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Download tRNA, rRNA, and RNAi Transfer RNA (tRNA) Characteristics of tRNA
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Transcript
Transfer RNA (tRNA) tRNA, tRNA, rRNA, rRNA, and RNAi Chapter 14 continued Characteristics of tRNA tRNA: tRNA: Linking the genetic code to proteins. Figure 14.22 • Each tRNA attaches to a particular amino acid – Carries it to Ribosome • tRNA has rare Modified Bases – Made by tRNA-modifying enzymes • Secondary structure called a cloverleaf 3-D Structure Ribbon Model Flattened Cloverleaf Model Figure 14.21 The names of the arms come from the presence of modified bases. DHU: dihydrouridine TΨC: Thymine, pseudouracil, cytosine 1 Transfer RNA Gene Structure tRNA Introns • E. coli: single copies of some tRNA genes, multiples of others. • Splicing of tRNA introns different from spliceosomal introns. • Eukaryotes: Many copies of each tRNA gene • Intron cut at both ends with an endonuclease. Ribosomal RNA (rRNA) rRNA) rRNA: rRNA Building block of the ribosome Characteristics of rRNA • rRNA genes present in multiple copies • Extensive post transcriptional modification • The ribosome: – Several rRNA molecules and many proteins 2 In both Bacteria and Eukaryotes, tRNA and rRNA are modified after transcription. snoRNAs (small nucleolar RNAs) help to cleave and modify eukaryotic rRNAs into mature ribosomes. Small Interfering RNAs and MicroRNAs 3 RNAi RNAi and Fluffy • Abundant in eukaryotes • Humans have 200+ miRNA genes • May have evolved as “an immune system” for the genome • Can use RNAi to “knock down” expression of specific genes 4
