Ch 7 Book Terms

Question 1

nucleoid

Answer 1

The structure in a prokaryotic cell that contains the genome. The DNA is bound to proteins and is not enclosed by a membrane.

Question 2

chromatin

Answer 2

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.

Question 3

packing ratio

Answer 3

The ratio of the length of DNA to the unit length of the fiber containing it.

Question 4

capsid

Answer 4

The external protein coat of a virus particle.

Question 5

nucleation center

Answer 5

A duplex hairpin in TMV (tobacco mosaic virus) in which assembly of coat protein with RNA is initiated.

Question 6

terminase

Answer 6

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.

Question 7

domain

Answer 7

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.

Question 8

macrodomains

Answer 8

Large contiguous regions on chromosomes that appear to act as independent units. Four such regions have been identified in
Escherichia coli.

Question 9

ori

Answer 9

A sequence of DNA at which replication is initiated.

Question 10

ter

Answer 10

The DNA sequence that signals for the termination of replication.

Question 11

matrix attachment regions (MARs)

Answer 11

A region of DNA that attaches to the nuclear matrix. It is also known as a scaffold attachment site (SAR).

Question 12

scaffold reattachment regions (SARs)

Answer 12

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.

Question 13

euchromatin

Answer 13

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.

Question 14

heterochromatin

Answer 14

Regions of the genome that are highly condensed, are not transcribed, and are late replicating. It is divided into two types: constitutive and facultative.

Question 15

chromocenter

Answer 15

An aggregate in the nucleus of heterochromatin from different chromosomes.

Question 16

constitutive heterochromatin

Answer 16

The inert state of particular (often repetitive) DNA sequences, such as satellite DNA.

Question 17

facultative heterochromatin

Answer 17

The inert state of sequences that also exist in active copies (e.g., one mammalian X chromosome in females).

Question 18

chromosome territories

Answer 18

The discrete three-dimensional spaces occupied by individual chromosomes in the interphase nucleus.

Question 19

G-bands

Answer 19

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).

Question 20

bands

Answer 20

Portions of polytene chromosomes visible as dense regions that contain the majority of DNA; they include active genes.

Question 21

interbands

Answer 21

The relatively dispersed regions of polytene chromosomes that lie between the bands.

Question 22

chromomeres

Answer 22

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.

Question 23

cytological map

Answer 23

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.

Question 24

microtubule organizing centers (MTOCs)

Answer 24

The structure in eukaryotic cells from which the microtubules emerge. It organizes flagella/cilia and the mitotic and meiotic spindle apparatus.

Question 25

centromere

Answer 25

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.

Question 26

cohesins

Answer 26

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.

Question 27

spindle

Answer 27

A structure made up of microtubules that guides the movements of the chromosomes during mitosis.

Question 28

holocentric

Answer 28

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.

Question 29

kinetochore

Answer 29

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.

Question 30

telomere

Answer 30

The natural end of a chromosome; the DNA sequence consists of a simple repeating unit with a protruding single-stranded end.

Question 31

t-loop

Answer 31

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.

Question 32

shelterin

Answer 32

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.

Question 33

telomerase

Answer 33

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.