1. Gene Expression and Regulation
Chapter 12-5

2. All of your cells contain the same DNA.
Your nerve cells do not look like or act like skin cells, so how do they know what to do and what to produce?
Genes are to be turned on or turned off based on whether they will be used or not
When a gene is actually transcribed and translated, it is said to be expressed.

3. I. Basic Structure of a gene
When looking at a gene sequence, there are several important regions that enzymes and other proteins recognize.
Regulatory sites
Promoter
Start transcription
DNA strand
Stop transcription

4. 1. Promoter- region of gene where RNA Polymerase binds
2. Start- transcription begins (TAC)
Stop- Transcription ends (stop codon)
Regulatory sites- near the promoter where regulatory proteins can bind (turn genes on and off)

5. II. Prokaryotic Gene Regulation
Prokaryotes have a single chromosome and are unicellular
Turn genes on and off when needed
Operon- group of genes that operate together for a function, can be
Inducible
Repressible

7. A repressor molecule can block, or repress, transcription by binding to a region called the operator.
Inducible- in presence of a substance, the substance causes the repressor to let go
Repressible- in presence of a substance, the substance causes the repressor to grab onto the operator

8. Example: lac operon
The lac operon is a series of genes in E. coli that operates together to metabolize (use as food) lactose, the sugar found in milk
Lactose is a disaccharide made of glucose and galactose
In the presence of lactose, certain enzymes must be produced to break them down

9. Example: lac operon

10. P (promoter)- region that RNAP binds
O (operator)- region that a repressor can bind, blocking RNAP from transcribing
Gene Z- codes for β-galactosidase
which breaks down lactose into glucose and galactose
Gene Y- codes for Permease
Which causes the cell membrane to be more permeable to lactose (let it in)
Gene A- codes for a protein whose function is unknown

11. Steps for lac operon
In absence of lactose, a repressor binds to the operator, blocking RNAP
1. In the presence of lactose, lactose binds to the repressor causing it to let go of the operator
2. RNAP transcribes gene Z (makes β-galactosidase) and gene Y (makes permease)
3. Ribosomes translates β-galactosidase and permease

12. 4. β-galactosidase breaks down lactose into glucose and galactose
5. Permease allows lactose to flood into the bacterial cell
6. Once lactose is all broken down, lactose lets go of the repressor so it can rebind to the operator
7. This stops transcription and translation of β-galactosidase and permease

14. III. Eukaryotic Gene Regulation
No operons, genes are regulated individually
Similar process, but is much more complex than prokaryotic gene regulation
Prokaryotes have no cell specialization

15. There is a promoter region, several enhancer sequences and a “TATA box”.
TATA- helps position RNA Polymerase
enhancers can act like operators and block transcription, and others can signal to unpack chromatin

16. Exons actually get “EXPRESSED”
Introns are cut out of the mRNA copy and not transcribed and translated by ribosomes.

17. Differentiation is controlled by hox genes.
After fertilization and mitosis occurs, cells specialize into their life-long functions through a process called differentiation
Differentiation is controlled by hox genes.
Some genes get turned off permanently (your liver cells do not express genes that make proteins in the skin)
Like master controls of what cells become what part of the body
Manipulation of these genes can alter what parts grows where (a leg out of your head?!)