Chapter Thirteen: The Eukaryotic Chromosome Flashcards
all cells have ___ nuclear DNA, but cells are ___ from one another
identical
different
chromosomes support the ___, ___, ___, and ___ of genetic information
packaging, replication, segregation, and expression
generic term for any complex of DNA and protein found in the nucleus of a cell
chromatin
chromosomes are separate pieces of ___ that behave as a unit during ___
chromatin
cell division
chromatin is made up of roughly ___, ___, ___, and ___
1/3 DNA, 1/3 histones, 1/3 nonhistone proteins, and significant amounts of RNA
DNA interaction with histones and nonhistone proteins produces a significant level of ___ to fit into a cell nucleus
compaction
histones are ___ proteins that are ___ charged and highly ___
small
positively
conserved
what does it mean for something to be conserved
the same throughout all life, serve the same purpose
histones function to ___ and ___ DNA
bind to and neutralize
five types of histones
H1, H2A, H2B, H3, and H4
H1-H4, make up the nucleosome, most rudimentary packaging unit
core histones
thousands of proteins that make up chromatin and are not histones
nonhistone proteins
are there more histone or nonhistone proteins
nonhistone
four functions of nonhistone proteins
- structural role
- chromosome replication
- chromosome segregation
- active in transport
when chromosomes are treated with ___, you can see the scaffolding of nonhistone proteins
detergent
help move chromosomes along the spindle apparatus, a nonhistone protein
kinetochore proteins
blue stain used in the nucleus
DAPI
when stretched out, the DNA in a single cell would be about ___
6 feet long
___ allows DNA to fit into a cell nucleus
compaction
structures formed by winding of DNA around histones, resemble beads on a string
nucleosome
nucleosome are the fundamental unit of ___
chromosomal packaging
___ and ___ of nucleosomes affect genetic function
spacing and structure
nucleosome ___ is highly defined and varies in different cell types and under different conditions
arrangement along chromatin
nucleosome core is an octamer of ___, contains histones ___
two
H2A, H2B, H3, H4
about ___ of DNA wrap twice around core of eight histones
160 bp
histone ___ is associated with linker DNA as it enters and leaves the nucleosome core
H1
DNA ___ as it wraps around the core histone octamer
bends sharply
___ dictates preferred nucleosome positions along the DNA
base sequence
chromosomal DNA appears as ____ of chromosome in electron micrographs
long loops anchored to scaffold backbone
protein complexes that form loops of DNA
condensins
___ protein subunits constitute condensins
five
condensins exist as ___ that form around the ___
rings
nucleosome
a model of higher-order chromosome packaging
nucleosome supercoiling
banding patterns in a karyotype reflect how ___ the DNA is
condensed
banding patterns on each chromosome are highly ___
reproduceable
diagrams of G-banding patterns
idiograms
short arm of a chromosome
P arm
long arm of a chromosome
Q arm
within each arm, light and dark bands are ___
numbered consecutively
a physical mapping approach where fluorescent tags are used to detect hybridization of nuclei acid probes with chromosomes
fluorescent in situ hybridization (FISH)
FISH allows the locating of ___ within a chromosome
specific DNA sequences
three general steps of FISH
- chromosomes are spread on a glass slide and denatured to make them single stranded
- a DNA sequence is labeled with a fluorescent tag to make a probe
- the probe hybridizes to chromosomes at complementary regions
how would you find the sequence ATCCGATC within a chromosome
fluorescent tag of complementary base sequences (TAGGCTAG)
a variation of FISH that has chromosome-specific probes each labeled with a different fluorescent dye
special karyotyping (SKY)
highly condensed form of chromatin, usually transcriptionally inactive
heterochromatin
heterochromatin is the ___ stained regions of the chromosome
darkly
heterochromatin that is condensed in all cells
constitutive
example of constitutive heterochromatin
most of the Y chromosome
heterochromatin that is condensed only in some cells and relaxed in other cells
facultative heterochromatin
example of relaxed heterochromatin
X chromosome in female mammals
chromatin that is relaxed, usually transcriptionally active
euchromatin
euchromatin is the ___ stained regions of chromosomes
lightly
transcription requires changes in chromatin ___
structure
promoters of inactive genes are hidden in ___
nucleosomes
to activate a gene, ___ bind to enhancers and recruit ___ proteins
transcription factors
chromatin remodeling
promoters are exposed by ___ or ___ nucleosomes
removing or repositioning
variable expression of a gene in a population of cells, caused by the gene’s location near highly compacted heterochromatin
position effect variegation (PEV)
the gene for white+ eyes in drosophila is normally located in ___
euchromatin
chromosomal inversion can result in the w+ gene being located adjacent to ___
heterochromatin
heterochromatin can ___ adjacent genes
turn off
___ can be caused by spreading of heterochromatin into nearby genes
spreading
spreading of heterochromatin can occur over ___ of chromatin
> 1000kb
in drosophila the w+ gene expresses a ___ phenotype; if the w+ gene is silenced, a ___ phenotype is expressed
red
white
mutations in drosophila that enhanced heterochromatin formation made eyes ___
more white
mutations in drosophila that suppressed heterochromatin formation made eyes ___
less white
DNA segments that block the spread of heterochromatin
barrier elements
extend out from the nucleosome and are platforms for modifications
histone tails
the four core histone tails can be modified with ___
chemical groups
extend out from the nucleosome and are platforms for modifications
histone tails
___ can add chemical groups to histone tails
enzymes
the modification of histone tails is a method of ___
differentiation between organisms with identical DNA
modified histone tails can alter ___ and bind ___
nucleosomes
chromatin modifier proteins
histone tail modification alter ___ structure
chromatin
adds acetyl groups to histone tails
histone acetyltransferase
acetylation prevents ___ of nucleosomes
close packaging
acetylation favors ___ of genes in ___
expression
euchromatin
removes acetyl groups from histone tails
histone deacetylase
adds methyl groups to histone tails
histone methyltransferase
the effect of histone tail methylation depends on which ___ is modified
amino acid
methylation of H3 lysine 9 favors ___ formation
heterochromatin
removes methyl groups from histone tails
histone demethylase
X chromosome inactivation in female mammals occurs through ___
heterochromatin formation
Barr bodies are an example of ___
facultative heterochromatin
random X inactivation occurs about ___ after fertilization
2 weeks
some cells have ___ X inactivated, some have ___ X inactivated; all cells descendants will have ___ X inactivated
maternal
paternal
the same
X-inactivation is initiation by the expression of the ___
Xist gene
Xist stands for ___
X inactivation specific transcript
the xist gene is expressed in the ___ X chromosome but not on the ___ X chromosome
inactive
active
Xist RNA is a ___, ___, ___-acting, ___ RNA
large, noncoding, cis-acting, regulatory
Xist RNA binds to the X chromosome that it was ___, then initiates ___ that result in ___
expressed from
histone modifications
heterochromatin formation
rate of DNA synthesis in human cells is about ___
50nt/sec
accessible regions of DNA that are devoid of nucleosomes
origin of replication
it would take ___ to replicate the human genome If there was only one origin of replication
800 hours
s phase lasts about ___
8 hours
most mammalian cells have about ___ origins of replication
10,000
many origins are ___
active at the same time
accessible regions of DNA that are devoid of nucleosomes
origin of replication
DNA being replicated in both directions from one origin
replication unit / replicon
nucleosomes are ___ and ___ during DNA replication
disassembled and reformed
DNA is packaged in nucleosomes within ___ of synthesis
minutes
new nucleosomes are composed of ___ and ___
recycled histones and new histones
chromatin is open to ___ just after replication
histone modification
“caps” that protect the ends of eukaryotic chromosomes
telomeres
telomeres consist of ___, do not contain ___
specific repetitive sequences
genes
telomere sequence in humans is ___; telomere sequence in tetrahymena
TTAGGG
TTGGGG
telomeres prevent ___ and maintain ___
chromosome fusion
integrity of chromosomal ends
for replication at the end of chromosomes, RNA primers are ___, which leaves a length of DNA ___ at the 5’ ends
removed
missing
without a special mechanism, DNA would be ___ from every new DNA strand every cell cycle
lost
a ribonucleoprotein that extends telomeres
telomerase
___ is complementary to telomere repeated sequences and serves as a template for addition of new DNA to telomeres
telomerase RNA
additional rounds of telomere elongation occur after telomerase ___
translocates to newly-synthesized end
in humans, the levels of telomerase and cellular life span ___ between different types of cells
varies
most somatic cells have ___ expression of telomerase
low
somatic telomeres ___ at each cell division, senescence after ___ generations in culture
shorten
<50
germ cells, stem cells, and tumor cells have ___ expression of telomerase; telomeres ___ at each cell division
high
maintain length
proteins that bind to telomeres and fold the DNA
shelterin
shelterins function to protect against ___ and ___
degradation by nucleases and non-homologous end joining (NHEJ)
segregation of condensed chromosome depends on ___
centromeres
during anaphase of mitosis and meiosis II, ___ must segregate to different daughter cells
sister chromatids
during anaphase of meiosis I, ___ do not separate but ___ segregate to different cells
sister chromatids
homologous chromosomes
two functions of centromeres
hold sister chromatids together
attachment sites for chromosome segregation machinery
protein that holds sister chromatids together
cohesin
specialized structure of DNA and protein at the centromere where chromosomes attach to spindle fibers
kinetochore
yeast centromeres are two conserved ___ DNA sequences separated by ___
10-15bp
90bp
proteins bind to DNA in a ___ fashion
sequence-dependent
centromeres of higher eukaryotes are ___ and ___
larger and more complex
centromeres of higher eukaryotes consist of ___ of ___
tandem repeats of noncoding satellite DNA
kinetochores assemble at ___ and are the site of attachment for ___
centromeres
spindle fibers
chromatin is ___ at the centromere
packaged differently
at the centromere, H3 is replaced by the histone variant ___
CENP-A
CENP-A is a nucleosome that acts as ___ for kinetochore proteins
scaffolds
protein complex that holds sister chromatids together during metaphase
cohesin
at anaphase of mitosis, cohesin is ___ and sister chromatids are ___
enzymatically cleaved
released from each other
at anaphase I of meiosis, cohesin along ___ is enzymatically cleaved but cohesin at ___ is not enzymatically cleaved
chromosome arms
centromeres
in anaphase I, mitotic-specific subunit interacts with the protein ___ which protects cohesin from degradation
shugoshin
after entry into metaphase II, ___ is removed and ___ is degraded
shugoshin
centromeric cohesin
artificial chromosomes require these three key elements
- centromeres
- telomeres
- origins of replication
without a centromere, there are ___
segregation errors
without a telomere, there are ___
degradation errors if linear
yeast fused chromosome consists of giant ___ fusion of all ___ normal yeast chromosomes
11.8Mb
16
synthetic chromosomes ___ from artificial chromosomes
differ
DNA in synthetic chromosomes is ___
entirely man made
DNA in artificial chromosomes is ___
pieced together from yeast chromosomes
synthetic chromosomes include ___ on corresponding yeast chromosome
all genes present
artificial vectors usually have a ___yeast gene
single protein-coding
fused and synthetic chromosomes help study ___ that support life
minimal genome components
