During Initiation of Translation

Question

During initiation of translation:
A)the initiator tRNAmet binds to the A site of a ribosome.
B)specific rRNA base pairs with a sequence in mRNA to position a ribosome at the start codon.
C)IF-3 must be recruited to the 30S ribosome in order for the 70S initiation complex to assemble.
D)there is no energy expenditure as the tRNA binding to mRNA is via complementary base pairing.
E)both 70S and 30S ribosome subunits must simultaneously recognize an mRNA to bind.

Accepted Answer

During initiation of translation, a specific rRNA base pairs with a sequence in mRNA to position a ribosome at the start codon. This is known as the Shine-Dalgarno sequence in prokaryotes or the Kozak sequence in eukaryotes. The initiator tRNA binds to the P site, not the A site, and the recruitment of IF-3 is necessary for 30S ribosome assembly, but not for the 70S initiation complex. There is some energy expenditure involved in the initial recognition and binding of the tRNA to mRNA. Both 70S and 30S ribosome subunits are involved in the initiation complex, but they do not need to simultaneously recognize the mRNA.