BIOL 1411 1st Edition Lecture 23 Outline of Last Lecture I DNA Replication and Function a Repairs b Genes Code for Proteins Outline of Current Lecture II Transcription III Genetic Code Lecture Initiation of Transcription o Initiation requires a promoter a special sequence of DNA o RNA polymerase binds to the promoter o Promoter directs RNA polymerase where to start and which direction to transcribe o Part of each promoter is the initiation site of transcription o DNA is transcribed to from RNA Transcription of DNA to RNA o Elongation RNA polymerase unwinds DNA about 10 base pairs at a time reads template in 3 5 direction o The RNA transcript is antiparallel to the template DNA strand nucleotides added at 3 end o RNA polymerases do not proofread and correct mistakes Termination is specified by a base sequence in DNA that destabilizes the transcription complex For some genes the transcript falls away from the RNA polymerase and DNA templatefor others a helper protein pulls it away Introns and Exons o Eukaryotic genes may have noncoding sequences introns o Introns appear in the primary mRNA transcript pre mRNA introns are removed from the pre mRNA in the nucleus o The coding sequences are contained in the exons that remain o The processed mRNA is exported rom the nucleus to the cytoplasm o The spliceosome cuts pre mRNA releases introns and splices exons together to produce mature mRNA These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute RNA splicing o RNA splicing removes introns and splices exons together o Newly transcribed pre mRNA is bound at ends by snRNPs small nuclear ribonucleoprotein particles o Consensus sequences are short sequences at exon intron junctions SnRNPs bind here And also near the 3 end other the intron o In the eukaryotic nucleus and in addition to intron removal pre mRNA is modified at both ends Processing the ends of eukaryotic pre mRNA o G cap is added to the 5 end o Poly A tail added at 3 end AAUAA sequence after last codon is signal for an enzyme to cut the premRNA then another enzyme adds 100 to 300 adenines the tail May assist in export from nucleus important for stability of mRNA Genetic Code o The genetic code specifies which amino acids will be used to buld a polypeptide o Codon a sequence of 3 bases each codon specifies a particular amino acid or stops translation o Start Codon AUG initiation signal for translation near 5 end of mRNA Specifies methionine and establishes 3 base reading frame o Stop codons UAA UAG UGA stop translation and polypeptide is released o Nearly universal
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