mcb test 1: histone code and chromatin

heterochromatin

transcriptionally inactive

euchromatin

transcriptionally active

how many DNA coils does a histone hold?

~2.5 coils

why is DNA compacted?

for storage purposes

nucleosome

DNA wrapped around histone complex

a histone unit is:

8 histone protein subunits aggregated together

H3 histone tail

have entry and exit sites for DNA loops and influence the behavior of DNA

groups highly represented in histones:

lysine and DNA

how can lysines be modified?

adding an acetyl group to destabilize

methylation

mono, di and tri that stabilizes DNA-lys and retains positive charge

histone code

refers to how histone mods influence DNA/chromatin structure

H3K9Me

codes for heterochromatin

H3K4MeK9Ac

gene expression euchromatin

H3K27Me

irreversible silencing

polychrome genes are also known as

Hox genes

H3S10P

s-phase

acetylation of histones

destabilizes histone/DNA and neutralizes lysine charge

phosphorylation of histones

destabilizes histones

if a lysine is methylated it cannot be

acetylated

HDAC

histone de acetyl complex

what is HDAC?

writer protein that removes the acetyl group from lysine

histone acetyl-transferase(HAT)

writer protein that adds an acetyl group to the lysine

histone methyl transferase

writer protein that adds a trimethyl group to the lysine

is it possible to demethylate a lysine?

it's impossible to demethylate a lysine

drosophila eyes

expresses white gene so red is inverted and is not expressing white gene so it shows white

why does heterochromatin expansion happen?

due to reader-writer proteins

reader proteins

reads modifications on the histone and is able to recruit writer complex to write new code

writer proteins

interacts with downstream molecules and records the code just read onto downstream histones

what does the regulatory protein do?

identifies genetic loci indicative of heterochromatin and brings in reader/writer complex

barrier protein

binds to locus specified in code to prevent heterochromatin expansion

ATP dependent chromatin remodeling complex

hydrolyzes ATP to remodel chromatin in multiple ways

what can the ATP-dependent chromatin remodeling complex do:

remove and substitute histone octamer subunits and/or remove entire octamers