Intervening DNA sequences that are transcribed and then removed from the final mRNA
The central dogma of life can be defined in a fairly simple way: DNA makes RNA, which in turn makes proteins: Show
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. Let’s review the two processes: Transcription: DNA → RNATranscription is the first half of the Central Dogma. This is where DNA is translated into RNA. Transcription occurs in the nucleus of the cell—DNA 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).
RNA PolymeraseThere are three types of eukaryotic RNA Polymerase. Fittingly, they’re named RNA Polymerase I, RNA Polymerase II, and RNA Polymerase III.
mRNA ProcessingAfter transcription, eukaryotic pre-mRNAs must undergo several processing steps before they can be translated. 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′ and 3′ 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 “edited” after it is transcribed. PRactice QuestionsIn which step of transcription does the DNA unwind? Which is a function of RNA polymerase II?
Translation: RNA → proteinTranslation occurs in the cytoplasm. There are three steps in translation: initiation, elongation, and termination (these are also the same steps as in transcription; however, different things happen in the steps of the different processes).
Ribosomes and tRNAsIn addition to the mRNA template, many molecules and macromolecules contribute to the process of translation.
CodonsThe amino acids that make up proteins are encoded by a nucleotide triplet codon: for example, the protein serine is encoded by the codons UCU, UCC, UCA, and UCG. The reading frame for translation is set by the AUG start codon near the 5′ end of the mRNA. The three “nonsense codons,” UAA, UAG, and UGA indicate that translation should be terminated. Practice QuestionsWhich macromolecule binds to the mRNA template to aid in translation?
What do nucleotide triplet codons encode? What is removed from mRNA after transcription?Most pre-mRNA molecules have sections that are removed from the molecule, called introns, and sections that are linked or together to make the final mRNA, called exons. This process is called splicing.
What is an intervening sequence of nucleotides that will be removed during mRNA processing?Introns are nucleotide sequences in DNA and RNA that do not directly code for proteins, and are removed during the precursor messenger RNA (pre-mRNA) stage of maturation of mRNA by RNA splicing.
What are intervening sequences on mRNA that are transcribed but not translated called?The introns are the non-coding intervening sequences that lie between the exons of a cistron of a gene. The introns are transcribed onto the primary RNA transcript (hnRNA) but are removed by splicing during the post-transcriptional processing of the hnRNA to form functional mRNA.
What is an intervening sequence of DNA that is not expressed called?These are expressed in the mature and processed RNA. But the sequence which does not appear in processed and mature RNA is called an intron sequence. These are the intervening sequences in between the exons.
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