Oct 2 Flashcards
What is used to convert 10 nm to 30 nm DNA?
Histone H1
What compacts 30 nm DNA even further, which protein holds the base of the loop, why does it help?
The 30 nm DNA forms loops om a chromosome scaffold. Topoisomerase 2 holds the base of the loop, keeps the loops isolated, allows chromatin to be even more compact
What forms loop regions together in the DNA strand following duplication (interphase)?
Cohesin
What does topoisomerase 2 do during inter phase?
It will cut dsDNA, those strands form knots with the loops, introduces entanglement.
When does topoisomerase 2 induce entanglement and relax DNA?
It induces entanglment in S phase (part of interphase). It relaxes DNA during transcription.
What helps correct for knots made by topoisomerase during interphase?
Condensin
What are the two histone variants, what do they replace?
H2A.X is a phosphorylated version, found where there are dsDNA breaks, so recognized by DNA repair enzymes.
CENP-A replaces H3 subunits in centromeric nucleosomes, kinetochore proteins (binding sites for spindle fibers) bind to CENP-A
What is used instead of histones as sperm nuclei are so small that DNA must be even more compact than normal even though there is only 1 copy of each chromosomes
Protamine is used, it has lots of Arg+
Does protamine protect DNA from digestion enzymes?
No, none of it is protected. DNA around the histone core itself will be protected
What are the 3 ways that nuclosome remodeling complexes move nucleosomes?
Sliding, ejection, or do a dimer exhange so the DNA binds less tightly to histone core
How do proteins restrict or encourage nucleosome formation at certain spots?
If 2 proteins have less than 150 BPs between them, then a histone can’t bind there and use that DNA to wrap around it.
A protein can also bind and bind the the nucleosome facilitating nucleosome assembly
Why do the minor grooves of DNA have more AT than GC for histone binding?
AT has 2 H bonds not 3, so it is more flexible and can bend around histone core more easily
