4 Transcription Basics cont’d Directionality: read 3’-5’; made 5’-3’Promoter & TATA boxesNucleoside triphosphatesContains the sense strand and antisense strandSense strand = always 5’-3’ and is the same as the mRNA that is produced except T for UAntisense strand = always 3’-5’ and is the strand that forms the template and is transcribed.
8 The Genetic Code cont’d It’s a triplet code (codon) = 3 bases code for 1 amino acidThere are 64 different codonsDuplication = degeneracy = possible for 2 or more codons to code for the same amino acidCode is essential universal (find me 2 exceptions by next class for 1 point e.c. each)
10 tRNA All tRNAs have base-paired ds sections that become loops Triplet bases complementary to mRNA codons…called anticodonsA 3’-5’ CCA terminal end for amino acid attachmentThe above permit 3 distinct binding attachment of the tRNA to the ribosome
12 tRNA a S = F exampleThe base sequence of tRNa molecules vary = some variable features in its structureAn extra small loop is sometimes presentThe bp sections are sometimes helicalResults in:A distinctive 3-d shapeDistinctive chemical propertiesALLOWS THE CORRECT AA TO BE ATTACHED TO THE 3’ END BY A tRNA ACTIVATING ENZYME (aminoacyl-tRNA sythetase)There are 20 different tRNA activating enzymes – one for each of the 20 diff. AA
13 Ribosome Basics Composed of protein and rRNA Consist of 2 subunits (small and large)Possess 3 binding sites for tRNA (2 tRNAs can bind at the same time)Possess a binding site for mRNAFree vs. Bound (RER)80S in Euks vs. 70S in Proks & Euk. organelles
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