Bio 305- Chapter 12
Ways that nucleosomes can change
-Change in location -Covalent modifications to the amino-terminal tails of histones
Which roles does the noncoding Xist RNA play in X-chromosome inactivation?
-Coats the X chromosome that will be inactivated -Recruits histone modifying enzymes to the X chromosome that will be inactivated
Chromatin is a complex of _____ and _____ found within eukaryotic chromosomes
-DNA -Protein
Events of nucleosome assembly in order from earliest to latest
1) Newly sythesized DNA is formed 2) An H3-H4 teramer binds 3) Two H2A-H2B dimers bind
Steps involved in fluorescence in situ hybridization (FISH) in correct order
1) Obtain cells in the metaphase stage of mitosis 2) Drop cells on a slide and treat them wiht agents that cause them to burst 3) Denature chromosomal DNA 4) Hybridize chromosomal DNA to a single-stranded DNA probes that are tagged with a fluorescence lable 5) View with a fluorescence microscope
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
Which of the following describes the nucleic acid molecule(s) found in a single eukaryotic chromosome (or a chromatid if the chromosome has been replicated)?
A single, long, linear molecule of double-stranded DNA
Chromatin that can interconvert between heterochromatin and euchromatin is called ____ heterochromatin
Facultative
Which is the best description of an inactivated X chromosome in a somatic cell of a human female?
Facultative heterochromatin
T or F: Heterochromatin is transcriptionally active
False
In Drosophila, a protein that binds to methylated histone H3 tails and promotes the formation of heterochromatin is
HP1
Which one represents the highest level of chromosome compaction that has been observed or hypothesized?
Radial loop-scaffold
If a segment of chromatin is subjected to histone deacetylation, it will likely
become more condensed, which will repress gene expression
An enzyme that removes acetyl groups from histone proteins is called histone
deacetylase
Which of the following causes of genetic disorders can be detected with FISH analysis?
deletions, duplications, translocations
The initiation of X-chromosome inactivation occurs in the human
embryo, about two weeks after fertilization
Regions of chromosomes that have less condensed chromatin are called
euchromatin
A region of a chromosome with highly compacted chromatin is called
heterochromatin
Core ____ proteins contain a globular domain and a flexible amino-terminal tail. DNA wraps around the globular domains, and the amino-terminal tails protrude from the chromatin.
histone
Histone acetylation
prevents close packing of nucleosomes and therefore favors gene expression
Electron microscope studies of chromatin have detected a 300 Angstrom fiber that is formed by
supercoiling of nucleosomes
Telomere sequences
-Do not encode proteins -Consist of short repeated sequences
The nucleosome core includes two each of four histones named _____, _____, ______, and ______.
-H2A -H2B -H3 -H4
What are the core histones of the nucleosome?
-H2A -H2B -H3 -H4
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
Nonhistone proteins are responsible for
-Regulating transcription and RNA processing - enzymatic activity in DNA replication - assisting with chromosome segregation -Forming the structural backbone if the chromosome
N-terminal tails of histones can be chemically modified by the addition of _____ and/or _______ groups.
-acetyl -methyl
Which features distinguish the centromeres of higher eukaryotes from yeast centromere sequences?
-bind to many microtubules -larger -contain many more repeating units
The RNA component of the telomerase enzyme is
-complementary to the repeated sequences in telomeres - used as a template to add new repeats to the ends of telomeres
For histone methylation, histone _____ add methyl groups and histone _____ remove methyl groups.
-methyltransferases -demethylases
The noncoding RNA molecule called Xist
-never leaves the nucleus -is never translated into a protein
To distinguish between the portions of the chromosome on either side of the centromere, geneticists use the letter ______ to denote the shorter arm and the letter ______ to indicate the longer arm
-p -q
The inactivated X chromosome is somatic cells or mammals, like the red-staining structure labeled Xi in the image, is called ______ ______.
Barr body
DNA elements that prevent the spread of heterochromatin into regions of euchromatin are called
Barrier elements
Protein complexes that help in the compaction of interphase chromosomes into metaphase chromosomes are called
Condensins
Cohesin is a protein complex that
Holds sister chromatids together
As a general rule, the less frequently a DNA segment is transcribed, the _______ it is compacted
More
Which molecule found within eukaryotic chromosomes is responsible for the compaction of chromosomes?
Protein
DNA extending from one origin of replication to the endpoints where it merges the DNA from adjoining replication forks is called a
Replicon
A short DNA sequence of 5-300 base pairs that is repeated from thousands to millions of times in tandem is called ___ DNA
Satellite
Form the octamer of core histone proteins in a nucleosome
Two of each -H2A -H2B -H3 -H4
In somatic cells of human females one of the two X chromosomes is randomly turned off. What is this mechanism called?
X-chromosome inactivation
The 450 kb region on the X chromosome that plays an important role in X chromosome inactivation is the _______
XIC
The gene that produces a noncoding RNA that is essential for X-chromosome inactivation is called
Xist
DNA sequences found within constitutive heterochromatin include _____ elements and long stretches of simple _____ sequences
_transposable -repetitive
The Xist gene produces _______, leading to inactivation
a noncoding RNA that coats the X chromosome
In chromatin, it is possible to detect when a gene is activated because its promoter region becomes DNase
hypersensitive
Diagrams of the chromosomal banding patterns produced by G-banding are called
idiograms
During in situ hybridization, a DNa probe made from a cloned gene binds to ______.
its complementary sequence on a particular chromosome
Chromosomal division in eukaryotes, spindle fibers attach to
kinetochores
Fluorescent in situ hybridization (FISH) is a method used to
locate specific DNA sequences on chromosomes displayed in a karyotype
A situation where heterochromatin can prevent the expression of a nearby gene in some cells but not others is called ______ -_______ variegation
position-effect
Nonhistone proteins assist with a number of processes such as DNA replication and chromosome segregation, but the majority of nonhistone proteins serve to
regulate transcription and RNA processing during gene expression
Histone deacetylase is an enzyme that _______ acetyl groups from/on histone N-terminal tails
removes
An enzyme that restores sequences to extend the ends of chromosomes is called
telomerase
Each end of a eukaryotic chromosome has a protective structure called a(n)
telomere