BIOL SCI 215 Lecture Notes - Lecture 11: Lac Operon, Tata Box, Lac Repressor
28 Jun 2018
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5/11 Eukaryotic Regulation
Lac operon: system in bacteria
oNeed a carbon source such as lactose to start the reaction
Regular arrow: Positive interaction
---| arrow: Negative Interaction
Lactose (Metabolite/Inducer which means it has a positive influence)--| LacI(which
binds to DNA) → LacO which is a DNA sequence (landing site) → regulate LacZ
expression
oNo LacI means that LacZ will be constitutively expressed
oLacI conformational shape changed by Lactose as recognition that lactose is
present
Glucose and cAMP levels inversely proportional
CAP, a protein, binds to DNA with high cAMP, facilitates binding for RNA polymerase
When glucose is high and lactose is present, there still won't be any CAP binding
because there is no activator present
oCell prefers to metabolize glucose over lactose
mRNA synthesis in eukaryotes is more complex than in prokaryotes
mRNA translated in the cytoplasm
In order to activate transcription: Promoter (TATA box) upstream of the coding
sequence, Enhancers located downstream of genes where they bind to protein
transcription factors called activators where activators recognizes bases on
enhances and bring it to mediator, and then the mRNA polymeraese will start the
transcription.
Positive and negative signals modulate the probability of transcription initiation
Organization/Characterization of DNA
In eukaryotes but not bacteria, DNA is wrapped around histones
First level: DNA wrapped around nucleosomes, at a distance apart from each other
Nucleosomes made up of Histones and DNA
Several configurations
Heterochromatin: regions of the genome that are silent because the chromosome is
so compact by the nucleosomes
When histones are methylated, they are inactivated for expression that would create
heterochromatin
Histones can carry through many generations
Each histone has a tail and is together as a bunch,
Galactose binds to enhancers upstream of UAS sequences
Gal4 activated only when Galactose is near the cell. In absence of Galactose, it is inactive
but Gal80 binds to UAS
gAL3 is a sensor but does not bind
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Document Summary
Lac operon: system in bacteria: need a carbon source such as lactose to start the reaction. Cap, a protein, binds to dna with high camp, facilitates binding for rna polymerase. Positive and negative signals modulate the probability of transcription initiation. In eukaryotes but not bacteria, dna is wrapped around histones. First level: dna wrapped around nucleosomes, at a distance apart from each other. Nucleosomes made up of histones and dna. Heterochromatin: regions of the genome that are silent because the chromosome is so compact by the nucleosomes. When histones are methylated, they are inactivated for expression that would create heterochromatin. Each histone has a tail and is together as a bunch, Galactose binds to enhancers upstream of uas sequences. Gal4 activated only when galactose is near the cell.
