Exam 2: Chromatin and Chromosomes Flashcards
in interphase, DNA is…
decondensed and coiled around protein spools
nucleosome “beads on a string”
protein spool that DNA of eukaryote chromosomes are always spooled around
left handed spiral
eukaryotes only
nucleosome core
roundish disk made of 8 histones
150 base pairs of dsDNA in 2 loops
allows chromosomes to be condensed in length
what proteins are nucleosomes made of
histones (100-200 AAs)
25% lysine and arginine to help bind to acidic phosphates on DNA
each core is wrapped in ____ turns of DNA
~1.7, almost 2
between nucleosomes there is additional ____
unspooled linker DNA
this all forms a repeating unit of roughly 200 bp
150 bp nucleosome DNA and 50 bp linker DNA
each nucleosome core is an ____
octamer
8 histone molecules
if you mix histones together…
they will spontaneously assemble into nucleosome cored
if you mix DNA with nucleosome cores…
the DNA naturally coils around the cores
what happens during s-phase
a ton of nucleosome cores are made
newly replicated DNA wraps around immediately
nucleosomes shorten DNA by a factor of _
7; 3 feet to 5 inches
the nucleosome packing shortens DNA by another 7
total packing is by a factor of 49/50
nucleosomes don’t only stick to DNA…
they stick to each other making disk-like structures
a strand about 30nm called chromatin fiber (next level of supercoiling) involving histone tails
scaffold proteins and loops
central core of skeleton for the chromosome
chromatin fibers form loops and are attached to the scaffold
loops exist in interphase and metaphase chromosomes
matrix associated region
AT-rich regions of DNA attached to scaffold protein
attach bases of DNA loops
MAR=SAR (scaffold associated region)
the final shortening of chromosomes occurs during _____
prophase
highest level of chromatin packing
how do we number the human karyotype
number the autosomes from longest to shortest
divide into groups A-G based on shapes
sex chromosomes are simply X and Y
what is the smallest chromosome
chromosome 21
it’s out of order~
most chromosomes have regions of….
constitutive heterochromatin near the centromeres
large heterochromatic centromeric bands on 1, 9, 16
acrocentric autosomes include…
13, 14, 15, 21, 22
all have ribosomal genes on the short arms
chromatin contains
both DNA and protein
more protein than DNA
nonhistone proteins in chromatin include both
structural and regulatory proteins
differences between euchromatin and heterochromatin
the amount of packing
heterochromatin
more condense, less active, late-replicating, dark staining
constitutive is always hetero
facultative is sometimes hetero
euchromatin
decondensed and active
facultative is sometimes euchromatin
constitutive heterochromatin
always hetero
tails of Y’s, all centromeric regions
especially 1, 9, 16
facultative heterochromatin
goes between hetero and euch
barr body
female’s x chromosome
Giemsa stain
G-bands are alternating light and dark bands on chromosomes when a staining technique is used
bands are large and contain many genes
numbered to ID regions, blocks of genes, deletions
tell chromosomes apart
with careful banding techniques…
recognize same chromosome in diff generations
this is b/c some parts of chromosomes are more variable, esp in heterochromatic regions
if you remove histones from a mitotic chromosome what fraction of the original weight of the chromosome does this remove?
50%
1/3 remaining mass is other proteins including scaffolds
resulting structure is loose, relaxed DNA still attached in large loops to the scaffold
