{"id":4457,"date":"2017-02-13T16:31:07","date_gmt":"2017-02-13T16:31:07","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology1\/?page_id=4457"},"modified":"2017-02-13T21:12:50","modified_gmt":"2017-02-13T21:12:50","slug":"dna-rna-proteins","status":"publish","type":"page","link":"https:\/\/courses.lumenlearning.com\/ivytech-wmopen-nmbiology\/dna-rna-proteins\/","title":{"rendered":"DNA \u2192 RNA \u2192 Proteins"},"content":{"rendered":"

The central dogma of life can be defined in a fairly simple way: DNA makes\u00a0RNA, which in turn makes proteins:<\/p>\n

\"DNA<\/p>\n

In transcription, your genetic code is transcribed, or written, into RNA. In translation, this RNA is then translated into proteins. Of course, the processes of transcription and translation are a little more complicated than that.\u00a0Let’s review the two processes:<\/p>\n

Transcription: DNA \u2192 RNA<\/h2>\n

Transcription is the first half of the Central Dogma. This is where DNA is translated into RNA. Transcription occurs in the nucleus of the cell\u2014DNA cannot leave the nucleus. There are three steps in transcription: initiation, elongation, and termination (these are also the same steps as in translation; however, different things happen in the steps of the different processes).<\/p>\n

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  1. Initiation:<\/strong>\u00a0Transcription begins at a\u00a0promoter: a specific region of a gene. RNA polymerase binds to the promoter. This signals the DNA to unwind. The enzyme is now ready to make mRNA<\/li>\n
  2. Elongation: <\/strong>Nucleotides are added to the mRNA strand\n
      \n
    • Remember: thymine only occurs in DNA, and uracil only occurs in RNA!<\/li>\n<\/ul>\n<\/li>\n
    • Termination:\u00a0<\/strong>Transcription ends when RNA polymerase encounters a stop (termination) sequence in the gene.<\/li>\n<\/ol>\n

      RNA Polymerase<\/h3>\n

      There are three types of eukaryotic RNA Polymerase. Fittingly, they’re named\u00a0RNA Polymerase I,\u00a0RNA Polymerase II, and\u00a0RNA Polymerase III.<\/p>\n

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      • RNA polymerase I<\/b> is located in the nucleolus, and facilitates the\u00a0transcription of ribosomal RNA (rRNA), which is then processed and assembled into ribosomes.<\/li>\n
      • RNA polymerase II<\/b> is located in the nucleus and synthesizes all protein-coding nuclear pre-mRNAs.<\/li>\n
      • RNA polymerase III<\/b> is also located in the nucleus. This polymerase transcribes a variety of structural RNAs that includes the 5S pre-rRNA, transfer pre-RNAs (pre-tRNAs), and small nuclear pre-RNAs.<\/li>\n<\/ul>\n

        mRNA Processing<\/h3>\n

        After transcription, eukaryotic pre-mRNAs must undergo several processing steps before they can be translated.<\/p>\n

        Pre-mRNAs are first coated in RNA-stabilizing proteins; these protect the pre-mRNA from degradation while it is processed and exported out of the nucleus. The three most important steps of pre-mRNA processing are the addition of stabilizing and signaling factors at the 5\u2032 and 3\u2032 ends of the molecule, and the removal of intervening sequences that do not specify the appropriate amino acids. In rare cases, the mRNA transcript can be \u201cedited\u201d after it is transcribed.<\/p>\n

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        PRactice Questions<\/h3>\n

        In which step of transcription does\u00a0the DNA unwind?<\/p>\n