In which among the following organism monocistronic structural genes are present ?

Eukaryotes .

The correct answer is Option (2) -Eukaryotes.

Monocistronic structural genes are those that contain a single coding sequence responsible for producing a single protein product. These genes are commonly found in eukaryotes, while bacterial genomes, such as that of E. coli, often contain polycistronic structural genes.

Explanation:

• Bacteria (such as E. coli): Bacterial genomes often contain polycistronic structural genes, which means that a single mRNA transcript can encode multiple proteins, typically arranged in operons. Each operon contains multiple adjacent genes under the control of a single promoter and terminator sequences. Therefore, in bacteria like E. coli, the structural genes are often polycistronic.
• Eukaryotes: In contrast, eukaryotic genomes typically consist of monocistronic structural genes. In eukaryotic cells, each structural gene is transcribed to produce a single mRNA molecule that encodes a single protein. This one-gene-one-protein relationship is a characteristic feature of eukaryotic gene expression.

Therefore, monocistronic structural genes are a characteristic feature of eukaryotic organisms, while bacterial genomes, such as E. coli, commonly exhibit polycistronic structural genes.