CHAPTER 12: The Eukaryotic Chromosome
a YAC that can replicate within the cell but will not segregate properly contains a(n) __________ but is missing a(n) __________
ARS; centromere
an important feature of an autonomously replicating sequences (ARS) is a(n) __________ that binds to enzymes that initiate DNA replication
AT-rich consensus sequence
barrier elements
DNA elements that block the spread of heterochromatin.
the nucleosome core includes two each of four histones named...
H2A, H2B, H3 and H4
in regions of heterochromatin, methylation of the lysine at position 9 (K9) is observed for histone
H3
the template used for adding new repeating units to telomeres is found in the...
RNA component of telomerase
in somatic cells of human females one of the two X chromosomes is randomly turned off. What is this mechanism called?
X-chromosome inactivation
in order to facilitate chromosome inactivation, Xist RNA coats the ______ chromosome and recruits _______ modifying enzymes
X; histone
the 450kb region on the X chromosome that plays an important role in X chromosome inactivation is the...
XIC
synthetic chromosome
a chromosome whose DNA component is made using a DNA synthesis machine.
what is an artificial chromosome?
a cloning vector that can accept large DNA inserts and be passed on like a chromosome in a living cell
nucleosome (nucleolus)
a large, spherical organelle visible in the nucleus of interphase eukaryotic cells with a light microscope; the site of ribosome biosynthesis.
level of chromatic compaction of nucleosome cause what type of condensation
segments of DNA are wound around histone cores
as the size of the insert increases in YAC vectors, chromosome _________ becomes more accurate
segregation
fxn. of TRP+ in the YAC vector
selectable marker
'p' portion of the chromosome is the...
short arm of the chromosome
which types of sequences can be found within constitutive heterochromatin: protein-coding genes transcribed in most cells simple repetitive sequences (SSRs) transposable elements transcritptionally-active sequences
simple repetitive sequences (SSRs) transposable elements
telomeres
specialized terminal structures on eukaryotic chromosomes that ensure the maintenance and accurate replication of the two ends of each linear chromosome.
a variation of the FISH technique that uses probes labeled with specific mixes of fluorescent dyes to give each of the 24 human chromosomes a different color is called
spectral karyotyping (SKY)
spectral karyotyping (SKY) is a method for...
staining each type of human chromosome with a different color using fluorescently labeled probes
telomere
structure at the end of a linear chromosome
level of chromatic compaction of 300 angstroms fiber cause what type of condensation
supercoiling of nucleosomes
enzyme that restores sequences which extend the ends of chromosomes is called
telomerase
the structures found at both ends of eukaryotic chromosome are called...
telomeres
replicon (replication unit)
the DNA running both ways from one origin of replication to the endpoints where it merges with DNA from adjoining replication forks.
Chromatin
the complexes of DNA and protein found in a cell's nucleus that form chromosomes.
histone proteins can be chemically modified by adding acetyl or methyl groups to ___________ which extend outward from the nucleosome
their N-terminal tails
euchromatin
a loosely condensed chromosomal region in which many genes are transcriptionally active.
condensins
a multisubunit complex of proteins in eukaryotic cells that compacts chromosomes during mitosis.
the Xist gene produces ..., leading to inactivation
a noncoding RNA that coats the X chromosome
fluorescent in situ hybridization (FISH)
a physical mapping approach where fluorescent tags are used to detect hybridization of nucleic acid probes with chromosomes.
shelterin
a protein complex that binds to telomeres and protects them from enzymatic activities (ie. degradation).
X inactivation center (XIC)
a region of the X chromosome (~450 kb) that mediates dosage compensation.
noncoding RNA (ncRNA)
a transcript that lacks an open reading frame and functions as an RNA molecule.
spectral karyotyping (SKY)
a type of fluorescent in situ hybridization that results in labeling of each of the 24 human chromosomes as a different color.
immediately after it is synthesized, a synthetic yeast chromosome contains...
all of the genes present on the corresponding yeast chromosome
fxn. of centromeres in the YAC vector
allows for proper chromosome segregation
G bands
alternating dark and light segments (1-10 Mb) of a chromosome after staining with Giemsa dye.
telomerase
an enzyme crucial to the successful replication of telomeres at chromosome ends.
histone deacetylase
an enzyme that removes acetyl groups from histone proteins
a cloning vector that can accommodate a large DNA insert and behave like a chromosome when it is inside a living cell is called a(n)
artificial chromosome
in yeast cells, an 11-base pair AT-rich sequence that binds to enzymes that initiate replication is found in a(n)....
autonomously replicating sequences (ARS)
in newly formed nucleosomes, the histones may...
be unmodified initially but are accessible to modifying enzymes that can restore the parental chromatin structure
types of cells that show high levels of telomerase activity
cancer cells, stem cells involved in forming new RBCs, germ-line cells involved in gametogenesis
nonhistone chromosomal proteins
chromatin constituents other than histones with a wide variety of functions.
constitutive heterochromatin
chromosomal regions that remain condensed in heterochromatin at most times in all cells.
centromere
chromosome location where kinetochore forms
fxn. of foreign DNA in the YAC vector
cloned DNA to be transferred
role of noncoding Xist RNA in X-chromosome inactivation
coats the X chromosome that will be inactivated and recruits histone modifying enzymes to the X chromosome that will be inactivated
in situ hybridization can be used to localize a gene of interest due to the ability of a cloned DNA sequence to hybridize to a chromosome through __________ base pairing
complementary
the additional compaction involved in converting an interphase chromosome into a metaphase chromosome is brought about by protein complexes called
condensins
regions surrouding the centromeres that remain condensed during most of the cell cycle are described as...
constitutive heterochromatin
H2A, H2B, H3, and H4 are the...
core histones
during FISH, chromosomal DNA is made single-stranded by a process called __________. the single-stranded DNA is then hybridized to a single-stranded DNA ______ tagged with a fluorescent label
denaturation; probe
idiograms
diagrams of the reproducible banding patterns obtained by chemical staining of chromosomes
what affect does acetylation have on lysines in core histone protein tails?
eliminates the positive charge on lysine, disrupting the electrostatic attraction between the histone and the negatively charged DNA backbone
initiation of X-chromosome inactivation occurs in the human ____....
embryo, about two weeks after fertilization
a synthetic yeast chromosome is...
entirely human-made in a DNA synthesizer machine
nonhistone proteins are responsible for...
enzymatic activity in DNA replication assisting w. chromosome segregation regulating transcription and RNA processing forming the structural backbone of the chromosome
regions of chromosomes that have less condensed chromatin are called
euchromatin
DNA replication proceeding bidirectionally from multiple origins of replication is characteristic of...
eukaryotic chromosomes
features that distinguish eukaryotic chromosomes from bacterial chromosomes: - eukaryotic chromosomes are linear - eukaryotic chromosomes contain less DNA - eukaryotic chromosomes contain more DNA - eukaryotic chromosomes are circular - in eukaryotic chromosomes, DNA is wound into nucleosomes
eukaryotic chromosomes are linear in eukaryotic chromosomes, DNA is wound into nucleosomes eukaryotic chromosomes contain more DNA
chromatin that can interconvery between heterochromatin and euchromatin
facultative heterochromatin
the best description of an inactivated X chromosome in a somatic cell of a human female is...
facultative heterochromatin
T/F: all genes on the inactivated X chromosome remain inactivated throughout life in a somatic cell of an adult female
false
F/T: methlation of histone tails always leads to the formation of heterochromatin and repression of transcription
false (it depends on the a.a. being methylated)
a method used to identify the locations of specific DNA sequences on chromosomes displayed in a karyotype is called
fluorescent in situ hybridization (FISH)
the use of a chemical dye to obtain an reproducible pattern of dark and light bands on chromosomes is called
giemsa staining or G-banding
in Drosophila, HP1 is a protein that promotes the formation of
heterochromatin
heterochromatin
highly condensed chromosomal regions within which genes are usually transcriptionally inactive.
for histone methylation, ________ _______ add methyl groups and ________ ______ remove methyl groups
histone methyltransferases; histone demethylases
what is the transcriptional activity of heterochromatin
inactive
euchromatin is ______ condensed than heterochromatin and contains transcriptionally-_________ genes
less; active
nucleosomes can change in...
location and covalent modifications to the amino-terminal tails of histones
'q' portion of the chromosome is the...
long arm of the chromosome
level of chromatic compaction of chromosome in metaphase of mitosis cause what type of condensation
loops of chromatin containing 60-100kb of DNA are drawn together in a radial pattern by nonhistones scaffold proteins
modification of histone N-terminal tails occurs by the addition of _________ groups to specific lysines and arginines and/or _______ group to specific lysines
methyl; acetyl
as a general rule, the less frequently a DNA segment is transcribed, the __________ it is compacted
more
telomeres consist of....
multiple repeats of a specific DNA sequence
Xist (X inactive specific transcript)
ncRNA transcribed from the XIC of the X chromosome that becomes a Barr body; Xist ncRNA binds to the X chromosome and mediates X chromosome inactivation.
in a nucleosome, the DNA can associate with the histone proteins because the DNA has a _________ charge and the histone proteins have a __________ charge
negative; positive
properties of the noncoding RNA molecule called Xist...
never leaves the nucleus and is never translated into a protein
place these observed and hypothesized levels of chromosome compaction in order from least to most compact (starting at the top): radial loop-scaffold supercoiling to produce a 300 angstroms fiber nucleosome fiber of 100 angstroms
nucleosome fiber of 100 angstroms supercoiling to produce a 300 angstroms fiber radial loop-scaffold
fxn. of ARS in the YAC vector
origin of replication
a situation where heterochromatin can prevent the expression of a nearby gene in some cells but not others is called
position-effect variegation
fxn. of telomeres in the YAC vector
prevents chromosome degradation
histone acetylation
prevents close packing of nucleosomes and therefore favors gene expression
the enzyme telomerase is composed of...
protein & RNA
of the two main types of molecule found within eukaryotic chromosomes, ______ are largely responsible for chromosome compaction
proteins
FISH analysis can be used to detect changes in chromosome _________, such as deletion, duplication or translocations
rearrangement
facultative heterochromatin
regions of chromosomes (or even whole chromosomes) that are heterochromatic in some cells and euchromatic in other cells of the same organisms.
nonhistone proteins assist with a number of processes such as DNA replication and chromsome segregation, but majority of nonhistone proteins serve to...
regulate transcription and RNA processing during gene expression
DNA extending from one origin of replication to the endpoints where it merges with the DNA from adjoining replication forks is called a...
replicon
somatic cells have a limited life span because
they do not typically express the telomerase enzyme and it causes their chromosomes to shorten with time
the function of largest class of nonhistone proteins in chromatin is to enhance or regulate...
transcription and RNA processing
DNA sequences found within constitutive heterochromatin include _________ elements and long stretches of simple __________ sequences
transposable; repetitive
T/F: eukaryotic chromosomes tend to shorten over time because RNA primers are removed from the 5' ends but not replaced by DNA nucleotides
true
the RNA component of the telomerase enzyme is....
used as a template to add new repeats to the ends of telomeres and complementary to the repeated sequences in telomeres
position-effect variegation (PEV)
variable expression of a gene in a population of cells, caused by the gene's location near highly compacted heterochromatin.
the 5'-TTAGGG repeating sequence of the telomere is found in a....
wide variety of eukaryotic species