Flashcards in Chromatin Regulation Deck (30):
What is epigenetic inheritance?
Changes in the phenotype that is inherited because of changes in the protein structure (nucleosomes) being covalently modified
What is heterochromatin?
a condensed form of chromatin that is highly resistant to gene expression
what is euchromatin?
a less condensed form of chromatin that is gene expressed
Where is heterochromatin mostly concentrated at
at the centromeres and telomeres
What percentage of the genome is packaged as heterochromatin?
What are position effects?
they are when a gene is silenced because of it is near a heterochromatin
What are barrier DNA?
they are DNA that is between the heterochromatin and euchromatin not allowing the heterochromatin to spread to the adjacent euchromatin
What is position effect variegation?
When heterochromatin is moved closer to euchromatin early in some cells development. this causes the gene to be expressed in in variation.
EXample: the fly eye is both red and white spots because of migration of heterochromatin moving close to the white gene
What are the groups that are covalently linked to the N terminus lysine groups on the histones?
Acetyl - acetylation
Methyl - mono,di,tri methylation
What are the groups that are covalently linked to the N terminus tails of the serine groups on the histones?
phosphate - phosphorylation
What are Histone acetyl transferases (HATs) ?
enzymes that transfer the acetyl groups to the lysine side chains of histones
What are Histone deacetylase complex (HDACs)?
enzymes that remove the acetyl group from the lysine side chain
What are methyl transferases and demethylases?
methyl transferases - enzymes that add methyl groups to the lysine tail of histones
demethylases- enzymes that remove the methyl groups from lysine
What recruits the enzymes that covalently modify histones?
gene regulation proteins recruit at different times in the cell cycle
the covalent bonds sometimes last long after the gene regulatory proteins have left. the epigenetic expressed gene can be passed on to its progeny.
What does the acetylation of the N terminus tail do?
It loosens chromatin structure, because the acetyl group removes the positive charge of the histone
What is another function of the modified histones?
They attract proteins to chromatin that has been appropriately modified.
the proteins determine how the gene is expressed
chromatin structure determines how a gene is expressed
Which histone is the most highly conserved?
H4, all other histones contain variants
When and where are the major histones synthesized?
They are synthesized during S phase of the cell cycle
They are assembled on daughter helices just behind the replication forks
When are the variant histones synthesized?
they are exchanged through a ATP-dependent chromatin remodeling complex
What is the histone code hypothesis?
modification of histones and their variants lead to telling the cell the state of a chromosome.
code-reader complexes bind and read these modifications to tell the state of the chromatin.
a certain combination elicit a particular biological function
What are the code reader complex?
They are proteins that bind to the N-terminus modified tails to determine the state of the chromatin.
How are the N-terminus tails extended from the nucleosomes?
they extend from nucleosomes even when the chromatin is condensed.
What is a chromatin reader -writer nucleosome complex?
The writer modifies a code on a nucleosome and the reader attaches to the same modification positioning the writer on the adjacent nucleosome.
Tis works as a chain reaction affect modifying many nucleosomes in a row
What is the barrier sequence DNA?
sequences of DNA that blocks the reader-writer complex from spreading to the adjacent chromatin domains.
modifications could tighten or loosen domains that is not needed
What is centric heterochromatin?
tightly packed form of heterochromatin that exist in mitosis and interphase
What does the centric heterochromatin contain?
a centromere-specific variant H3 and other proteins that pack the nucleosomes into a highly dense arrangement to form kinetechores
What are alpha satellite DNA sequences?
They are DNA sequences that are repeated over and over on human centromere sites instead of centromere specific DNA sequence.
They are not needed for the formation of centromeres in humans
What are centromeres in complex organisms defined by?
by an assembly of proteins instead of DNA sequences.
How does the centric heterochromatin folds?
the CENP-A H3 variants, folds to the outside where they bind to kinetechore plates