Lecture 11 Flashcards
In general transcription activators promote RNA polymerase II recruitment, T or F
T
Which residue does enhancer of zeste act on and what type of modification is it
Enhancer of zeste methylates lysine 27
What structures are referred to as the building blocks of chromatin
Nucleosomes
Histone methyltransferases mono, di or trimethylated which amino acids within the histone tails
Lysine and arginine
What are the names of the enzymes that reverse histone acetylation and methylation respectively
Histone deacetylase and histone demethylase
Acetylation and methylation of core histone tails can occur simultaneously, T or F
F – methylation and acetylation are mutually exclusive and are competing modifications
Transcriptional activators recruit ATP-dependant chromatin remodelling enzymes, what four ways can these enzymes act to upregulate gene transcription
Selective histone octamer and whole nucleosome remodelling, selective histone removal and replacement and/or by recruiting code writers and readers
How does methylation and acetylation of histone influence transcription
Acetylation and methylation marks in general create binding sites for transcription factors
Explain the molecular mechanism of X-chromosome inactivation
X-chromosome inactivation involves the synthesis of a non-coding RNA known as Xist from the X-inactivation centre (XIC) on the chromosome destined for inactivation. Xist RNA binds to the X chromosome and acts as a recruitment signal to promote the formation of silent chromatin. This is achieved by recruitment of histone modifying enzymes and other Polycomb Group components and leads to the Histone-3 lysine 27 and H3K9 methylation of core Histones in X chromosome chromatin
What is meant by histone code writers
Histone methyltransferases are histone code writers, they act as an additional code on top of the genetic code i.e. epigenetic to
Explain what is meant by X-chromosome inactivation
X-chromosome inactivation is a process that occurs in mammals and acts as a dose compensation mechanism that equalizes the levels of X-chromosome derived gene products in males and females. One X chromosome copy is silenced in each somatic cell during early development of female embryo
Enhancer of zeste is one enzyme that methylates a lysine residue. What position in the polypeptide chain does it act
EZH2 methylates lysine 27
As well as histones, DNA can also be modified by methylation. When and how does this occur
There is a close functional relationship exists between transcriptionally repressive histone methylation and corresponding DNA methylation on cytosine bases. The addition of methyl groups to cytosine residues is mediated by DNA methyltransferases (DNMTs). Transcriptionally inactive promoters are frequently rich in methylated CpG dinucleotides
Specifically what is the effect of histone acetylation on gene transcription
Acetylation of histones creates binding sites for transcriptional activation factors that contain a bromodomain. Histone Acetylation is associated primarily with transcriptionally active promoter sequences.
Methylation can denote transcriptionally active or inactive genes depending on the loci of the residue. Determine whether methylation of lysine 4, 9, 27 and arginine 17 denote transcriptional activation or repression
Arginine 17 and Lysine 4 – transcriptionally active. Lysine 9 and 27 – transcriptionally inactive
Methylation of core histones creates binding sites for transcriptional repressors that contain what kind of domain
Chromodomain
What ways can transcriptional repressors act to decrease gene transcription
Compete for activator binding sites, prevent bound activators from functioning, keep transcriptional activators and transcription machinery away from the start site and also reverse effects of transcriptional activators by creating dense transcriptionally inert chromatin. Finally, they can also recruit enzymes such as histone demethylases and deacetylases as well as methyltransferases
Epigenetic modifications facilitate stable changes in gene expression which may persist or the life of the cell of organism but are erased in the germ line, T or F
F – whilst the statement is true, epigenetic modifications are transferred to the progeny these cells can then decide whether to remove the epigenetic change
The X-chromosome copy that is silenced is determined by maternal gene expression in the fertilised oocyte, T or F
F - Initial selection of the chromosome for silencing is random
Will genes that are more transcriptionally active show higher or lower levels of acetylation
Higher
Methylation of core histones creates binding sites for transcriptional activators that contain what kind of domain
PHD finger domains
Which type of transcription factors will bind to methylated lysine 4 and arginine 17 residues
Transcriptional activators containing PHD fingers
Which type of transcription factors will bind to methylated lysine 9 and 27 residues
Transcriptional repressors containing chromodomains
What is the key difference between genetic and epigenetic modifications
Genetic alterations occur to the DNA sequence directly and permanently affect gene expression. Epigenetic alterations occur to chromatin structure and act to modulate gene expression. These do not alter the DNA sequence and are reversible
