucleotides. Guanine, cytosine and adenine are found in both DNA and RNA. Thymine is only found in DNA; RNA contains uracil instead of thymine.
As RNA polymerase moves along the DNA strand, it attacks a guanine if it encounters a cytosine and vice versa. When a thymine occurs within the DNA strand, an adenine is added to the RNA chain. Finally, when the DNA strand has an adenine nucleotide, the corresponding RNA nucleotide is a uracil. Each of the complementary nucleotides is linked to the previous ones in the chain until it reaches the final termination code on the DNA strand. At this point, the RNA polymerase detaches from the DNA molecule and the new strand of RNA is released.
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