ch369_ch 19-transcription

ch369_ch 19-transcription - Vocabulary Prokaryotes. The...

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Vocabulary Prokaryotes . The single-cell organisms that lack a cell nucleus. The prokaryotes include the bacteria and archaea , which are actually separate branches on the tree of life. Eukaryotes . Organisms with cells that have nuclei. yeast. An example of a bacterial cell from Wikipedia.
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“Transcription and RNA” - Chapter 19 Replication: DNA ============> copied DNA Transcription: DNA ============> mRNA, rRNA, tRNA, other RNA Translation: mRNA ==============> protein DNA polymerase Ribosome RNA polymerase
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In transcription , an enzyme (RNA pol) makes an RNA complementary to the bottom DNA strand (so the new RNA has the same sequence as the DNA top strand, except with U instead of T). Transcription: DNA =============> RNA RNA polymerase Example of transcription:
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Not all of an organism’s DNA is transcribed into RNA. “gene” = section of a DNA sequence that is transcribed into RNA by RNA pol. Only a fraction of the human DNA genome is transcribed into RNA. (in human genome, maybe 25% of DNA is transcribed to RNA) RNAs that are transcribed include: mRNA (messenger RNA) - codes for protein tRNA (transfer RNA) - delivers amino acids to ribosome in protein synthesis rRNA (ribosomal RNA) - component of the ribosome miRNA (micro RNA) - involved in regulation of gene expression.
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Bacterial mRNA - In bacteria, things are relatively simple: RNA polymerase makes mRNA, which is translated to protein.
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mRNA production in eukaryotes is more complicated. transcription Transcription, splicing and capping all happen in the cell nucleus, mature mRNA is exported to cytosol.
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In eukayotes, pre-mRNA is “spliced” by the “spliceosome” to remove “introns”. Exons are the protein-coding segments of mRNA. Introns are the part of pre-mRNA that needs to be removed before it becomes a mature mRNA that encodes protein. A typical human mRNA may have 10 exons of 150 nt each, separated by 9 introns of 3000 nt each ! Bacterial mRNA does not contain introns. Most eukaryotic pre-mRNA does contain introns. Nearly all human pre-mRNA contains introns. RNA splicing ” refers to the process of removing introns from pre-mRNA to make mature mRNA that can be translated into protein by the ribosome.
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Introns are removed by a complex apparatus called the spliceosome . The spliceosome is a complex apparatus within the cell nucleus that contains several large RNAs and dozens of protein components . (the spliceosome RNAs are called the U1, U2, U4, U5, U6 RNAs).
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ch369_ch 19-transcription - Vocabulary Prokaryotes. The...

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