Ch 7 Book Terms Flashcards
nucleoid
The structure in a prokaryotic cell that contains the genome. The DNA is bound to proteins and is not enclosed by a membrane.
chromatin
The combination of DNA and proteins that make up the contents of the nucleus of a cell. Its primary functions are to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene expression and DNA replication and repair. The primary protein components are histones that compact the DNA.
packing ratio
The ratio of the length of DNA to the unit length of the fiber containing it.
capsid
The external protein coat of a virus particle.
nucleation center
A duplex hairpin in TMV (tobacco mosaic virus) in which assembly of coat protein with RNA is initiated.
terminase
An enzyme that cleaves multimers of a viral genome and then uses hydrolysis of ATP to provide the energy to translocate the DNA into an empty viral capsid starting with the cleaved end.
domain
In reference to a chromosome, it may refer either to a discrete structural entity defined as a region within which supercoiling is independent of other regions or to an extensive region including an expressed gene that has heightened sensitivity to degradation by the enzyme DNase I. In a protein, it is a discrete continuous part of the amino acid sequence that can be equated with a particular function.
macrodomains
Large contiguous regions on chromosomes that appear to act as independent units. Four such regions have been identified in
Escherichia coli.
ori
A sequence of DNA at which replication is initiated.
ter
The DNA sequence that signals for the termination of replication.
matrix attachment regions (MARs)
A region of DNA that attaches to the nuclear matrix. It is also known as a scaffold attachment site (SAR).
scaffold reattachment regions (SARs)
DNA sites attached to proteinaceous structures in both metaphase and interphase nuclei. Chromatin appears to be attached to an underlying structure in vivo; evidence suggests that this attachment is necessary for transcription or replication.
euchromatin
Regions that comprise most of the genome in the interphase nucleus, are less tightly coiled than heterochromatin, and contain most of the active or potentially active single-copy genes.
heterochromatin
Regions of the genome that are highly condensed, are not transcribed, and are late replicating. It is divided into two types: constitutive and facultative.
chromocenter
An aggregate in the nucleus of heterochromatin from different chromosomes.
constitutive heterochromatin
The inert state of particular (often repetitive) DNA sequences, such as satellite DNA.
facultative heterochromatin
The inert state of sequences that also exist in active copies (e.g., one mammalian X chromosome in females).
chromosome territories
The discrete three-dimensional spaces occupied by individual chromosomes in the interphase nucleus.
G-bands
Bands generated on eukaryotic chromosomes by staining techniques that appear as a series of lateral striations. They are used for karyotyping (i.e., identifying chromosomes and chromosomal regions by the banding pattern).
bands
Portions of polytene chromosomes visible as dense regions that contain the majority of DNA; they include active genes.
interbands
The relatively dispersed regions of polytene chromosomes that lie between the bands.
chromomeres
Densely staining granules visible in chromosomes under certain conditions, especially early in meiosis, when a chromosome may appear to consist of a series of such granules.
cytological map
A schematic representation of chromosomes that indicates the arrangement of individual genes. Created by analyzing the banding patterns of chromosomes that have undergone changes such as deletions and mutations.
microtubule organizing centers (MTOCs)
The structure in eukaryotic cells from which the microtubules emerge. It organizes flagella/cilia and the mitotic and meiotic spindle apparatus.
centromere
A constricted region of a chromosome that includes the site of attachment (the kinetochore) to the mitotic or meiotic spindle. It consists of unique DNA sequences and proteins not found anywhere else in the chromosome.
cohesins
Proteins that regulate the separation of sister chromatids during cell division. They hold the sister chromatids together after DNA replication until anaphase, at which point their removal leads to the separation of the sister chromatids.
spindle
A structure made up of microtubules that guides the movements of the chromosomes during mitosis.
holocentric
Type of chromosome in some species whereby the centromeres are diffuse and spread out along the entire length of the chromosome. Species with these chromosomes still make spindle fiber attachments for mitotic chromosome separation, but do not require one and only one regional or point centromere per chromosome.
kinetochore
A small organelle associated with the surface of the centromere that attaches a chromosome to the microtubules of the mitotic spindle. Each mitotic chromosome contains two “sisters” that are positioned on opposite sides of its centromere and face in opposite directions.
telomere
The natural end of a chromosome; the DNA sequence consists of a simple repeating unit with a protruding single-stranded end.
t-loop
Structure characterized by a series of TTAGGG repeats that are displaced to form a single-stranded region, and the tail of the telomere is paired with the homologous strand.
shelterin
A complex of six telomeric proteins in mammals that function to protect telomeres from DNA damage repair pathways and to regulate telomere length control by telomerase.
telomerase
The ribonucleoprotein enzyme that creates repeating units of one strand at the telomere by adding individual bases to the
DNA 3′ end, as directed by an RNA sequence in the RNA component of the enzyme.
