chapter 5 Flashcards
proteins _: they _
perform most of the cell’s functions:
serve as building blocks for cell structures; they form the enzymes that catalyze the cell’s chemical reactions; they regulate the activity of genes; and they enable cells to move and to communicate with one another.
chro- mosomes contain both _ and _
DNA
protein
DNA, after all, is simply a _ composed of _, which are _.
long polymer
only four types of nucleotide subunits
chemically very similar to one another
DNA=
deoxyribonucleic acid (DNA)
the two strands are held together by _ bonds
hydrogen
With the exception of the _ (_) and highly special- ized cells that _ (such as _), human cells each contain two copies of every chromosome, one inherited from the mother and one from the father.
gametes
sperm and eggs
lack DNA entirely
mature red blood cells
Each chromosome can be “_” a different color using _
painted
_
sets of chromosome-specific DNA molecules coupled to different fluorescent dyes.
An earlier and more traditional way of distinguishing one chromosome from another involves _.
staining the chromosomes with dyes that bind to certain types of DNA sequences
_
These dyes mainly distin- guish between DNA that is rich in A-T nucleotide pairs and DNA that is G-C rich, and they produce a predictable pattern of bands along each type of chromosome. The resulting patterns allow each chromosome to be identified and numbered.
An ordered display of the full set of _ human chromosomes is called the human _
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karyotype
_ analyze karyotypes to detect chromosomal abnormalities that are associated with some _ (Figure 5–9) and with certain types of _
Cytogeneticists
inherited disorders
cancer
A gene is often defined as a _
segment of DNA that contains the instructions for making a particular protein or RNA mol- ecule.
Together, the total genetic information carried by a complete set of the chromosomes present in a cell or organism constitutes its _.
genome
the total number of genes is about _ for the simplest bacterium and about _ for humans.
500
24,000
However, chromosomes from many eukaryotes—includ- ing humans—contain, in addition to genes and the specific nucleotide sequences required for normal gene expression, a large _
excess of interspersed DNA
DNA must be able to be replicated, and the replicated copies must be separated and partitioned equally and reliably into the two daughter cells at each cell division. These processes occur through an ordered series of events, known collectively as the _.
cell cycle
_, when chro- mosomes are duplicated, and _, the much more brief stage when the duplicated chromosomes are distributed, or segregated, to the two daughter nuclei.
interphase
mitosis
One type of nucleotide sequence, called a _, is where DNA replication begins; eukaryotic chromosomes contain _ to _
replication origin
many replication origins
allow the long DNA molecules to be replicated rapidly
Another DNA sequence forms the _ that mark the ends of each chromosome. Telomeres contain _ that are required for the ends of chromosomes to be _.
telomeres
repeated nucleotide sequences
fully replicated
telomeres also serve as a _ that keeps the chromosome tips from _.
protective cap
_
being mistaken by the cell as broken DNA in need of repair.
Eukaryotic chromosomes also contain a third type of specialized DNA sequence, called the _, that allows duplicated chromosomes to be separated during M phase (see Figure 5–14). During this stage of the cell cycle, the DNA coils up, adopting a more and more compact structure, ultimately forming highly compacted, or condensed, mitotic chromosomes
centromere
The proteins that bind to DNA to form eukaryotic chromosomes are traditionally divided into two general classes: the _ and the _ chromosomal proteins.
The complex of both classes of protein with nuclear DNA is called _.
histones
nonhistone
chromatin
Histones are responsible for the first and most fundamental level of chromatin packing: the formation of the _.
nucleosome
The interphase nucleus is the _
nucleus of a cell when it is not dividing
Eukaryotic cells have several ways to adjust rapidly the local structure of their chromatin. One way takes advantage of a set _. These protein machines use the energy of ATP hydrolysis to change the position of the DNA wrapped around _
of ATP-dependent chromatin-remodeling complexes
_
nucleosomes
Interphase chromatin is not uniformly packed. Instead, regions of the chromosome containing genes that are being actively expressed are generally more _, whereas those that contain silent genes are more _.
extended
condensed
The most highly condensed form of interphase chromatin is called _
heterochromatin
Heterochromatin typically makes up about 10% of an interphase chromosome, and in mammalian chromosomes, it is concentrated around the _ region and in the _ DNA at the chromosome ends
centromere
telomeric
we use the term euchromatin to refer to _
chromatin that exists in a less condensed state than heterochromatin
In female mammals, one X chromosome is _ to prevent _ of X-linked genes.
This inactivation occurs randomly in early embryonic development by _
inactivated
overexpression
the X chromatin being highly condensed forming heterochromatin –> inactivation
Life depends on the _, _, and _ of genetic information.
stable storage
maintenance
inheritance
Genetic information is carried by _ and is encoded in _.
very long DNA molecules
_
the linear sequence of four nucleotides: A, T, G, and C
Each molecule of DNA is a _ composed of _, _, which are held together by _ between _.
double helix
a pair of antiparallel
complementary DNA strands
hydrogen bonds
G-C and A-T base pairs
The genetic material of a eukaryotic cell—its _—is contained in _, each formed from _.
genome
_
a set of chromosomes
_
a single, enormously long DNA molecule that contains many genes
When a gene is expressed, part of _ is _, most of which are _.
its nucleotide sequence
transcribed into RNA molecules
translated to produce a protein
The DNA that forms each eukaryotic chromosome contains, in addition to _, many _, one _, and _. These special DNA sequences ensure that, before cell division, each chromosome can be _, and that the resulting daughter chromosomes can be parceled out _.
genes
replication origins
centromere
two telomeres
duplicated efficiently
equally to the two daughter cells
In eukaryotic chromosomes, the DNA is tightly folded by _. This complex of DNA and protein is called _.
binding to a set of histone and nonhistone chromosomal proteins
_
chromatin
Histones _–protein particles called _, which further _.
pack the DNA into a repeating array of DNA
_
nucleosomes
_
fold up into even more compact chromatin structures
A cell can regulate _—temporarily _ or _ particular regions of its chromosomes—using _ and _ in various ways.
its chromatin structure
decondensing
condensing
chromatin-remodeling complexes
enzymes that covalently modify histone tails
The loosening of chromatin to a more decondensed state allows proteins involved in _, _, and _ to gain _
gene expression
DNA replication
DNA repair
access to the necessary DNA sequences.
Some forms of chromatin have a pattern of _ that causes the DNA to become so highly condensed that its genes _; a high degree of condensation occurs on all chromosomes during _ and in the _.
histone tail modification
cannot be expressed to produce RNA
mitosis
heterochromatin of interphase chromosomes
The 5’ end of the sugar has a _ attached to the _.
phosphate group
5th carbon
The 3’ end of the sugar has a _ (-OH) attached to the _. This is the site where _ during the _.
hydroxyl group
3rd carbon
new nucleotides are added
elongation of the DNA/RNA strand
DNA is made of four _
nucleotide building blocks.
Each nucleotide is composed of _
a sugar phosphate covalently linked to a base
The nucleotides are _ linked together into _, with a _ from which the —, _, _, and _ (A, C, G, and T)—extend.
covalently
polynucleotide chains
sugar-phosphate backbone
bases
adenine
cytosine
guanine
thymine
A DNA molecule is composed of _ polynucleotide chains (DNA strands) held together by _
two
_
hydrogen bonds between
the paired bases.
polarity at the _ end
3’
_ hydrogen bonds form between A and T, whereas _ form between
G and C
two
three
The bases can pair in this way only if the two polynucleotide chains that contain them are _
antiparallel
DNA has at chemical _; that is, _
polarity
its two ends are chemically different
Most genes contain information to make _.
proteins
Note that for a minority of genes, the final product is the _. In these cases, _ is complete once the nucleotide sequence of the DNA has been transcribed into the _.
RNA molecule itself
gene expression
nucleotide sequence of its RNA
Chromosome painting is done by exposing the _ tagged with _.
The labeled DNA probes can only bind to their matching sequences on the chromosome (hybridization).
chromosomes to single-stranded DNA molecules
_
fluorescent dyes
each “gene” is
considered to include both _
the “coding strand” and its complement.
_ DNA sequence elements are needed to produce a eukaryotic chromosome that can be duplicated and then segregated at mitosis. Each
chromosome has _, one _, and two _.
Three
multiple origins of replication
centromere
telomeres
The DNA replicates in _, beginning at the _ and proceeding _along the chromosome.
interphase
origins of replication
bidirectionally from each origin
In M phase, the _ attaches the _ to the _ so that one _.
centromere
_
compact, duplicated chromosomes
_
mitotic spindle
_
copy will be distributed to each daughter cell when the cell divides
Prior to cell division, the centromere also helps to hold the _.
duplicated chromosomes together until they are ready to be pulled apart
Telomeres contain _ that allow for the _.
DNA sequences
complete replication of chromosome ends
The nucleolus is the most prominent structure in the _
interphase nucleus.
The _ is the most prominent structure in the interphase nucleus.
nucleolus
Heterochromatin contains _ genes and
is located _ of the nucleus, immediately under the _.
few
mainly around the periphery
nuclear envelope
The large, dark region within the nucleus is the _, which contains the _
nucleolus
genes for ribosomal RNAs.
Nucleosomes contain _.
DNA wrapped around a protein core of eight histone molecules
When the DNA around each isolated nucleosome core particle is released, its length is found to be _ nucleotide pairs
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“beads-on-a-string” form of _
chromatin
The chromatin in human chromosomes is folded into looped domains. These loops are established by _ that bind to specific DNA sequences, creating a clamp at the base of each loop.
special nonhistone chromosomal proteins
after DNA packing, EACH DNA MOLECULE HAS BEEN PACKAGED INTO A _ THAT IS _ SHORTER THAN ITS FULLY EXTENDED LENGTH
MITOTIC CHROMOSOME
10,000-FOLD
_ locally reposition the DNA wrapped around nucleosomes.
This large complex contains _ subunits, including one that _ and four that recognize _.
Chromatin-remodeling complexes
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hydrolyzes ATP
specific covalently modified histones
Chromatin-remodeling complexes use _ to loosen the _ and push it along the _.
the enzyme can _ a sequence of DNA, controlling its availability to other _
energy derived from ATP hydrolysis
nucleosomal DNA
histone octamer
expose or hide
DNA-binding proteins.
The pattern of modification
of histone tails can determine _.
how a stretch of chromatin is handled by the cell
most modifications occur on the _, for which _ amino acids are shown.
N-terminal tail
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Acetylation of lysines, for instance, can reduce the _ of the tails for adjacent nucleosomes, thereby _ chromatin structure and _ particular nuclear proteins.
affinity
loosening
allowing access to
Both ATP-dependent chromatin-remodeling complexes and _ are tightly regulated.
histone-modifying enzymes
Histone-modifying enzymes work in concert with the chromatin-remodeling complexes to _, allowing local chromatin structure to change rapidly according to the needs of the cell.
condense and relax stretches of chromatin
_ work in concert with the _ to condense and relax stretches of chromatin, allowing local chromatin structure to change rapidly according to the needs of the cell.
Histone-modifying enzymes
chromatin-remodeling complexes
_ allow heterochromatin to form and to
spread.
Heterochromatin-specific histone modifications
histone modifications attract _ that reproduce the same histone modifications on neighboring _. In this manner, heterochromatin can spread until it encounters a _ that blocks further propagation into regions of euchromatin.
heterochromatin-specific proteins
nucleosomes
barrier DNA sequence
HETEROCHROMATIN-SPECIFIC PROTEINS, INCLUDING _
HISTONE-MODIFYING ENZYMES
X chromosome inactivation is _. Some genes on the inactivated X chromosome _.
not entirely complete
“escape” this process and remain active
The X chromosome contains several genes associated with the _, including _, which plays an important role in detecting and fighting _.
immune system
TLR7 (Toll-Like Receptor 7)
viral infections
Griffith showed that heat-killed infectious bacteria can transform _
into _.
harmless live bacteria
pathogens
Griffith found that a _ in the pathogenic S strain could _, the nonlethal R strain into the deadly S strain.
substance present
permanently change, or transform
