BIS2A M2 Lecture 19

Eukaryotic transcription occurs in the ____, translation occurs in the ___-

nucleus — translation

What are the 4 steps of translation initiation in eukaryotes?

1. Load small subunit with tRNAi-Met directly into P site

2. Initiation factors bound to mRNA’s 5’cap and 3’polyA tail recruit the small subunit to the mRNAa

3. Scan for start codon embedded in Kozak sequence

4. Recruit large subunit

What recruitment sequence brings the small subunit of ribosome to the mRNA in eukaryotes?

Kozak

Explain the role of the 5’cap in eukaryotic translation. Why don’t eukaryotes use polycistronic transcripts?

5’cap recruits and positions the small subunit, allowing translation to occur. Bc eukaryotes need the 5’end cap to recognize mRNA, they don’t use polycistronic transcripts

The end of encoded protein is signaled by ___ ______ What recognizes them? What can’t recognize them?

stop codons. They can’t be recognized by any tRNAs and instead are recognizes by release factors.

Explain how translation termination occurs in eukaryotes.

As the ribosome complex moves along mRNA and reaches a stop codon, there are no tRNAs that can recognize this codon. Instead, a release factor will bind to the A site, pushing the last tRNA from the P site to the E site (this will release a GTP molecule in the process). Then, the release factor will promote the catalysis of H2O which will break the bond between the last amino acid and the last tRNA. Then everything dissociates - the subunits separate, the tRNA and peptide chain separate, and the ribosome complex separates from the mRNA.