Question

Which of the following is not an essential function of ribosomes in all domains of life?

	A.	Catalyze peptide bond formation between amino acids during polypeptide formation.
	B.	Bind messenger RNA and identify the start codon where translation begins.
	C.	Facilitate the complementary base pairing of mRNA codons and tRNA anticodons that determines amino acid order in the polypeptide.
	D.	Align the Shine Delgarno sequence in the mRNA with a complementary sequence in the 16S rRNA of the small ribosomal subunit.

Answer 1

Ribosome is a cellular organelle, found in all living organisms. It is found either in cytoplasm or attached with endoplasmic reticulum. Ribosomes made up of two subunits, one large subunit and one small subunit. In bacteria 70s ribosomes are found , small subunit 30s and large subunit 50s. In eukaryotes it is 80s, small subunit 40s, large subunit 60s.

The main function of the ribosome is assembly of amino acids during protein synthesis. The ribosome has 3 binding sites, A,P and E. At the A site, an aminoacyle-tRNA complementary with mRNA binds. At P site, t-RNA binds with the synthesized peptide chain. From E site the t-RNA exists. During translation of mRNA tRNA brings amino acids attached with it . There are several tRNAs present in the cell. These tRNA contains complementary anti codon of mRNA at its anti codon loop.

Translation begins with the recognition of start codon on mRNA by the ribosome. Ribosomes recognizes the start codon by using a constant region on mRNA located upstream of the start codon. In prokaryotes this region known as Shine-dalgarno sequence and In eukaryotes this region known as Kozak sequence.

So , the non essential function of ribosome is (option D) Align shine-Dalgarno sequence in the mRNA with a complementary sequences in the 16s rRNA of the small ribosomal subunit.