1. Why genes are regulated
Organisms respond to environment - e.g. nutrients available
Multi-cellular organisms must have different cell types (differentiation)
Genes must be switched on/off at correct times and in correct cells
Gene regulation is complex and precisely controlled process

2. DNA does not change
All cells in an organism have the same set of genes (usually)
DNA sequence does not change but genes can be switched on/off
Gene regulation must be a reversible process
Some gene activities are required in all cell types (housekeeping genes) e.g. synthesis of RNA
Others are tissue specific e.g. to make muscle proteins (myosin, actin) in muscle cells

3. Any cell has all genes to make frog
Adult frog
Unfertilised egg
Skin cell removed
and cultured
Destroy nucleus
by UV light
Nucleus removed
and micro-injected
into egg
Normal embryo
Normal tadpole

4. Regulation at what stage?
DNA
RNA
Protein
Transport,
Processing
transcription
translation
Active
protein
Several places at which regulation could occur
Mostly regulated at transcription stage
Most economical - don’t make things that aren’t needed
Achieved by specific proteins that bind to DNA

5. DNA binding proteins
Specific proteins bind to specific points in the DNA
The two fit together like a lock and key
Almost all genes are regulated this way
DNA
Protein

6. Gene regulation in bacteria
Simple systems to turn genes on and off
Response to nutrients e.g. if tryptophan (an amino acid) is in the medium, don’t need to make your own
Similar systems exist for other amino acids
Turning a gene off is repression

7. Tryptophan (trp) gene regulation
Trp operon
promoter
E D C B A
trp synthesis enzymes
DNA
RNA
No trp
Trp present
Repressor
protein
RNA polymerase
No transcription

8. Gene activation
Bacteria turn on genes to use sugars for energy when available
Turning genes on is activation
Also uses specific DNA-binding proteins
protein
DNA
RNA
RNA polymerase
Activator
Environmental
stimulus
Promoter

9. Gene regulation in eukaryotes
Genes have to be switched on by regulatory proteins, otherwise would do nothing
General proteins in all cell types, special ones in specific cell types
Regulatory proteins bind to sites in DNA called enhancers
Enhancers can be 1000s of bp away from gene

10. Gene regulation in eukaryotes
Specific activator
protein
Promoter
Enhancer
RNA polymerase
& general transcription factors

11. Drosophila eye development
Cells for eye
Cells for leg
Larva
Adult
Normal
Ey gene artificially
expressed in cells for leg
“Eye” on leg