Question

A new operon is discovered with 5 genes.  How many promoters with a -10 and -35 region for sigma factor binding does it have?  How many ribosome binding sites (Shine Delgarno sequences)?  Explain your answer.

Answer 1

Answer-

1. Operon is set of structural genes that are regulated by regulatory genes. In prokaryotes mRNA is polycistronic that means single mRNA can synthesize more than one proteins but all these genes are regulated by single promoter-10 and -35.

2. So that this new operon with 5 genes has one promoter with -10 and -35 region for sigma factor binding. Once the RNA polymerase binds the promotor, it transcribes all genes of operon continuously .

3. In prokaryotes single mRNA can be translated by many ribosomes at a time and this is known as polyribosome . Here 5 ribosome binding sites are present at upstream of each gene of operon. Each gene in operon has ribosome binding site so that mRNA transcript can be translated by different ribosome at a time and single mRNA can synthesize many proteins at a time as these proteins are related to single function like in lac operon lacZYA genes synthesizes three proteins that are required for lactose metabolism.