eukaryotic 80s ribosome and tRNA
- Created by: natasha8sherry
- Created on: 11-01-14 11:34
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- Eukaryotic 80S ribosome and transfer RNA
- Prokaryotic ribosome
- 70S - made of 50S + 30S
- cotranscriptional translation
- Eukaryotic ribosome
- 80S - made of 60S + 40S
- transcription and translation separated physically and temporally
- ribosomes made of 65% rRNA and 35% ribosomal protein
- small ribosomal subunit
- decoding centre required for reading the mRNA genetic code
- large subunit
- contains peptidyltransferase centre where AA are added onto the nascent polypeptide
- small ribosomal subunit
- multiple ribosomes loaded onto an actively translating mRNA = polysome
- tRNA
- acts as molecular adaptor that associates and mRNA codon to a specific AA
- more than one tRNA associates with a particular AA
- fold into a series of 4 base-paired stems which adopt an L shape (although they are drawn with a cloverleaf structure)
- the anticodon loop is a single-stranded area which contains the anticodon that hybridises to a corresponding 3 base codon on the mRNA
- the 5' and 3' ends of the tRNA base pair together to form the acceptor stem where the AA is added
- the 3' end terminates in the residues CCA which becomes charged when the relevant AA when it is transferred by aminoacyl tRNA synthetase
- added complexity in tRNA structure arises from base modifications
- this changes specific bases to generate inosine, pseudouridine, dihydrouridine and ribothymidine
- if a modified base is in the anticodon, the base pairing specificity canchange, resulting in a phenomenon called wobble
- this is where the first 2 anticodon bases follow standard base pairing, but the 3rd base affords a large degree of flexibility
- e.g. a U on mRNA can be recognised by A, G or I
- the consequence is ththe consequenece is that a given codon can be reocgnised by multiple tRNAs, which ensures the process is more efficient
- mutations affecting the 3rd base do not normally have a phenotypic effect because they do not alter the AA sequence
- this is where the first 2 anticodon bases follow standard base pairing, but the 3rd base affords a large degree of flexibility
- Prokaryotic ribosome
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