10.1-10.10 Flashcards
1st level of chromatin organization
involves nucleosomes, forms 10 nm fiber
2nd level of chromatin organization
superhelical coiling of nucleosomes to generate 30 nm fiber
3rd level of chromatin organization
looping of 30 nm fiber to generate 300 nm fiber
- involves interphase matrix proteins
4th level of chromatin organization
for condensing chromosome during prophase
- 700 nm per sister chromatid
- 1400 for entire metaphase chromosome
chromatin
dispersed chromosomes during interphase spread out in nucleus
euchromatin
- lightly stained
- occupies most of nucleus
- less densely packed than mitotic chromosome
heterochromatin
- darkly stained
- similar to chromosome at mitosis
- sometimes aggregate into chromocenter
constitutive heterochromatin
regions that are always heterochromatic
- contain multiple copies of non-transcribed repeats
- low # of genes
- replicate late S phase
- genes translocated here likely inactivated
facultative heterochromatin
euchromatin converted to heterochromatin
events associated with causing condensation of euchromatin to heterochromatin
- reduced acetylation of histones
- increased methylation of histones
- hypermethylation of cytosine bases in DNA
Giemsa stain
used in staining process to generate G-bands
do bands or interbands have a higher GC concentration
interbands
are genes more concentrated in bands or interbands
interbands
is p the short or long arm of a chromosome
short
is q the short or long arm of a chromosome
long
is GC-rich associated with coding or binding/structural
coding
is AT-rich associated with coding or binding/structural
binding/structural
where are telomeres and centromeres composed of
constitutive heterochromatin - 4th level of packing
where is the 4th level of chromatin organization found
heterochromatin and mitotic chromosomes
what is the DNA fiber arranged into
series of loops/domains attached to central proteinaceous matrix
ethidium bromide
carcinogen stain that shows bands of DNA, intercalates between base pairs and generates positive superhelical turns
- enables researchers to see size of loops
MARs (matrix) and SARs (scaffold)
DNA sites attached to proteinaceous structures in interphase nuclei
what are the proteinaceous matrixes useful for
transcription and replication
interphase matrix is associated with what level of packing?
3rd
mitotic scaffold is associated with what level of packing?
4th
are MARs fragments AT or GC rich
70% AT
- attach to interphase matrix and mitotic scaffold
prominent component of chromosome scaffold and mitotic nuclear matrix
topoisomerase II (and I)
topoisomerase II
breaks 2 strands
topoisomerase I
breaks 1 strand
MTOC
microtubules organizing center that exists at poles of cell and on each chromosome at kinetochore
what is good evidence that centromere is essential for segregation of chromosomes into progeny cells
loss of acentric fragments during mitosis/meiosis
what is the kinetochore made of
centromeric-binding protein (attaches to centromere) and microtubule-binding protein (attaches to microtubules)
when are cohesions made
G1
when are cohesions added
S phase
are centromeres or telomeres longer
centromeres
any stretch of DNA capable of centromeric function (CEN) should confer what?
mitotic stability upon a plasmid
centromeres are _____-rich
AT
CEN sequences are essential for construction of what?
yeast and human artificial chromosomes
where are tandem repeats usually found
centromeres and telomeres
true or false: tandem repeats have coding function
false
a satellite DNA
tandem arrays in primates (170 ntp)
general formula for telomeric sequences
C(>1)A/T(1-4)
human telomere repeating unit sequence
3’-CCCTAA-5’
ssDNA G-tail of telomeres
14-16 nucleotides long on GT-rich strand
telomerase
ribonucleoprotein enzyme that carries RNA template with same sequence as CA-rich strand to elongated GT-rich strand
what type of activity does telomerase use
reverse transcriptase
in which direction does telomerase work
synthesizes 5’ to 3’
why does yeast telomerase always need to be working
because it is one cell - loss of telomerase functions results in aging and death
true or false: our telomerase gene is tcr silent, inducing aging
true
true or false: telomerase is active in cancer cells
true
how are the ends of chromosomes stabilized
forming long loop of DNA
how is loop at end of chromosome made
3’ ssDNA end displaces same sequence region upstream, ss region pairs with its homologous strand
