The gal yeast system and chromatin structure Flashcards
What can be used as a energy source is the absence of glucose by yeast?
galactose
What enzymes are involved in the import and metabolism of galactose?
Gal2, Gal1, Gal7, and Gal10
What are regulatory proteins in the yeast GAL system?
Gal4, Gal3, Gal80
If there’s no galactose are enzyme encoding genes expressed?
NO, Gal7, Gal10, Gal1, and Gal2 are not expressed
If there is galactose are enzyme encoding genes expressed?
YES! GAL7, GAL10, GAL1, AND GAL2 are expressed
Are all enzyme encoding genes in the yeast GAL system on the same dna strand?
NO, on different DNA strands
What are the three parts of the GAL4 enzyme?
An activation domain, a dimerization domain, and a DNA-binding domain
Is GAL4 a transcription factor or coregulator?
transcription factor as it has a DNA binding site
What does GAL4 bind to to initiate transcription?
Binds to upstream activation sequence (UAS)
What is UAS?
An enhancer sequence
How many UAS are upstream of all GAL genes?
2
Is GAL4 always expressed?
Yes, it’s always there
What is a repressor of GAL4?
Gal80
What other two enzymes (outside of GAL4) are always expressed?
Gal3 and Gal80
How does Gal80 repress GAL4? What is the outcome of this repression?
Gal3 undergoes a confirmational chnage in the presence of galactose which allows it to bind to gal80 which stops the repressor from binding to gal4. This allows the GAL4 to be active and initiate transcription
Define a chromatin?
A complex of
DNA and proteins that
make up eukaryotic
chromosomes
Why is it harder for transcription factors to get in eukaryotic chromosomes?
Because chromatin is 10,000X more compact than linear DNA
Define a nucleosome?
Is histones with DNA wrapped around it
Histone octomers are composed of what?
Composed of 8 proteins, two of each H2A, H2B, H3, H4
Histones are _____ charged
postively charged
How does the charge of histones interact with DNA to form compaction?
DNA wraps around histones cause it’s overall negatively charged
Histones contain a ______ core and flexible ________
folded up, tails
What do the tails in histomes interact with?
Tails interact with different proteins and nearby nucleosomes
What is the most compacted region of chromosomes?
Constitutive heterochromatin
Where can we find constitutive heterochromatin?
in regions not transcribed
What is facultative chromatin?
Type of heterochromatin, can open or close in certain conditions
What is the open form of facultative heterochromatin?
euchromatin
What are the two types of hetero chromatin?
Constitutive heterochromatin and facultative heterochromatin
What two types of modification can result in chromatin modification?
Histone modification and DNA modification
Where does most modification happen in histomes?
on tails
What is chromatin remodelling?
Physically repositioning/ removing/
replacing histone octomers along
the DNA
What is a type of histone modification?
acetylation
Define histone acetylation?
addition of an acetyl
group to a lysine amino acid
What are the two effects of acetylation?
Reduces chromatin compaction as it causes neutral charged amino acids which then loosens the interaction between histomes and DNA
Creates a binding site for a protein domain called bromodomain found in transcriptional factors
What is the overall impact of histone acetylation?
increasing transcriptional activation
What adds acetyl group to histone tail?
histone acetyltransferase
What removes acetyl group from histone tail?
histone deacetylase
What is the histone code hypothesis?
Proposes that different combinations of histone modifications specify different
transcription outcomes
