BIOL 1411 1st Edition Lecture 23Outline of Last Lecture I. DNA Replication and Function a. Repairsb. Genes Code for Proteins Outline of Current Lecture II. TranscriptionIII. Genetic CodeLecture- Initiation of Transcriptiono Initiation requires a promoter- a special sequence of DNAo RNA polymerase binds to the promotero Promoter directs RNA polymerase where to start and which direction to transcribeo Part of each promoter is the initiation site of transcription o DNA is transcribed to from RNA- Transcription of DNA to RNAo Elongation: RNA polymerase unwinds DNA about 10 base pairs at a time; reads template in 3’ 5’ directiono The RNA transcript is antiparallel to the template DNA strand; nucleotides added at 3’ endo 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 template- for others a helper protein pulls it away- Introns and Exonso Eukaryotic genes may have noncoding sequences- intronso Introns appear in the primary mRNA transcript- pre-mRNA; introns are removed from the pre-mRNA in the nucleuso The coding sequences are contained in the exons that remaino 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 splicingo RNA splicing removes introns and splices exons togethero Newly transcribed pre-mRNA is bound at ends by snRNPs –small nuclear ribonucleoprotein particleso 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-mRNAo G cap- is added to the 5’ endo Poly A tail added at 3’ end AAUAA sequence after last codon is signal for an enzyme to cut the pre-mRNA; then another enzyme adds 100 to 300 adenines- the “tail” May assist in export from nucleus; important for stability of mRNA - Genetic Codeo The genetic code: specifies which amino acids will be used to buld a polypeptideo Codon: a sequence of 3 bases- each codon specifies a particular amino acid, or stops translationo Start Codon: AUG- initiation signal for translation near 5’ end of mRNA. Specifies methionine and establishes 3-base reading frameo Stop codons: UAA, UAG, UGA- stop translation and polypeptide is released o Nearly
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