Cell Differentiation

Question 1

Which gene expression control is the biggest ?

Answer 1

Gene transcriptional control are paramount as they ensure that the cell will not synthesize superfluous intermediate.

Question 2

What is the composition of switching devices ?

Answer 2

• short stretches of DNA of a defined sequence

- gene regulatory proteins that recognize and bind to this DNA

Question 3

Why do we talk about «enhancers»

Answer 3

The DNA sites to which the gene activator proteins bind is called «enhancers» because their presence enhance the rate of transcription initiation.

Question 4

Enhancers’ function

Answer 4

To attract, position and modify the initiation complex at the promoter so that the transcription can begin

Question 5

Repressors’ function

Answer 5

They inhibit or reduce the expression of a specific gene by competing with activators or interacting with the initiation complex.

Question 6

What are the different actions of the repressor ?

Answer 6

• competitive DNA binding
• masking the activation surface
• direct interaction with the initiation complex

Question 7

List the different types of gene expression controls

Answer 7

• transcriptional control
• RNA processing control
• RNA transport and localization control
• mRNA degradation control
• translation control
• activity control

Question 8

Describe the chromatin structure

Answer 8

• 3,2 X 10 expo 9 nucleotides
• distributed over 24 chromosomes
• DNA + folding proteins = chromatin
• chromatin is in the form of fiber with a diameter of about 30 nm

Question 9

Define a chromosome

Answer 9

Each chromosome is composed of a single long linear DNA molecule associated with proteins that fold the DNA into a more compact structure.

Question 10

Describe the nucleosome

Answer 10

It is the most basic level of packaging.
A nucleosome bead is composed of 8 histones and 146 base pairs of DNA
The formation of nucleosomes converts a DNA molecule into a chromatin thread about one third of its initial length

Question 11

Describe histones

Answer 11

DNA folding proteins

Each core histones has an N-terminal amino acid tail which extends out of the DNA-histone core

Question 12

What is Histone H1 and why is it useful ?

Answer 12

H1 is a protein which binds nucleosomes and the linker DNA, stabilizing the 30 nm chromatin fiber.

Question 13

Describe heterochromatin

Answer 13

• highly condensed form of chromatin
• highly resistant to gene expression
• especially present in telomeres and centrosomes
• there is constitutive heterochromatin and facultative heterochromatin

Question 14

Define constitutive heterochromatin

Answer 14

• is a permanent feature of a chromosome
• often doesn’t contain genes
• found in centromeres, telomeres and other region of the chromosomes (most of the Y chromosome)

Question 15

Define facultative heterochromatin

Answer 15

• is not a permanent feature

- contains genes that are inactive in some cells or at some periods of the cell cycle

Question 16

What transformations can undergo N-terminal «histone» tails ?

Answer 16

• phosphorylation
• methylation
• acethylation

All are reversible and have a specific meaning = histone code

Question 17

Describe the functioning of activators in heterochromatin

Answer 17

Activators promote transcription initiation by changing the chromatin structure of promoters of gene in order to make the DNA more accessible.

Question 18

How can repressors silence large regions of the genome ?

Answer 18

• recruitment of chromatin remodeling complexes
• if histone acethylation = recruitment of histones deacetylases
• if histone methylation = recruitment of histones methyl transferases

Question 19

Explain why cell differentiation is possible ?

Answer 19

Dynamic changes in chromatin structure enable the binding of multiple TFs to trigger the specific transcriptional programs and to drive gene expression, thus, cell differentiation.

Question 20

What are the factors influencing cell differentiation ?

Answer 20

• Pre-existing epigenetic landscape
• Epigenetic dynamics
• Lineage specific gene expression program

Question 21

Define epigenetic inheritance

Answer 21

Once a cell in a multicellular organism differentiate into a specific cell type, it maintains its choice through many subsequent cell generations.
It remembers the changes in gene expression involved in the choice.
This phenomenon of cell memory is a prerequisite for the creation of organized tissues and for the maintenance of stably differentiated cell type.

Question 22

Define epigenetic

Answer 22

It the the study of inheritable changes in gene expression that do not alter the DNA sequence.

Question 23

Why is epigenetic inheritance important ?

Answer 23

In addition to play a role in cell differentiation, epigenetic modifications are also essential for the adaptation to the environnement.

Question 24

List the environnemental factors that can affect the epigenome

Answer 24

• stress
• nutrition
• toxicants
• pathogens