Chapter 5 - Principals of biology

Somatic cell

Body cell; excludes cells that undergo meiosis and become sperm or eggs.

Apoptosis

Programmed cell death; involves a cascade of specific cellular events leading to death and destruction of the cell.

Cell cycle

An ordered sequence of events in eukaryotes that involves cell growth and nuclear division; consists of the stages G1, S, G2, and M.

Interphase

Stages of the cell cycle (G1, S, G2) during which growth and DNA synthesis occur when the nucleus is not actively dividing.

Chromatid

Following replication, a chromosome consists of a pair of sister chromatids, held together at the centromere; each chromatid is comprised of a single DNA helix.

Sister chromatid

One of two genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere.

Mitosis

The stage of cellular reproduction in which nuclear division occurs; process in which a parent nucleus produces two daughter nuclei, each having the same number and kinds of chromosomes as the parent nucleus.

Cytokenis

Division of the cytoplasm following mitosis or meiosis.

Growth factors

A hormone or chemical, secreted by one cell, that may stimulate or inhibit growth of another cell or cells.

proto-oncogene

Gene that promotes the cell cycle and prevents apoptosis; may become an oncogene through mutation.

tumor supressor genes

Gene that codes for a protein that ordinarily suppresses the cell cycle; inactivity due to a mutation can lead to a tumor.

oncogene

Cancer-causing gene formed by a mutation in a proto-oncogene; codes for proteins that stimulate the cell cycle and inhibit apoptosis.

chromatin

Network of DNA strands and associated proteins observed within a nucleus of a cell.

diploid (2n)

Cell condition in which two of each type of chromosome are present.

haploid

Cell condition in which only one of each type of chromosome is present.

centromere

Constriction where sister chromatids of a chromosome are held together.

spindle

Collection of microtubules that assist in the orderly distribution of chromosomes during cell division.

prophase

First phase of mitosis; characterized by the condensation of the chromatin; chromosomes are visible, but scattered in the nucleus.

prometaphase

Phase of cell division that occurs between prophase and metaphase and is characterized by attachment of the spindle fibers to the kinetochores of each sister chromatid.

metaphase

Third phase of mitosis; chromosomes are aligned at the metaphase plate

anaphase

Fourth phase of mitosis; chromosomes move toward the poles of the spindle.

telophase

Final phase of mitosis; daughter cells are located at each pole.

clevage furrow

Indentation in the plasma membrane of animal cells during cell division; formation marks the start of cytokinesis.

cell plate

Structure across a dividing plant cell that signals the location of new plasma membranes and cell walls.

meiosis

Type of nuclear division that reduces the chromosome number from 2n to n; daughter cells receive the haploid number of chromosomes in varied combinations; also called reduction division.

homologous chromosome

Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologue.

synapsis

Pairing of homologous chromosomes during meiosis I.

gametes

Haploid sex cell (e.g., egg or sperm).

fertilization

Fusion of sperm and egg nuclei, producing a zygote that develops into a new individual.

crossing over

Exchange of segments between nonsister chromatids of a bivalent during meiosis.

independant assortment

Alleles of unlinked genes segregate independently of each other during meiosis so that the gametes can contain all possible combinations of alleles.

interkinesis

Period of time between meiosis I and meiosis II during which no DNA replication takes place.

zygote

Diploid cell formed by the union of two gametes; the product of fertilization.

spermatogenesis

Production of sperm in males by the process of meiosis and maturation.

oogenesis

Production of eggs in females by the process of meiosis and maturation.

sperm

Male gamete having a haploid number of chromosomes and the ability to fertilize an egg, the female gamete.

polar body

Nonfunctional product of oogenesis produced by the unequal division of cytoplasm in females during meiosis. In humans, three of the four cells produced by meiosis are polar bodies.

egg

Also called an ovum; haploid cell that is usually fertilized by a sperm to form a diploid zygote