lecture 9: control of gene expression in eukaryotes

Question 1

what is cell differentiation?

Answer 1

-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.

Question 2

what are the 3 steps to the control of gene expression?

Answer 2

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)

Question 3

what are the two ways in which chromatin can be organized?

Answer 3

euchromatin and heterochromatin

Question 4

what is the difference between euchromatin and heterochromatin?

Answer 4

-heterochromatin: highly condensed, genes cannot be transcribed
-euchroamtin: de-condensed, genes are actively transcribed

Question 5

what happens during pre-transcriptional control?

Answer 5

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

Question 6

what happens when cytosine bases get methylated?

Answer 6

Question 7

what happens during transcriptional control?

Answer 7

-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

Question 8

what do transcription factors bind to?

Answer 8

-non-coding regions of DNA called control elements

Question 9

what are the 2 different types of transcription factors?

Answer 9

activator: enhances transcription
inhibitor: inhibits transcription

Question 10

what are the 2 types of control elements?

Answer 10

-proximal
-distal

Question 11

what is a proximal control element?

Answer 11

-close to or within promoter

Question 12

what is a distal control element?

Answer 12

-upstream (to the left/before) or downstream (after/to the right) of the promoter
-within the introns
-thousands of nucleotides away from the promoter

Question 13

what is an enhancer?

Answer 13

group of distal control elements

Question 14

true or false, DNA in all cells have the same control elements.

Answer 14

true

Question 15

true or false, all cells have the same transcription factors

Answer 15

false, they’re all different

Question 16

are transcription factors proteins?

Answer 16

yes

Question 17

what do control elements do?

Answer 17

make genes express themselves in different ways

Question 18

what are the steps involved in transcription?

Answer 18

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

Question 19

how are genes coding for the enzymes of the same metabolic pathway organized in eukaryotic genes?

Answer 19

they are on different chromosomes (differs from prokaryotes with operons)

Question 20

how do control elements help coordinate gene expression?

Answer 20

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.

Question 21

what happens during post-transcriptional control?

Answer 21

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.

Question 22

how is the heat shock response linked to transcription factors?

Answer 22

-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

Question 23

how is euchromatin formed?

Answer 23

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