Exam 3: Control of Gene Expression in Eukaryotes Flashcards
(32 cards)
Differences between gene control in bacteria vs. eukaryotes
B: Primary just transcription regulation, no role of chromatin structure, simple initiation of transcription, enhancers are less common, simultaneous transcription and translation, no regulation by small RNAs
E: Many levels of regulation, chromatin structure plays an important role, complex initiation of transcription, enhancers are more common, separate transcription and translation, and regulation by small RNAs
Pre-transcriptional regulation in E
levels of transcription are dependent on whether or not the DNA is available for transcription - epigenetics
Enhancers
Regulatory sequences found upstream of genes - the activator must bind to the enhancer, and they interact with transcriptional machinery to increase levels of transcription
Regulation of Galactose Metabolism in Yeast
Can transcribe anything you want to make transgenic expression of genes
Non-inducing conditions in yeast
Galactose is not present. The activation domain, GAL4, is blocked by a repressor, GAL80, that is bound to it. Transcription does not take place.
Galactose-inducing conditions in yeast
Galactose is present. GAL3 is allowed to enter the nucleus from the cytoplasm and is able to cause the unbinding of the repressor, GAL80, from the activation domain, GAL4, and transcription will occur
Where do repressors bind to?
Silencer sequences
Where do activators bind to?
Regulatory promoters
What does an insulator do?
block the ability for enhacners to regulate transcription of genes upstream or downstream of it.
When can insulators not block enhancers action?
if the insulator is between an enhancer and a gene
Epigenetics
non-genetic chemical change in the histones or DNA that alter gene function without altering DNA sequence; study of inheritance of traits not coded by DNA sequence
H1 histone
works like a lock for the nucleosome, holding the DNA tightly wrapped around the histone when cytosine is methylated
DNase I sensitivity
Active transcription is occurring due to DNA being open
Nucleosome repositioning
Use of an enzyme (requiring ATP) chromatin remodeling complex pushing a nucleosome up and down the “thread” of DNA, wrapping a different portion of DNA around the histone.
- exposes new area of DNA for transcription
Chemical modification of histones, histone acetylation or methylation and DNA methylation.
8 histones that DNA is wrapped around each have histone tails, which can be targets for binding to trigger conformational changes.
Each one usually has lysine (K) and arginine (R) amino acids. Best understood ones are in lysine.
Modifications can come in the form of methyl - monomethyl, trimethyl, or in acetyl groups. This effects the ability of DNA to bind to the histones.
Acetylation
Open chromatin
Methylation that causes euchromatin (open) are
H3K4me2/3a and H3K36me3
Methylation causing constitutive heterochromatin (closed and stays closed) are
H3K9me3 and H4K20me3
Methylation causing facultative heterochromatin (closed and can switch to open) are
H3K27me3
HAT
histone acetyltransferase: adds acetyl. Put a hat on.
HDAC
histone deacetylase: removes acetyl. De-hat.
FLD produces
deacetylase enzyme, which deacetylases FLC, causing it to “close” and become inactive.
Repression of FLC expression can occur via
deacetylation, which means FLC is facultative, since it can be switched “open” and “closed”
Addition of methyl groups on the histone tails via
HMAT (histone methyltransferase)
