Nucleic Acids 7 Flashcards
(14 cards)
What are the 3 binding sites on a ribosome ?
- E site (exit)
- P site (peptidyl)
- A site (aminoacyl)
What do ribosomes catalyse the formation of ?
Peptide bonds
What is the size of ribosomes measured in ?
Svedbergs (S)
Sedimentation rate
What size are bacteria ribosomes ?
70S
Made of a 50S and 30S subunit
What size are eukaryote ribosomes ?
80S
Made of a 60S and 40S subunit
What do the subunits in ribosomes do ?
Small subunits- binds the mRNA being translated
Large subunits- catalyse peptide bond formation
What size are mitochondrial ribosomes ?
55S
What are the stages of translation ?
- Initiation- binding of mRNA and the first tRNA and assembly of the ribosome
- Elongation- addition of amino acids to growing peptide
- Termination- dissociation of the completed protein from the ribosome
Describe initiation translation in E.coli
- The 30S subunit binds to the ribosome binding site on the mRNA
- f-met-tRNAmet binds to the initiation codon.
- The 50S subunit binds, generating the complete ribosome
Describe initiation in eukaryotes
- The first AA is methionine not N-formyl-methionine
- The 40S subunit and Met-tRNAmet combine prior to binding to mRNA
- There is no ribosome binding site on the mRNA. Instead the 40S subunit recognises the cap at the 5’ end of the mRNA
- The 40S subunit and Met-tRNAmet migrate along the mRNA until the first AUG is reached
Describe the elongation cycle
- Binding of aminoacyl-tRNA
- Peptidyl transferase reaction- a peptide bond is synthesised
- Translocation- movement of the ribosome one codon along the mRNA
What is peptide bind formation catalysed by ?
23S rRNA
What are the elongation factors in translation ?
- EF-Tu (EF-1alpha in eukaryotes)- delivers aminoacyl tRNAs to ribosome
- EF-G (EF-2 in eukaryotes)- moves ribosome along the mRNA
What is ricin ?
An antibiotic/ inhibitor
