Question

What is the Shine-Dalgarno sequence? What binds to the sequence during translation? Describe some of the ways in which the sequence can vary, addressing the consequences that any such variation has on translation efficiency. Be very thorough with your answer.

Outline the steps of the ribosome cycle. At what stage do the ribosomal subunits bind to each other? To mRNA? What causes them to dissociate when protein synthesis is complete? Be specific.

Answer 1

Shine-Dulgarno sequence is a conserved sequence in the mRNA of prokaryotes that enable them to bind to the 16s rRNA. It is a purine rich region towards the 5’ untranslated region of the mRNA, with the sequence 5’ – GGAGGU – 3’. This is complementary to the sequence 5’ ACCUCC – 3’ of the rRNA. Shine Dulgarno sequence is located about 10 bp upstream of the start codon.

The sequence may vary slightly, it can be either AGGAGG or AGGAGGU. The sequence GAGG is consenses sequence that generally is preserved.

Ribosome cycle is the formation of functional ribosomes. Ribosomes exist as free forms in the cytoplasm. During protein synthesis, the free subunits of the ribosomes associate together to form a functional ribosome. Ribosome cycle was demonstrates by R.O.R. kaempfer, Meselson, and Raskas.

The smaller subunit of prokaryotic has 16 S RNA, and the larger subunit has 5 S and 23 S RNA. During initiation of protein synthesis, 16 S RNA interacts with mRNA, for form rRNA – mRNA complex.