The Process: Translation-Molecular Biology

Final

What are the three major phases of translation?

initiation, elongation, and termination

What is the initiator tRNA in bacteria?

fMet-tRNAi^fMet

What is the initiator tRNA in eukaryotes?

Met-tRNAi^Met

Are the initiator tRNA the same as the tRNA that brings a methionine to internal sites of a polypeptide?

No. Although both carry methionine, they have different nucleotide sequences and 3D structures

What are the main components of the bacterial 30S initiation complex?

the small ribosome subunit, fMet-tRNAi^fMet , mRNA and three IFs

What are the three bacterial initiation factors?

IF1, IF2, and IF3

What is the function of IF1?

binds to the A site of the ribosome to prevent binding of other tRNAs during initiation

What is the function of IF2?

in complex with GTP, it recognizes the charged initiator tRNA, and assists its binding to the 30S subunit

What is the function of IF3?

prevents premature reassociation of the ribosomal subunit

Correct attachment of the mRNA to the 30S subunit in bacteria and archaea is accomplished by aligning the

Shine-Dalgarno (SD) sequence with a complimentary ribosomal RNA sequence (16S)

What are the main components of the eukaryotic 43S pre-initiation complex?

the small ribosome subunit, eIF2-GTP, Met-tRNAi^Met , mRNA, and multiple IFs

What is the main function of the eIF4F complex?

remove mRNA secondary structures that would otherwise inhibit the scanning process

What are the subunits of eIF4F?

eIF4A, eIF4E, eIF4G

elF4A

helicase

elF4E

cap binding

elF4G

scaffolding

What is the major functional difference between the 48S open complex and 48S closed complex?

the open complex scan along the mRNA for start codon, while the closed complex cannot scan

What are the main differences between translation initiation in bacteria and that in eukaryotes?

initiator tRNA, SD sequence, more IFs in eukaryotes

What are the main steps and players involved in translation elongation?

Major steps: binding of aminoacyl-tRNA, peptide bond formation, and translocation; Major players: ribosome, mRNA, charged tRNA, EF-Tu-GTP, EF-G-GTP

What are the irreversible steps in the translation elongation?

peptidyl transfer, and translocation

What signals the termination of elongation?

stop codon

What are the major factors involved in the translation termination?

release factors, 1, 2 and 3, ribosome releasing factor (RRF), EF-G-GTP, and IF3

RF1 and RF2 recognizes

stop codons

RF3

removes RF1 and RF2

Which domain of the RFs is involved in the recognition of the stop codons?

PVT for RF1 and SPF for RF2 of domain 2 of the anticodon loop. Amino acid residues in the surrounding areas may also be involved

Are IF3 and EF-G functioning only in initiation and elongation of translation, respectively?

No. IF3 is plays a role in both initiation and termination, while EF-G is involved in both elongation and termination