Question

a) Define a cistron.

b) Giving examples differentiate between monocistronic and polycistronic transcription units.

Answer 1

a) Cistron:

A cistron is defined as a functional unit of gene, it is the segment of DNA coding for a polypeptide. Cistron may code for one or more functional polypeptides.

b)

Difference between Monocistronic transcription unit and Polycistronic transcription unit

Criteria	Monocistronic transcription unit	Polycistronic transcription unit
Number of polypeptide produced	Monocistronic DNA segment directs the synthesis of only one polypeptide in one round of translation.	Polycistronic DNA segment directs the synthesis of more than one polypeptide in one round of translation.
Introns	Monocistronic DNA has introns	Polycistronic DNA has no introns.
Diagrammatic representation	Monocistronic mRNA (Eukaryotes)	Polycistronic mRNA (Prokaryotes)