1. Regulation of Gene Expression
Chapter 18

2. YOU MUST KNOW
Genes can be activated by inducer molecules, or they can be inhibited by the presence of a repressor as they interact with regulatory proteins or sequences
A regulatory gene is a sequence of DNA that codes for a regulatory protein such as a repressor protein
How the components of an operon function to regulate gene expression in both repressible and inducible operons
How positive and negative control function in gene expression
The impact of DNA methylation and histone acetylation on gene expression
How timing and coordination of specific events are regulated in normal development, including pattern formation and induction
The role of microRNAs in control of cellular function
The role of gene regulation in embryonic development and cancer

3. Operons Clusters of genes in bacterial chromosomes 3 parts
Allows expression of several related genes to be controlled as a unit
3 parts
Operator – controls access of RNA polymerase to genes
Found within the promoter or between the promoter and the coding genes
Promoter – where RNA Polymerase attaches
Genes

4. Regulatory genes
Located a distance away from the operon
Code for proteins that may bind to the operator
When that protein occupies the operator, RNA Polymerase cannot access genes of the operon (genes turned off)

5. Repressible Operons
Usually on and generally anabolic (build essential biomolecules)
Repressor protein produced from regulatory gene is inactive
Biomolecules coded for by the operon acts as a corepressor – binds to the repressor and activates it
So if biomolecule is already present in the cell, the operon is turned off

6. Inducible Operons
Normally off and generally catabolic (break down molecules)
Repressor protein produced by regulatory gene is active
In order to deactivate the repressor protein, an inducer must be present – when inducer is bound to repressor, it can’t block transcription of the operon

7. Eukaryotic Gene Expression
Differential Gene Expression – expression of different genes in different cells
DNA methylation – addition of methyl groups to DNA, reducing gene expression
Histone acetylation – acetyl groups added to histones, loosening the coiling of nucleosomes, increasing expression

8. Transcription initiation – regulation of the binding of transcription factors
Transcription initiation complex – enhances gene expression
Enhancer regions – DNA sequences far from the gene (enhancer regions) produce proteins called activators

9. Other mechanisms in eukaryotes
Epigenetic inheritance – inheritance of traits by mechanisms not directly involved with nucleotide sequence
mRNA and protein processing
Coordination of gene expression of related genes – genes for one metabolic pathway may be scattered on different chromosomes, but they share the same control elements

10. Noncoding RNAs RNA interference
Micro RNAs (miRNA) and small interfering RNAs (siRNA) bind to mRNA and either degrade it or block its translation

11. Cell Differentiation Development of the zygote
Cell division – repeated mitosis to increase the number of cells
Cell differentiation – cells become specialized in structure and function
Morphogenesis – organism gains it shape

12. Cytoplasmic determinants – maternal substances in the egg that influence early development
Uneven distribution around cells of the embryo
Cell-cell signals – molecules produced by one cell influence neighboring cells
Induction – signal from a neighboring cell causes cell to differentiate
Determination – series of events that cause differentiation

13. Pattern formation
Sets up body plan for the developing organism (head, tail, left, right, etc.)
Morphogens – substances that determine these axes (unevenly distributed)
Homeotic genes – master control genes for pattern formation

14. Cancer and cell cycle genes
Oncogenes – cancer causing genes
Proto-oncogenes – code for proteins responsible for normal cell growth – become oncogenes when mutated

15. Tumor-suppressor genes – products normally inhibit cell division
p53 gene – product suppresses cancer in four ways
Can activate the p21 gene – product halts the cell cycle by binding to cyclin-dependent kinases. This allows DNA to be repaired before cell division
Activates miRNAs that inhibit the cell cycle
Turns on genes involved in DNA repair
When DNA damage is too large to repair, activates genes which cause apoptosis
Note: embryonic development is an example of gene regulation is done correctly, cancer is when gene regulation goes wrong