Question

How does translation initiate, what role does the 5' cap play, and what happens when cap-dependent translation is no longer possible? What role do the 5' and 3' UTRs play in controlling gene expression? Can the polyA tail play a role in initiating translation? Must the small ribosome binding site be 5' to the start codon?

Answer 1

Translation is the process of protein synthesis from the mRNA. Translation initiate when small ribosomal unit binds with the mRNA sequence. After that, tRNA carrying the amino acid methionine binds to start Codon which is "AUG". Hence in this way, according to the Codon present in mRNA, amino acid are being added at the ribosome.

Role of 5' cap in mRNA is to protect mRNA from degrading so that translation get started as soon as transcriptions is completed. The cap is modified guanine residue.

When cap dependent translation does not takes place, translation stops.

5' UTR(untranslated region) is the region in the mRNA which is recognized by ribosomes and they bind to it and help in initiation of translation whereas 3'UTR play give signal to stop the translation. Hence, in this way they play an important role in gene expression in the form of protein.

No, the poly A tail will not be able to initiate translation because it will not have the binding site for ribosome attachment that are necessary for initiation of translation.

Yes, small ribosome should bind to the 5' of the codon because only then the imitation of translation takes place.