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Lecture 8

CBIO 3400 Lecture Notes - Lecture 8: Eif2, Eif2B, Start Codon

Cellular Biology
Course Code
CBIO 3400

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CBIO 3400
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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