Polycistronic gene

Ncert plus two biology surendran aduthila

1. Gene Structure:
Polycistronic vs monocistronic
•Cistron: an old name for a gene
•Polycistronic: 1 promoter directs
synthesis of 1 mRNA that can be
translated to more than one
polypeptide
–Prokaryotic genes
•Monocistronic: 1 promoter directs
synthesis of 1 mRNA that usually
translates to only 1 protein
–Eukaryotic genes

2. Monocistronic vs Polycistronic
Transcription
•Prokaryotes – Both
•Eukaryotes
1.Nucleus – Monocistronic (polycistronic rare)
2.Mitochondria
–Mammals – polycistronic (2 promoters); pre-
RNAs processed into smaller species
–Other – Both
–Chloroplast - Both

3. Why does prokaryotes have
polycistronic while eukaryotes have
monocistronic?
•Eukaryotes don’t need everything so by
using monocistronic, they can regulate
what is being created without creating too
much of unnecessary resources.
•Prokaryote uses polycistronic because
they genome is small and want to make
everything in one pathway together.

4. The lac Operon
P O lacZ lacY lacA
P O lacZ lacY lacA
mRNA 5’ 3’
RIBSOSOME BINDING SITE
Q: How many proteins are made?