Transcript Gene Regulation: Prokaryotes and Eukaryotes

Gene Regulation:
Prokaryotes and Eukaryotes
Chapter 11
Lac Operon
OPERON
Regulatory
gene
Promoter Operator
Lactose-utilization genes
DNA
mRNA
Protein
RNA polymerase
cannot attach to
promoter
Active
repressor
Operon turned off (lactose absent)
DNA
RNA polymerase
bound to promoter
mRNA
Protein
Lactose
Inactive
repressor
Operon turned on (lactose inactivates repressor)
Enzymes for lactose utilization
Trp Operon
trp operon
Promoter
DNA
Promoter
Genes of operon
trpD
trpC
trpE
trpR
trpB
trpA
Operator
Regulatory
gene
mRNA
5
3
RNA
polymerase
Start codon
Stop codon
mRNA 5
E
Protein
Inactive
repressor
D
C
B
A
Polypeptides that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on. RNA polymerase attaches to the DNA at the
promoter and transcribes the operon’s genes.
Trp Operon
DNA
No RNA made
mRNA
Protein
Active
repressor
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off. As tryptophan
accumulates, it inhibits its own production by activating the repressor protein.
Levels of Chromatin Packing
X chromosome Inactivation and
Tortoiseshell Cat
Tortiseshell Cat
X chromosome Inactivation in a
Calico Cat
Cellular Differentiation
Muscle cell
Pancreas cells
Blood cells
Enhancers
Promoter
Gene
DNA
Activator
proteins
Transcription
factors
Other
proteins
RNA polymerase
Bending
of DNA
Transcription
Eukaryotic
Transcription:
Enhancers,
Activators
Production of two different mRNAs
from the same gene
Exons
DNA
RNA
transcript
or
RNA splicing
mRNA
Alternative Gene Splicing
NUCLEUS
Chromosome
Overview:
Opportunities for gene
regulation in
eukaryotic cells
DNA unpacking
Other changes to DNA
Gene
Gene
Transcription
Exon
RNA transcript
Intron
Addition of cap and tail
Tail
Splicing
mRNA in nucleus
Cap
Flow through
nuclear envelope
mRNA in cytoplasm
CYTOPLASM
Breakdown of mRNA
Translation
Brokendown
mRNA
Polypeptide
Cleavage / modification /
activation
Active protein
Breakdown
of protein
Brokendown
protein