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BIOL 205 (111)


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BIOL 205
Ian D Chin- Sang

Hox proteins repress appendage formation in the abdomen Expression of gene distal-less (Dll) marks the start of development of appendages Homeotic genes controlled primarybymaternalside Abdominalsections Thoracic segments **proteindiffuses not mRNA DII (blue) repressed in A1-A8 none in A1 to A8 Hox proteins repress appendage formation in the abdomen Dllrepressed by Ultrabithorax Slippage:DIST expressed in A1 (Ubx) andAb-A Tells us that abdominalA keeps D UbxAb-Adble out ofabdominalregion mutant- Dll expressionin A1-A7 Hox proteins and segment-polarity proteins control appendage location Onlyanterior portionofsegement expressed DIST - controllinga compartment w/ina segment Hox proteins and segment-polarity proteins control appendage location Posterior instead of anterior Protein and RNA molecules compose the two subunits of a ribosome Manydifferent points to ensure translationdone withdifelity Sedementationvalues not weights RNA polI RNA polII Situate tRNAin site Cytoplasmic protein or targeted for particular membrane Prokaryotic Initiation • IF3 Antiassociation factor ◦ binds 30S subunit and promotes dissociation of 70s ribosome ◦ controls ability of 30s subunit to bind mRNA • IF2 ◦ binds and facilitats hydrolysis of GTP ◦ recognizes fMet tRNA ▪ brings to Peptidyl (P) site on ribosome ▪ all other tRNAs enter Acceptor (A) site • IF1 ◦ blocks tRNAfrom binding small subunit (futureAsite) Prokaryotic Initiation complex forms on Shine-Dalgarno Sequence of the mRNA Unique for prokaryotes - mRNAinteracts with 16S rRNAto position AUG properly Translation initiation in prokaryotes - IF3:binds 30S–anti-association - Blocks 50S & charged tRNAs - IF1 prevents tRNAs frombindingtoAsite - IF2:a GTPase binds 30S, IF1 & fmet tRNAfmet positions on AUG ofmRNAinthe P (peptidyl)site → codon-anticodon(tRNAcontains ainticodon) interaction– 30S → conformationchange releases IF3 - co50S subunit canrebind - stimulates GTPase activityofIF2 - initiationfactors released Steps in translation elongation - Ef-Tu-GTP-amino acyltRNAbrought toAsite - and cycle offONLY if: Ef-Tubinds to tRNA3’ - correct codon-anticodonmatch→ GTPase activated by end-masks coupled aa 50S subunit ‘factor bindingcenter’ Ef-Tuis a GTPase - same center that activates IF2 GTPase di-acelated Requires EF-G whichrequires GTP Ef-Tuexits – recharged byEf-Ts
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