1. Control of Gene Expression

2. Much Diversity due to Gene Expression
Each tissue in our body is very different despite having the same DNA
Even identical twins have many differences due to gene expression

3. Operons Simple gene expression mechanisms in prokaryotes
Not thought to be present in eukaryotes

4. Components of the Operon
Operator, sequence next to the promoter
Promoter (where RNA polymerase binds)
Genes that work together

5. Basic Function of Operons
Binding of regulatory molecules to the operator controls the transcription of the gene

6. Types of Operons Some genes are normally “off” and can be turned “on”
Presence of a molecule induces gene expression or enhances gene expression
Some genes are normally “on” and can be turned “off”
Presence of a molecule represses gene expression

7. Inducing Gene Expression
Bacteria only need lactase when lactose is present
Regulatory gene codes for repressor protein
Binds to operator, blocking promoter

8. Inducing Gene Expression (+ control)
Presence of lactose disrupts the regulatory molecule, allowing gene expression

9. Inducible Operon Regulatory mRNA Lactase RNA Transcription Blocked
Allolactose (inducer)
RNA Polymerase

10. Enhancing Gene Expression
Instead of a repressor molecule, an enhancer molecule binds to the operator
Helps facilitate binding of RNA polymerase and increases gene expression

11. Repressible Operon The repressor is normally inactive
A molecule (sometimes even the gene products) activates the repressor, shutting off gene expression

12. Repressing Gene Expression (- control)
Repressor is normally inactive, but can be activated
Active Repressor
Inactive Repressor
No More Transcription
RNA Polymerase

13. More Complex in Humans Pre-transcriptional control
Post-transcriptional control
Post-translational control

14. Regulatory Sequences
Stretches of DNA that interact with regulatory proteins like transcription factors (non-coding)
I.e. the promoter
Enhancers are sequences that increase transcription

15. Code for proteins or mRNAs which affect gene expression e.g. microRNAs
Regulatory Genes
Code for proteins or mRNAs which affect gene expression
e.g. microRNAs
Repressor proteins
Transcription factors/ enhancers

16. Access to the DNA
Is wrapped up in histone proteins forming nucleosomes

17. Wrapped DNA… Does not tend to get expressed
Condensing the DNA and causing more of it to be wrapped shuts off DNA expression
Loosening up DNA increases gene expression

18. Gene Activation

19. Gene Acetylation (activation long-term)

20. Genes can also be Deactivated

21. DNA Methylation

23. The Epigenome Epi = above, or in addition to
Lots of research now into how epigenome is passed on and changed
Your actions affect your epigenome
Your epigenome is passed on (sometimes)

24. Post-Transcriptional Modification
mRNA gets modified or broken down
Example microRNAs bind to mRNA and prevent translation from occurring

25. Post-Translational
Enzymes can modify or alter protein products

26. Millions of Proteins from 20k genes

27. The Main Point Genes can be turned on and off
These on/off switches can be short term or long term and might be passed down
Environment plays a huge role in the epigenome

28. Animation In pairs, animate out: Repressible operon Inducible operon
DNA methylation
Histone Acetylation