1. Gene Expression and Regulation

2. Warm Up What enzyme binds to DNA to help produce an mRNA strand?
What are the two steps to producing a protein?
What is a gene?

3. Gene Regulation Process of turning genes on and off
Ensures that the appropriate genes are expressed at proper times

4. How does an organism know whether to turn a gene “on” or “off”?
Gene Regulation
Only a fraction of the genes in a cell are expressed at any given time
Only 3-5% at any one time!
If we look closely at the order of DNA bases we notice that certain DNA sequences serve different purposes but…
How does an organism know whether to turn a gene “on” or “off”?
For example:
Promoters: binding sites for RNA Polymerase
Start/Stop signals for transcription
There are specific sequences for promoters, on a eukaryotic cell it is known as a TATA box
We keep it from being transcribed and translated!!
To explore this question we are going to look at the lac operon

5. Gene Regulation: Terms to know!
Promoter: Region of DNA that indicates to RNA Polymerase where to bind to make RNA
Operator: Region of chromosome to which repressors bind
Repressor: binding protein that inhibits the expression of one or more genes by binding to the operator
Inducer: molecule that starts gene expression

6. Operons
An operon is a group of genes that are transcribed at the same time.
They usually control an important biochemical process.
They are only found in prokaryotes.
Jacob, Monod & Lwoff

7. Background Information
Bacteria can synthesize different enzymes (proteins) depending on what food substrate they are growing on
E. Coli can synthesize over 3000 different enzymes!
Enzymes that are involved in basic cell functions are synthesized at a constant rate
Inducible enzymes are synthesized as and when they are needed

8. Background Information
E. Coli typically utilizes Glucose as its energy source but can also use Lactose (a dissacharide)
In order to use Lactose as food E. coli must do 2 things:
Take lactose across the cell membrane
Break the bond between glucose and galactose
To do these 2 things, E. Coli needs to synthesize two enzymes

9. Background Information
ß-galactosidase- Hydrolyses lactose into glucose and galactose
lactose permease – transport protein that becomes embedded in the E. Coli membrane – helps transport more lactose into the cell
Because lactose triggers the production of enzymes it is the INDUCER in this operon.
When placed in a lactose substrate, E. Coli increases the synthesis of these two proteins by 1000x

10. The lac operon
Lac system genes (in the bacterial DNA) form the operon – consists of structural genes and control genes.
Z - ß-galactosidase
Y - lactose permease
O – Operator region – switches Z & Y on and off
P – Promoter; binding site for RNA polymerase for transcription of Z & Y
NO INDUCER = making of the REPRESSIOR PROTEIN

11. If lactose is ABSENT…
Regulator gene is expressed and produces repressor protein
Repressor protein binds to the operator region (P & O)
Partially covers the promoter region (P)
RNA polymerase can’t bind – Z & Y genes can’t be translated
Z & Y are switched off

12. If lactose is PRESENT…
Inducer molecule (lactose) binds to the repressor protein
Repressor protein dissociates from the operator region
Promoter is now unblocked
RNA polymerase can now bind promoter region
Z &Y can now be transcribed – mRNA produced
ß-galactosidase /lactose permease can now be synthesized

13. The lac operon
As a result of the 2 enzymes being made, E. Coli can now.....
Take up lactose from its environment because lactose permease acts a transport protein.
Using ß-galactosidase, lactose (disaccharide) can hydrolyzed into glucose & galactose
E.coli can use these sugars for respiration
E.coli is gaining energy from the lactose

14. Follow-Up Activities Log onto EdPuzzle and watch the Lac Operon video
Follow the link for the gene regulation animation
Read the Introduction & take brief notes
Watch the animation
Pay close attention to the box that says Lactose and Results!
Read and take brief notes on the Conclusion
Take the quiz at the end of the simulation
Write the questions in your notebook!

15. Follow-Up
Using the pieces provided and your phone, create a picture collage of what happens when regulator is present vs when it is not present.
Label your pictures LACTOSE PRESENT or LACTOSE NOT PRESENT
Draw your final products in your Notebook
Use your sources to help you!

16. Q.1 match the components with the functions.
Exit Ticket:
Q.1 match the components with the functions.
Q.2 What are the functions of:
Repressor protein
RNA polymerase
Regulatory gene
Component
Function
A. Structural Gene
1. Produces repressor protein
B. Regulatory gene
2. Binds to repressor
C. Promoter
3. Codes for lac enzymes
D. Operator
4. Binds to RNA polymerase