lecture 9: control of gene expression in eukaryotes Flashcards
what is cell differentiation?
-cells diverge in structure and function during development. All cells have the same genes, but as they differentiate, they get more and more specialized into a specific cell.
what are the 3 steps to the control of gene expression?
1) pre-transcriptional control: chromatin modification
2) transcriptional control: transcription factors (activators and repressors)
3) post-transcriptional control (only talking about RNA processing in this class)
what are the two ways in which chromatin can be organized?
euchromatin and heterochromatin
what is the difference between euchromatin and heterochromatin?
-heterochromatin: highly condensed, genes cannot be transcribed
-euchroamtin: de-condensed, genes are actively transcribed
what happens during pre-transcriptional control?
1) DNA methylation
-cytosine bases get methylated
-methylated genes are not transcribed
-important for long-term inactivation of genes
2) histone acetylation:
-attachment of an acetyl group
(-COCH3) to histone proteins
-alters conformation of histones
-DNA binds less tightly and transcription factors have easier access to genes
what happens when cytosine bases get methylated?
what happens during transcriptional control?
-eukaryotic RNA polymerase cannot recognize a promoter a promoter without transcription factors
-transcription factors:
-bind to non-coding regions of DNA called control control elements:
.activators: enhance transcription
.inhibitors: inhibit transcription
what do transcription factors bind to?
-non-coding regions of DNA called control elements
what are the 2 different types of transcription factors?
activator: enhances transcription
inhibitor: inhibits transcription
what are the 2 types of control elements?
-proximal
-distal
what is a proximal control element?
-close to or within promoter
what is a distal control element?
-upstream (to the left/before) or downstream (after/to the right) of the promoter
-within the introns
-thousands of nucleotides away from the promoter
what is an enhancer?
group of distal control elements
true or false, DNA in all cells have the same control elements.
true
true or false, all cells have the same transcription factors
false, they’re all different
are transcription factors proteins?
yes
what do control elements do?
make genes express themselves in different ways
what are the steps involved in transcription?
1) activators bind to control elements
2) DNA bends to bring together general transcription factors, mediator proteins, activators and RNA polymerase to promoter (all need to be bound for transcription to happen)
3) transcription is initiated
how are genes coding for the enzymes of the same metabolic pathway organized in eukaryotic genes?
they are on different chromosomes (differs from prokaryotes with operons)
how do control elements help coordinate gene expression?
we want to find a way to turn all the genes coding for the production of the enzymes necessary for a metabolic pathway on/off at the same time. control elements/ transcription factors allow us to do this. all the genes coding for the production of the enzymes required for the same metabolic pathway are on different chromosomes, but they all have the same control elements, therefore they will be turned on by the same activators, at the same time.
what happens during post-transcriptional control?
mRNA processing:
-alternative splicing (one single pre-mRNA can give multiple different mature mRNAS)
-you can have control element within intron
-exons can be removed due to splicing
because of this, the proteins synthesized from the same mRNA strand can differ, which leads to different gene expression.
how is the heat shock response linked to transcription factors?
-heat shock proteins stabilize proteins and prevent them from being denatured (help them fold properly)
-there is a stress to the cell (increase in temperature)
-the same transcription factors turn on all the heat shock protein genes
how is euchromatin formed?
by histone acetylation:
-attachment of an acetyl group (-COCH3) to histone proteins
-alters conformation of histones: DNA binds less tightly and transcription factors have easier access to genes
