Download 12.5 Gene Regulation

12.5 Gene Regulation
1. Gene Regulation
• In any organism, only a few genes are
expressed at each time
• Operon: group of genes that operate
together
• Scientists study E. coli gene expression of
the lac operon
2. E. Coli lac Operon
• Allows bacteria to use lactose (sugar) as
food
• Genes are turned off by repressors
• Genes are turned on by presence of
lactose in the cell
3. Removal of the Repressor
• Promoter: RNA polymerase binds to begin
transcription
• Repressor protein will bind to operator to
prevent transcription if it is not needed
– Once lactose comes into the cell, the
repressor will change shape and come off of
the operator
– Once the repressor is released, transcription
can happen
4. Eukaryotic Gene Regulation
• Generally, eukaryotes do not have
operons
• Eukaryotic regulation is much more
complicated than prokaryotic
• TATA box
– Shows where transcription should begin on
the gene
• Before the TATA box, the promoters are
found
5. Enhancer Sequences
• Where are they found?
– located before the point where transcription
begins
• What are three things they can do?
– Some will open tightly packed chromatin
– Some will attract RNA polymerase
– Some will block access to genes
6. Cell specialization requires gene
specialization
• All cells have all genes for that organism
• Some genes in certain cells will never be
used
• Example:
– Liver cells will never express the exact same
genes needed in nerve cells in the brain
7. Development and Differentiation
• Cell differentiation: when the embryo is
developing, the cells are not just going to
divide, they will turn into specialized cells
– Each of these specialized cells will have
specialized structure and function
Hox Genes
• Show where differentiation should occur
(cells and tissues)
• Master control gene
• Mutations in these genes can cause major
developmental problems
– Example: Drosophila melanogaster: replace
the fly’s antennae with it’s legs – so legs were
growing on the fly’s head
Hox Genes
•
Hox genes are extremely similar in living
things
–
Can be removed from one animal and put
into another and will still work
•
Example: mouse eye was put into a fly and the
fly grew an eye on it’s leg