Epigenetics Flashcards
What is epigenetics ?
The study of the effects of reversible chemical modifications to DNA and/or histones on the pattern of gene expression.
True or false : Epigenetic modifications alter the nucleotide sequence of DNA
False
What’s the epignome ?
Specific pattern of epigenetic modifications present in a cell at a given period of time
True or false : during its lifespan, an organism will have multiple epigenomes
True
How can we explain that individuals with the same genotype can have different phenotypes ?
Because the phenotype results from the interaction between the genome and the epigenome
True or false : epigenetic modifications can be heritable, independently from the DNA sequence
True
Name example of environmental factors that can cause epigenetic modifications
- Diet
- Stress
- Chemicals
- Toxins
Name what epigenetic modifications can affect
- Reproduction
- Development
- Disease processes
- Adaptation to the environment
- Behavior
Name the 3 types of epigenetic modifications
- Reversible modifications of DNA by the addition or removal of methyl groups
- Chromatin remodeling by the addition or removal of chemical groups to histone proteins
- Regulation of gene expression by noncoding RNAs
Describe DNA methylation
In mammals, after DNA replication and during cell differentiation :
- A DNA methyltransferase (DNMT) adds a methyl group to a cytosine adjacent to a guanine (CpG islands)
- Blocking the binding of transcription factors or RNApol
- Gene is silenced
Where does much of the DNA methylation occur ?
Repetitive DNA sequences
–> silencing LINE and SINE repetitive sequences (TEs)
What is a Housekeeping gene ?
Constitutive gene (transcribed continually) to maintain basic cellular functions
–>** they are hypomethylated**
Name examples of tissues where there is a lot of housekeeping genes
- Bonne marrow (for general/white blood cell activation, immune response)
- Arteries (for angiogenesis)
- Bladder (for muscle contraction, excretion, secretion)
Name the processes used for regulation of the chromatin structure
- Chromatin remodeling (going back and forth between eurochormatin anad heterochromatin)
- Histone modifications (acetylation, methylation)
What is the purpose of histone acetylation?
Increases the availability of DNA to the transcription machinery (loose/eurochromatin)
How does histone acetylation occur ?
A histone acetyl transferase (HAT) adds an acetyl to a lysine
- a histone deacetylase (HDAC) removes it
What is the purpose of histone methylation ?
Inhibits or activates transcription
What determines the effect of histone methylation on transcription ?
The lysine that is methylated:
H3K4me3 = inhibits transcription
H3K9me3 = activates trancription
What are writers and erasers
They modify histones
Writers = protein methyltransferases and histone acetyltransferases
Erasers = histone deacetylases and lysine demethylases
What do readers do?
They further modify chromatin structure/regulate transcription by :
- Recognizing epigenetic marks
- Recruiting other proteins
- Modulating chromatin structure (eurochormatin to heterochromatin vice versa)
What is Histone code ?
Hypothesis stating that transcription of genetic information is partly regulated by histone modifications and their interactions
How can epigenetic changes be inherited ?
by inheriting the acetylation and/or methylation patterns
Why do we say that methylation marks are temporary ?
Because those patterns are often reset during the formation of gametes (close to 100% reprogramming)
Define epigenetic inheritance
Inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence of a genome
