Genetics Eukaryotic Chromosome
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
Referring to the figure, match the name of the YAC vector component on the left with its function on the right
ARS <--> Origin of replication Centromere <--> Allows for proper chromosome segregation Telomere <--> Prevents chromosome degradation TRP+ <--> Selectable marker Foreign DNA <--> Cloned DNA to be transferred
Which features distinguish eukaryotic chromosomes from bacterial chromosomes
Eukaryotic chromosomes are linear. Eukaryotic chromosomes contain more DNA. In eukaryotic chromosomes, DNA is wound into nucleosomes.
Which is the best description of an inactivated X chromosome in a somatic cell of a human female
Facultative heterochromatin
In the diagram, the black arrows point at ________ proteins, and the yellow arrow points at a strand of __________
Histone, DNA
The enzyme telomerase has two components which are
RNA and protein
The template used for adding new repeating units to telomeres is found in the
RNA component of telomerase
Without telomeres, eukaryotic chromosomes would shorten over time as cells divide because
RNA primers at the 5' ends of new strands cannot be replaced by DNA nucleotides
Which roles does the noncoding Xist RNA play in X-chromosome inactivation
Recruits histone modifying enzymes to the X chromosome that will be inactivated Coats the X chromosome that will be inactivated
What is euchromatin
Regions of chromosomes that are less condensed
A kinetochore is a chromosomal structure where
a spindle fiber will attach during chromosomal division
N-terminal tails of histones can be chemically modified by the addition of ______ and/or ______ groups
acetyl; methyl
When nucleosomes assemble on newly-replicated DNA, the histones within each nucleosome
are a random mixture of "old" recycled histones and newly-synthesized histones
DNA segments that prevent the spread of heterochromatin into regions of euchromatin are called
barrier elements
If a segment of chromatin is subjected to histone deacetylation, it will likely
become more condensed, which will repress gene expression
On a eukaryotic chromosome, DNA replication proceeds
bidirectionally, from multiple origins of replication
The protein that forms a complex to hold sister chromatids together is called
cohesin
An enzyme that removes acetyl groups from histone proteins is called a histone
deacetylase
Telomere sequences
do not encode proteins consist of short repeated sequences
Chromosome centromeres are
essential for precise distribution of chromosomes during cell division the sites where sister chromatids are most tightly bound together the sites where kinetochores form, to allow spindle fiber attachment
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
One of the two X chromosomes in the somatic cells of human females is inactivated. Either the chromosome from the woman's mother or the one from her father can be inactivated. The inactivated X chromosome is best described as _________ heterochromatin.
facultative
The 5'-TTAGGG repeating sequence of the telomere is
found in a wide variety of eukaryotic species
Of the five histone proteins, four are assembled into the nucleosome core but the fifth histone, called _______ is located outside the core.
h1
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
Cohesin is a protein complex that
holds sister chromatids together
Positively charged _________ on the N-terminal tails of core histone proteins can be acetylated by the enzyme _________ _________
lysines Histone acetyltransferase
Modification of histone N-terminal tails occurs by the addition of ______ groups to specific lysines and arginines and/or ______ groups to specific lysines
methyl; acetyl
An enzyme that adds methyl groups to a histone N-terminal tail is called a histone ________ while an enzyme that removes methyl groups is a histone _______
methyltransferase demethylase
For histone methylation, histone ______ add methyl groups and histone ______ remove methyl groups
methyltransferases; demethylases
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
A replicon includes DNA duplicated from ______ origin(s) of replication
one
Before DNA replication, all eukaryotic chromosomes contain ______
one linear, double-stranded DNA molecule
Fruit fly eye color is usually red due to the expression of the wild type w+ allele. An inversion can bring the w+ allele into the vicinity of a heterochromatic region so that w+ expression is silenced in some cells. This situation, where eyes with red and white patches develop, is called
position-effect variegation
Histone acetylation
prevents close packing of nucleosomes and therefore favors gene expression.
If a eukaryotic chromosome lacked telomeres, it would tend to shorten over time because RNA _______ are removed from the 5' ends but not replaced by DNA nucleotides
primers
The enzyme telomerase is composed of
protein RNA
Almost all of the transcriptional activity of chromosomes is observed in
regions of euchromatin
Telomerase is an enzyme that
restores sequences at the ends of chromosomes
A short DNA sequence of 5-300 base pairs that is repeated from thousands to millions of times in tandem is called ______ DNA
satellite
Satellite DNAs are
short DNA sequences repeated thousands to millions of times in a tandem array
Centromeres are sites where ______ are most tightly bound together
sister chromatids
What is a Barr body
An inactivated X chromosome in mammalian somatic cells
The inactivated X chromosome in somatic cells of mammals, like the red-staining structure labeled Xi in the image, is called a
Barr body
In the diagram of the nucleosome, to what do the black and red arrows point?
Black arrows: core histones; Red arrow: DNA
What is the name of the complex of DNA and protein found within eukaryotic chromosomes
Chromatin
Chromatin is the complex of ________ and ___________ found within eukaryotic chromosomes
DNA protein
Barrier elements are
DNA segments that block the spread of heterochromatin
Working with protein extracts from African frog eggs, scientists have been able to disassemble and reassemble metaphase chromosome. Which of the following proteins were sufficient for chromosome assembly in vitro
DNA topoisomerase II Condensins Histones Histone chaperones
Are DNA compaction and gene expression related and if so, how
In general, the more a segment of DNA is transcribed, the less it is compacted
What is the histone composition of a nucleosome that has just been assembled on a newly replicated DNA molecule
It contains a random mixture of newly formed and recycled histones
What is the histone composition of a nucleosome that has just been assembled on a newly replicated DNA molecule?
It contains a random mixture of newly formed and recycled histones
Choose the three main constituents of chromatin (each makes up about a third of chromatin)
Nonhistone proteins Histones DNA
In addition to DNA and proteins, chromatin seems to contain a significant amount of chromatin-associated _________ , whose roles are not well understood
RNA
What is facultative heterochromatin
Regions of chromosomes that heterochromatic in some cells and euchromatic in other cells
Which features are found in a Yeast Artificial Chromosome (YAC)
Telomere Large fragment of foreign DNA Centromere Origin of replication Selectable marker
In a nucleosome, what is the nature of the chemical attraction between the histone proteins and the DNA
The basic histone proteins are attracted to the phosphate groups along the DNA backbone
Scientists have been able to generate a yeast strain that has a single giant chromosome. Choose all features of this cell
The giant chromosome has a single centromere. The giant chromosome has two telomeres.
What is heterochromatin
The tightly compacted regions of chromosomes
Select all proteins that form the core of a nucleosome
Two H2A Two H3 Two H4 Two H2B
What is the composition of the nucleosome core?
Two H2A, two H2B, two H3, two H4
In order to facilitate chromosome inactivation, Xist RNA coats the ________ chromosome and recruits ________ modifying enzymes.
X Histone
In somatic cells of human females one of the two X chromosomes is randomly turned off. What is this mechanism called
X-chromosome inactivation
What is the primary role of the 450 kb region of DNA in the human X chromosome known as the XIC
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
The Xist gene produces ______, leading to inactivation
a noncoding RNA that coats the X chromosome
A change from a DNase resistant site to a DNase hypersensitive site is observed for promoters of genes that are becoming
activated
Enzymes called histone acetyltransferases
add acetyl groups to specific lysine residues in a histone
During in vitro experiments, scientists were able to isolate proteins from the large eggs of the African frog and reassemble metaphase chromosomes. They only needed four proteins to mimic most steps of this process: histones, histone _______, __________, and DNA topoisomerase II
chaperones condensins
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
DNA in chromosomes forms long loops by passing twice through ring-shaped protein complexes known as
condensins
Protein, ring-shaped complexes that form loops during the compaction of DNA in chromosomes, are called _____
condensins
Regions of chromosomes that are heterochromatic in some cells and euchromatic in other cells of the same organism are called ________ heterochromatin
facultative
In humans with a typical constitution of chromosomes, X-chromosome inactivation induces dosage compensation by randomly inactivating one of the X chromosomes in the somatic cells of
females
A method used to identify the locations of specific DNA sequences on chromosomes displayed in a karyotype is called
fluorescent in situ hybridization (FISH)
In chromatin, it is possible to detect when a gene is activated because its promoter region becomes a DNase ________ site
hypersensitive
What is the transcriptional activity of heterochromatin?
inactive
A synthetic yeast chromosome
is entirely human-made in a DNA synthesizer machine
During chromosomal division in eukaryotes, spindle fibers attach to
kinetochores
Unlike bacterial chromosomes, eukaryotic chromosomes are ______, have ______ DNA, and have the DNA organized into ______
linear; more; nucleosomes
Fluorescent in situ hybridization (FISH) is a method used to
locate specific DNA sequences on chromosomes displayed in a karyotype
In a nucleosome, the DNA can associate with the histone proteins because the DNA has a _______ charge and the histone proteins have a __________ charge
negatively positively
The noncoding RNA molecule called Xist
never leaves the nucleus is never translated into a protein
A long RNA molecule that is never translated is called a long ______ RNA
noncoding
Histone H1 is found _______
outside the nucleosome core
Match the name on the left to the appropriate portion of the chromosome on the right
p <---> Short arm of the chromosome q <--> Long arm of the chromosome Centromere <--> Chromosome location where kinetochore forms Telomere <--> Structure at the end of a linear chromosome
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
A situation where heterochromatin can prevent the expression of a nearby gene in some cells but not others is called ________ ________ variegation
position effect
A histone deacetylase is an enzyme that ______ acetyl groups from/on histone N-terminal tails
removes
DNA extending from one origin of replication to the endpoints where it merges with the DNA from adjoining replication forks is called a
replicon
The enzyme that restores sequences which extend the ends of chromosomes is called
telomerase
Each end of a eukaryotic chromosome has a protective structure called a(n)
telomere
The structures found at both ends of a eukaryotic chromosome are called
telomeres
Histone proteins can be chemically modified by adding acetyl or methyl groups to ______ which extend outward from the nucleosome
their N-terminal tails
The predominant satellite found in human centromeres is called
α-satellite
