BIOL 142 Lecture Notes - Lecture 3: Meiosis, Release Factor, Ploidy
Tuesday, January 30, 2018
BIOL 142
•Template strand (anti-sense strand): 3’ - 5’ direction, promoter"
•Promoter - initiates transcription"
•Promoter does not get transcribed, terminator does - because it is used to make the
hairpin at the end"
•Transcription Start Site - +1 base point"
•mRNA processing"
•Splicing: non-coding sequences (introns) are removed and coding sequences
(exons) are joined together"
•Chemical modifications - primary RNA transcript are also processed by the
addition of a 5’ cap (guanine) and a poly(A) tail - provides extra stability"
•Translation"
•The sequences of bases in the mRNA is converted to an aa sequence"
•Ribosomes catalyze translation of the mRNA sequence into protein"
•Prokaryotes - simultaneous translation and transcription events"
•Eukaryotes - transcription and translation separated"
•tRNA:"
•The CCA (ser) sequence at the 3’ end of each tRNA is the binding site for amino
acids the triplet on the loop at the opposite end is the anticodon that base-pairs
with the mRNA codon"
•All of the tRNAs in a cell have the same structure, shaped like an upside down L"
•They vary at the anticodon and the attached amino acid"
•There are 61 different codons - but only about 40 tRNAs in most cells"
•To resolve this deficit, Wobble hypothesis"
•Wobble hypothesis proposes"
•The anticodon of tRNAs can bind successfully"
•To a codon whose third position"
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