Cell Differentiation Flashcards
Which gene expression control is the biggest ?
Gene transcriptional control are paramount as they ensure that the cell will not synthesize superfluous intermediate.
What is the composition of switching devices ?
- short stretches of DNA of a defined sequence
- gene regulatory proteins that recognize and bind to this DNA
Why do we talk about «enhancers»
The DNA sites to which the gene activator proteins bind is called «enhancers» because their presence enhance the rate of transcription initiation.
Enhancers’ function
To attract, position and modify the initiation complex at the promoter so that the transcription can begin
Repressors’ function
They inhibit or reduce the expression of a specific gene by competing with activators or interacting with the initiation complex.
What are the different actions of the repressor ?
- competitive DNA binding
- masking the activation surface
- direct interaction with the initiation complex
List the different types of gene expression controls
- transcriptional control
- RNA processing control
- RNA transport and localization control
- mRNA degradation control
- translation control
- activity control
Describe the chromatin structure
- 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
Define a chromosome
Each chromosome is composed of a single long linear DNA molecule associated with proteins that fold the DNA into a more compact structure.
Describe the nucleosome
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
Describe histones
DNA folding proteins
Each core histones has an N-terminal amino acid tail which extends out of the DNA-histone core
What is Histone H1 and why is it useful ?
H1 is a protein which binds nucleosomes and the linker DNA, stabilizing the 30 nm chromatin fiber.
Describe heterochromatin
- highly condensed form of chromatin
- highly resistant to gene expression
- especially present in telomeres and centrosomes
- there is constitutive heterochromatin and facultative heterochromatin
Define constitutive heterochromatin
- 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)
Define facultative heterochromatin
- is not a permanent feature
- contains genes that are inactive in some cells or at some periods of the cell cycle
What transformations can undergo N-terminal «histone» tails ?
- phosphorylation
- methylation
- acethylation
All are reversible and have a specific meaning = histone code
Describe the functioning of activators in heterochromatin
Activators promote transcription initiation by changing the chromatin structure of promoters of gene in order to make the DNA more accessible.
How can repressors silence large regions of the genome ?
- recruitment of chromatin remodeling complexes
- if histone acethylation = recruitment of histones deacetylases
- if histone methylation = recruitment of histones methyl transferases
Explain why cell differentiation is possible ?
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.
What are the factors influencing cell differentiation ?
- Pre-existing epigenetic landscape
- Epigenetic dynamics
- Lineage specific gene expression program
Define epigenetic inheritance
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.
Define epigenetic
It the the study of inheritable changes in gene expression that do not alter the DNA sequence.
Why is epigenetic inheritance important ?
In addition to play a role in cell differentiation, epigenetic modifications are also essential for the adaptation to the environnement.
List the environnemental factors that can affect the epigenome
- stress
- nutrition
- toxicants
- pathogens
