lec 25 DNA organization Flashcards
what are chromatins?
a mixture of DNA and histone proteins that form the chromosome
what are nucleosomes made of?
made of histone cores and linker DNA
what structure do nucleosomes form in chromatin?
a “bead-on-a-string” structure
what are histones?
proteins that package into nucleosomes
what are histones made of?
they are 25% lysine and arginine which are positively charged to neutralize the negatively charged DNA
what are the 5 types of histones?
H1, H2A, H2B, H3, and H4
why are histone tails sticky?
because when the histone tail is positively charged, it is deacetylated/condensation which makes it sticky, when it is neutral or negatively charged it is acetylated/decondensation, they want to be sticky to attach to DNA
what do histone tails do?
they help pack nucleosomes into 30nm fiber
what do condensed 30nm fibers make?
chromosomes
what part of a 30nm fiber is more active for transcription
the less well ordered regions
what enzymes alter the accessibility of DNA to proteins?
HATs and HDACs
what are telomeres?
the ends of DNA that prevent degredation
what enzyme prevents shortening by extending the telomeres?
telomerase
what enzyme digests overhang if not repaired by telomerase?
exonuclease
what stops the exonuclease from accessing chromosomes?
T-loops
