CBIO 3400 Lecture Notes - Lecture 8: Eif2, Eif2B, Start Codon
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Exam 4 Lecture 8
mRNA Translation I
Translation Cycle: Imitation & Energy Expenditures
• tRNA recognizes the start codon (methionine) and small ribosomal subunit.
• GTP hydrolysis provides the energy
• P site
• A site
• E site
o Where the used tRNA is released.
Translation Cycle: Initiation Methionine Control
• Slide 21
• Methionine is attached to initiation tRNA which binds to heterotrimer (eIF2). This
complex then binds to small ribosomal subunit.
• Helicase starts to melt RNA so this complex scan on the message looking for the 1st start
codon. Once they find the start codon, there is a liaising of this start site. The hydrolysis
says this is the start to stop. Hydrolysis allows the recruitment of the large ribosomal
subunit, so they all then come together.
• Must deal with recycling. eIFT-GDP is recycled via GEF (eIF2B) which exchanges out the
GDP with GTP so the cycle can repeat again. This is a critical point in this pathway.
o Phosphorylation occurs in EIF2 alpha
▪ Two alpha phosphorylated, and no longer able to interact with GEF
o Cellular stress triggers phosphorylation of eIF2 locking it in an inactive state,
which halts translation.
• In the presence of stress, cells put a halt to energy expenditures.
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