Translation part 2 Flashcards
Describe the formation of the prokaryotic initiation complex
In step 1, GTP, IF1, IF2, and IF3 bind to the 30S ribosomal subunit.
In step 2, the mRNA and fMet–tRNAiMet bind to the complex with the Shine–Dalgarno sequence of mRNA aligning with complementary sequences in the 16S rRNA in the 30S ribosomal subunit,
and IF3 is released.
In step 3, hydrolysis of GTP facilitates binding of the 50S ribosomal subunit,
with the release of IF1 and IF2 to form the functional 70S ribosomal initiation complex.
What happens in the elongation phase
The 6-step elongation cycle requires the hydrolysis of 2 GTP, one to promote binding of the AA– tRNAAA to the A site, and one to facilitate translocation
of the ribosome in the 3’ direction.
Describe the exit of the new polypeptide from the ribosome
The newly-synthesized polypeptide exits through a hydrophobic tunnel in the 50S subunit at the site of peptide bond formation.
What happens in the termination phase
Release factors (RFs) bind to the termination/stop codon(s) and lead to release of the polypeptide chain.
Initiation of translation in eukaryotes
eukaryotic translation initiation complexes include the lack of a specific ribosome binding site in the
mRNA in eukaryotes and a greater number of eukaryotic initiation factors (eIFs) required.
Assembly of the eukaryotic translation initiation complex
Binding: The 40S ribosomal subunit binds nonspecifically to mRNA and scans 5’ to 3’ for the AUG start codon.
Formation of 43S Complex: A ternary complex (GTP-eIF2 + Met-tRNAiMet) binds to the 40S ribosomal subunit, forming the 43S pre-initiation complex with eIF3, eIF5, and eIF1A.
Assembly of 48S Complex: eIF3 interacts with the eIF4G subunit of the 5’ cap-binding complex on mRNA, forming the 48S pre-initiation complex, which includes eIF4E, eIF4A, and an RNA helicase.
mRNA Loop Formation: The 48S complex forms a looped mRNA structure, aiding ribosomal scanning for the AUG codon.
Formation of 80S Complex: Addition of eIF5B-GTP and the 60S ribosomal subunit triggers GTP hydrolysis, forming the functional 80S ribosome and starting polypeptide synthesis.
What are the 4 examples of antibiotics that inhibit bacterial protein synthesis
Does not effect eukaryotes
Chloramphenicol: Binds to the 50s subunits and prevents peptide bond formation
Erythromycin: Binds to the 50s subunit and prevents translocation
Tetracyclines: Prevents tRNA binding to the A site in the ribosome
Streptomycin: Alters the structure of the 30s subunit, causing errors in translation
