1. 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?

2. Typical Gene Regulation
See page 309 in your textbook Figure 12-22
Regulatory sites
promoter
start
stop
gene
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

3. Prokaryotic Gene Expression usually uses OPERONS
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!

4. 3. Three genes for making proteins involved in breaking down lactose
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

5. 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)

6. Without Lactose:

7. With Lactose:

8. Lac operon animation

9. 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!

10. Eukaryotic Gene Regulation
See page 311 in your textbook Figure 12-24
exon
enhancer
Promoter sequences
TATA Box
intron
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

11. Proteins that bind to enhancer sequences of a gene can work to:
Open up tightly packed chromatin.
Attract RNA polymerase.
Block access to genes.

12. RNA Editing unit of transcription in a DNA strand exon intron exon3’ 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

13. Prokaryotic vs. Eukaryotic Gene Expression

14. Hox genes

15. 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.