Flashcards in Lecture 5 Slides Deck (55):
Nuclear envelope made up of
Outer and inner nuclear membranes
Where is nuclear lamina? What binds to it?
On inside of inner nuclear membrane. Peripheral heterochromatin binds to it.
What is a continuation of the outer nuclear membrane
What is a chromosome. What does it do?
A single DNA molecule.
Maintain genetic info
Replicate genetic info
Segregate genetic info
What is chromatin made of
How many histones in nucleosome
What links Nucleosomes? What is length between them?
200 nucleotide pairs of FNA
What does nuclease do
Digest linker DNA
What is the diameter of a nucleosome
How many times does DNA wrap around nucleosome core
How is DNA coiled in Nucleosomes
How big are histones? How are thy structured?
Histone fold at C terminus
What is the charge of histones
What are histones enriched in? What is their PI?
Enriched in arginine and lysine. pIs range from 9.8 to 10.25
How foes histone bind to DNA
Via various noncovalent bonds
What extends from nucleosome. What does it have?
Amino-terminal tails. Have numerous covalent modifications.
What encodes histones
Multigene families expressed during DNA replication
Are histones found in bacteria
No, but in archaea yes
Are histones present in all eukaryotes
All but dinoflagellates
What do archaea histone-like proteins assemble
Tetramers that protect ~60bp of DNA from nuclease digestion
How is chromatin remodeled
ATP-dependent DNA translocate a anchor on histone October and move DNA around the nucleosome
What is the function of chromatin remodeling complexes
-work with histone chaperones to remove and replace histones
-assemble Nucleosomes on newly-replicates DNA
-assist in DNA repair
-condense chromatin to form heterochromatin
-regulate gene expression by altering chromatin structure at promoters
-modify transcription elongation
Has same ionic conditions as inside cell
How is 30nm fiber extracted from cells
Using isotonic buffers
How are Nucleosomes stacked
In 30 nm fibers
What are 30 nm fibers formed by
Interaction of histone tails
Linker histone H1 (1 per nucleosome)
Qualities of epigenetic inheritance
Phenotypes not based on changes in DNA sequence
Genes may lie within different chromatin structures:
-euchromatic or heterochromatin
Less condensed, active in gene expression
Highly condensed, gene expression repressed
What happens to gene expression if structural gene is not barred from heterochromatin
Structural gene may be inactivated
Result of chromosome rearrangement
Allows heterochromatin to spread into structural gene
Result of acetylation of lysine on N terminal (histone) tails
Loosens chromatin structure
What does acetyl group do to lysine
Removes its positive charge and reduced the affinity of the tails for adjacent Nucleosomes
Histone acetyl transferase
Adds acetyl group to lysine
Removes acetyl group from lysine
Lysine methyl transferase and demethylase
Add and remove methyl groups to lysine, respectively
Arginine methyl transferase
Adds methyl group to arginine
What does serine phosphorylation do to a histone
Gives it a negative charge
Types of histone modifications
Code "reader or effector"
Enzyme that adds a modification
Enzyme that removes a modification
Code "reader or effector"
Enzyme that recognizes the modification and translates it into a specific outcome
Which trimethylations are associated with transcriptional repression
H3K9, H3K27, and H4K20. Enriched in heterochromatin.
Which methylations are associated with transcriptional activation
H3K4, H3K36, H3K79. Enriched in euchromatic
Histone methyl transferase. h3K4Me. Over expression resulting from gene fusions in hematopoietic stem cells are associated with leukemia
Invites other molecules to come and bind? Positive feedback loop and self propagating. Changes both chromosomes.
Affects only one chromosomal copy. Depends on transcription regulators synthesized in cytosol.
To loosen chromatin, you need an acetyl group. To tighten then you need
A methyl group or more
How does histone deacetylase propagate heterochromatin?
Removes acetyl group from H3 tail lysine 9 so that histone methyl transferase can methyl H3K9
How does HP1 chromo domain work
It is a reader. It reads the histone code. Binds H3K9Me3
What does Chromatin remodeling complex do to promote heterochromatin
It is ATP dependent. Uses ATP to shift DNA on Nucleosomes
How is heterochromatin structure stabilized
Oligomerization of HP1
What is loss of HP1 associated with
To identify DNA sequence to which a modified histone or regulatory protein will bind