Chapter 12 - The Cell Cycle

Question 1

cell division

Answer 1

The reproduction of cells.

Question 2

cell cycle

Answer 2

An ordered sequence of events in the life of a cell, from its origin in the division of a parent cell until its own division into two. The eukaryotic cell cycle is composed of interphase (including G₁, S, and G₂ subphases) and M phase (including mitosis and cytokinesis).

Question 3

genome

Answer 3

The genetic material of an organism or virus; the complete complement of an organism’s or virus’s genes along with its noncoding nucleic acid sequences.

Question 4

chromosome

Answer 4

A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells, Each chromosome consists of one very long DNA molecule and associated proteins. (A bacterial chromosome usually consists of a single circular DNA molecule and associated proteins. It is found in the nucleoid region, which is not membrane bounded.) <em>See also</em> chromatin.

Question 5

chromatin

Answer 5

The complex of DNA and proteins that makes up eukaryotic chromosomes. When the cell is not dividing, chromatin exists in its dispersed form, as a mass of very long, thin fibers that are not visible with a light microscope.

Question 6

somatic cell

Answer 6

Any cell in a multicellular organism except a sperm or egg or their precursors.

Question 7

gamete

Answer 7

A haploid reproductive cell, such as an egg or sperm. Gametes unite during sexual reproduction to produce a diploid zygote.

Question 8

sister chromatids

Answer 8

Two copies of a duplicated chromosome attached to each other by proteins at the centromere and, sometimes, along the arms. While joined, two sister chromatids make up one chromosome. Chromatids are eventually separated during mitosis or meiosis II.

Question 9

centromere

Answer 9

In a duplicated chromosome, the region in each sister chromatid where they are most closely attached to each other by proteins that bind to specific DNA sequences; this close attachment causes a constriction in the condensed chromosome. (An uncondensed, unduplicated chromosome has a single centromere, identified by its DNA sequence.)

Question 10

mitosis

Answer 10

A process of nuclear division in eukaryotic cells conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase, and telophase. Mitosis conserves chromosome number by allocating replicated chromosomes equally to each of the daughter nuclei.

Question 11

cytokinesis

Answer 11

The division of the cytoplasm to form two separate daughter cells immediately after mitosis, meiosis I, or meiosis II.

Question 12

mitotic (M) phase

Answer 12

The phase of the cell cycle that includes mitosis and cytokinesis.

Question 13

interphase

Answer 13

The period in the cell cycle when the cell is not dividing. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase often accounts for about 90% of the cell cycle.

Question 14

G₁ phase

Answer 14

The first gap, or growth phase, of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.

Question 15

S phase

Answer 15

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

Question 16

G₂ phase

Answer 16

The second gap, or growth phase, of the cell cycle, consisting of the portion of interphase after DNA synthesis occurs.

Question 17

prophase

Answer 17

The first stage of mitosis, in which the chromatin condenses into discrete chromosomes visible with a light microscope, the mitotic spindle begins to form, and the nucleolus disappears but the nucleus remains intact.

Question 18

prometaphase

Answer 18

The second stage of mitosis, in which the nuclear envelope fragments and the spindle microtubules attach to the kinetochores of the chromosomes.

Question 19

metaphase

Answer 19

The third stage of mitosis, in which the spindle is complete and the chromosomes, attached to microtubules at their kinetochores, are all aligned at the metaphase plate.

Question 20

anaphase

Answer 20

The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.

Question 21

telophase

Answer 21

The fifth and final stage of mitosis, in which the daughter nuclei are forming and cytokinesis has typically begun.

Question 22

mitotic spindle

Answer 22

An assemblage of microtubules and associated proteins that is involved in the movement of chromosomes during mitosis.

Question 23

centrosome

Answer 23

A structure present in the cytoplasm of animal cells that functions as a microtubule-organizing center and is important during cell division. A centrosome has two centrioles.

Question 24

aster

Answer 24

A radial array of short microtubules that extends from each centrosome toward the plasma membrane in an animal cell undergoing mitosis.

Question 25

kinetochore

Answer 25

A structure of proteins attached to the centromere that links each sister chromatid to the mitotic spindle.

Question 26

metaphase plate

Answer 26

An imaginary structure located at a plane midway between the two poles of a cell in metaphase on which the centromeres of all the duplicated chromoes are located.

Question 27

cleavage

Answer 27

(1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) The succession of rapid cell divisions without significant growth during early embryonic development that converts the zygote into a ball of cells.

Question 28

cleavage furrow

Answer 28

The first sign of cleavage in an animal [or human] cell; a shallow groove around the cell in the cell surface near the old metaphase plate.

Question 29

cell plate

Answer 29

A membrane-bounded, flattened sac located at the midline of a dividing plant cell, inside which the new cell wall forms during cytokinesis.

Question 30

binary fission

Answer 30

A method of asexual reproduction by “division in half.” In prokaryotes, binary fission does not involve mitosis, but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.

Question 31

origin of replication

Answer 31

Site where the replication of a DNA molecule begins, consisting of a specific sequence of nucleotides.

Question 32

cell cycle control system

Answer 32

A cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle.

Question 33

checkpoint

Answer 33

A control point in the cell cycle where stop and go-ahead signals can regulate the cycle.

Question 34

G₀ phase

Answer 34

A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.

Question 35

cyclin

Answer 35

A cellular protein that occurs in a cyclically fluctuating concentration and that plays an important role in regulating the cell cycle.

Question 36

cyclin-dependent kinase (Cdk)

Answer 36

A protein kinase that is active only when attached to a particular cyclin.

Question 37

MPF

Answer 37

Maturation-promoting factor (or M-phase-promoting factor); a protein complex required for a cell to progress from late interphase to mitosis. The active form consists of cyclin and a protein kinase.

Question 38

growth factor

Answer 38

(1) A protein that must be present in the extracellular environment (culture medium or animal [or human] body) for the growth and normal development of certain types of cells.

Question 39

density-dependent inhibition

Answer 39

The phenomenon observed in normal animal [and human] cells that causes them to stop dividing when they come into contact with one another.

Question 40

anchorage dependence

Answer 40

The requirement that a cell must be attached to a substratum in order to initiate cell division.

Question 41

transformation

Answer 41

(1) The conversion of a normal animal [or human] cell to a cancerous cell. (2) A change in genotype and phenotype due to the assimilation of external DNA by a cell. When the external DNA is from a member of a different species, transformation results in horizontal gene transfer.

Question 42

benign tumor

Answer 42

A mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the tumor’s origin.

Question 43

malignant tumor

Answer 43

A cancerous tumor containing cells that have significant genetic and cellular changes and are capable of invading and surviving in new sites. Malignant tumors can impair the functions of one or more organs.

Question 44

metastasis

Answer 44

The spread of cancer cells to locations distant from their original site.