Transcript Eukaryotic Gene Regulation

Gene Regulation
• An expressed gene is one that is
transcribed into RNA
• Not all genes are expressed by every cell
• How does an organism know when to “turn
on” or “turn off” a gene?
Typical Gene Regulation
•
See page 309 in your textbook
Figure 12-22
stop
start
gene
promoter
Regulatory sites
Promoters- DNA sequence where RNA polymerase will bind
Operator (regulatory sites)- stretches of DNA where proteins can bind to
regulate transcription
Start and stop signals- for transcription of gene
Prokaryotic Gene Expression
usually uses OPERONS.
OPERONS- are a group of genes
that operate together
the Lac operon is a great example!
It’s a set of genes needed for E.coli
to make proteins so the bacteria
can use the sugar lactose as food!
The Lac operon has
1. a promoter (the nucleotide sequence where
RNA Polymerase binds- green)
2. an operator (segment of DNA used to turn
gene expression on or off, repressor protein
binds here- dotted/shaded region)
3. Three genes for making proteins involved in
breaking down lactose
See
page 310
Fig.12-23
How the Lac Operon works or operates….
Lac genes turned OFF by the repressor protein and
turned ON by the presence of Lactose
WITHOUT Lactose- DNA binding protein is bound to the
OPERATOR (where protein binds) so RNA polymerase
CAN’T WORK (can’t make the mRNA)
WITH Lactose- lactose binds to repressor DNA binding
protein, this causes the protein to CHANGE SHAPE and
FALL OFF the DNA Operator so RNA polymerase CAN
WORK (transcribes the gene)
Without Lactose:
With Lactose:
Lac operon animation
• http://www.sumanasinc.com/webcontent/a
nimations/content/lacoperon.html
Eukaryotic Gene Regulation:
• Most eukaryotic genes are controlled
individually NOT with operons
• Only a few of the available genes will be
expressed in the cells of different tissues
(cell specialization/differentiation)
• Complex!
Eukaryotic Gene Regulation
See page 311 in your textbook
Figure 12-24
TATA Box
exon
enhancer
intron
exon
intron
exon
Promoter
sequences
Enhancer sequence- lots of proteins can bind here on different sequences
(that’s why eukaryotic gene regulation is more
complex!!)
Promoters- usually just before the TATA Box (where RNA polymerase binds)
TATA Box- helps position RNA polymerase in front of gene
Exons- expressed
Introns- cut out before translation
Proteins that bind to enhancer
sequences of a gene can work to:
a. Open up tightly packed chromatin.
b. Attract RNA polymerase.
c. Block access to genes.
RNA Editing
unit of transcription in a DNA strand
exon
intron
exon
intron
exon
3’
5’
transcription into pre-mRNA
poly-A
tail
cap
5’
3’
(snipped out)
(snipped out)
5’
3’
mature mRNA transcript
Fig. 14.9, p. 229
Prokaryotic vs. Eukaryotic
Gene Expression
• http://highered.mcgrawhill.com/sites/0072437316/student_view0/
chapter15/animations.html#
Hox
genes
Development and Differentiation
• Hox genes are master control genes that
control the differentiation of cells and
tissues in the embryo.
• A mutation in hox gene in fruit flies had a
leg growing where antenna should be.