KH8 Flashcards
what does the genome of each species of eukaryote consist of
a characteristic number of independent linear DNA molecules
each linear DNA molecules is a
chromosome
what do chromosomes never exist as
naked DNA
what do chromosome always exist as
DNA/protein complex termed chromatin
describe a key feature of chromatin organization
condensation or compaction
DNA molecule in average human chromosome is 5 cm long if stretched out = ~5000 times longer than width of typical cell nucleus
So DNA molecule is highly folded/packed/coiled even in the interphase nucleus
when are chromosomes more tightly folded/packed/coiled
mitotic metaphase (more packed than interphase)
why are chromosomes more tightly packed during mitotic metaphase
to facilitate equal distribution between the 2 daughter cells
describe metaphase
highly condensed for transmission to daughter cells
no DNA replication or transcription
only concerned with getting chromosomes to right place
describe interphase
real functional chromosome
undergoing replication and transcription
where action is
chromatin fiber of chromosome unwinds to a degree (from metaphase to interphase) - never to DNA/simplest chromosome structure
dynamic and controlled
what is chromatin
eukaryotic DNA and associated proteins
how many base pairs of DNA in each chromosome for humans
~50-250 million base pairs
what are topological domains
folded domains with definite boundaries
interact among themselves
what is nucleosome
DNA wrapped around histone octamer
where are giant interphase chromosomes from
polytene chromosomes of the fly (drosophila) salivary galdn
describe polytene chromosomes - why they happen
cellular gigantism driven by DNA ~10 cycles of DNA replication without cell division
duplicates but chromosome does not separate
describe polytene chromosomes - physically
all ~1024 daughter chromatids are in perfect alignment making a giant chromosome with regional differences in chromatin condensation
many parallel chromatids
describe regional differences in chromatin condensation
dark bands = condensed chromatin (topological domains)
light bands = boundary elements
describe interphase chromatin organization
dynamic
polytene chromosome puffs show how chromatin decondensation with transcriptional activation
describe puffs of polytene chromosome
puff up = active transcription regions, open and close
associated with active form of RNA polymerase 2 = active transcription
describe puffs of polytene chromosome - colours
red = pol 2 phosphoCTD = active
green = non phosphorylated = inactive
name parts of metaphase chromosome
sister chromatids
centromere
telomere
chromatid
describe metaphase sister chromatids
identical products of the previous semiconservative replication of a single chromosomal DNA molecule
what do metaphase chromosomes show
karyotype (morphology)
chromosomal complement of the species
what characteristics of chromosomes vary
number
shape
size
species specific and sometimes sex specific