Biology And Biomedical Sciences BIOL 2960 Lecture Notes - Lecture 35: Small Gtpase, Cell Membrane, Signal Recognition Particle
24 Apr 2017
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Prokaryotes: shine-delgarno sequence positions ribosomes and chooses initiator codon; formylated methionine used as the initial aa. Gtp is hydrolyzed and eifs are released, 3) initiation; no f-met in eukaryotes, just methionine -- scanning requires atp. Prokaryotes: regulated by access to the shine-delgarno sequence. Repressors cover up the sd sequence; activators make it accessible. In eukaryotes there are two types of regulation: Global regulation through inhibition of initiation factor activity. One major target is the factor that binds the 5" cap structure. Rna -- non-coding rnas are processed into mirnas. Drosha -- a nuclease releases hairpin structure in nucleus. Dicer -- a nuclease cuts off loop; releases double stranded rna in cytoplasm. Risc -- rna induced silencing complex -- chooses one of the strands and presents it to mrna for complementary base-pairing and translation repression -- represses translation. Micrornas are small single-stranded rnas (~20 bp) which are processed out of longer rna pol2 transcribed rnas (pre-mirnas) by two different processing nucleases.
