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Lecture 15

Biology 1202B Lecture Notes - Lecture 15: Histone H3, Dosage Compensation, Heterochromatin

Course Code
BIOL 1202B
Patrick Mc Donald

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Kaden VanHelden
Biology 1202B: Lecture 15 – Regulation of Gene Expression II
Lac Operon
Main product of lac Z is Beta-galactosidase
What is the effect of various mutations on the production of lac Z protein
Effect of removing lac Y gene on lac Z production
oLac Y allows lactose into the cell
oRemoving lac Y reduces the expression of lac Z protein
Effect of removing lac I promoter
oLac I synthesizes repressors
oRemoval of lac I increases the expression of lac Z protein
“An epigenetic trait is a stably heritable phenotype resulting from changes in a
chromosome without alterations in the DNA sequence”
Epigenetics = regulation of gene expression
oAlter the level of chromatin compaction
Euchromatin (loosely bound – active)
Heterochromatin (tightly bound – silent)
Active = available for transcription
Silent = too tightly bound to be available for transcription
Chromatin remodelling
Processes are heritable, but reversible
Means of differential gene expression between cell types
oSkin cell is a skin cell because of epigenetic modifications
oIf a cell doesn’t need to transcribe something it doesn’t – this saves energy
Epigenetic mechanisms
Histones are proteins (have an N end and a C end)
Histone modifications and methylation determines if chromatin is active or silent
Histone modifications define chromatin
Histones have dozens of sites for modifications to occur
Histones are modified by methylation, acetylation, phosphorylation, and others
Combinations of specific histone modifications define the function of local regions of
oCalled the “histone code” – hasn’t been completely deciphered yet
Histone acetylation
Histones have a positive charge
oAllows binding to negatively charged DNA
Acetylation masks positive charge
oWeakens DNA-histone binding by reducing positive charge
oReduces chromatin compaction – doesn’t mean gene is on, just available
oAllows for transcription
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