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GLOSSARY
Anaphase: (Gk.ana, up + phasis, form). The third stage
of mitosis, beginning when the centromeres of
duplicated
chromosomes
divide
and
sister
chromatids separate from each other, and ending
when a complete set of daughter chromosomes are
located at each of the two poles of the cell.
Apoptosis: A type of cell death in which the cell uses
specialized cellular machinery to kill itself; a cell
suicide mechanism that enables metazoans to
control cell number and eliminate cells that threaten
the animal's survival.
Asters: Radial microtubule arrays in animal cells which
are located around each pair of centrioles.
Binary Fission: A type of asexual reproduction in which
a prokaryotic cell divides into two identical cells.
Cancer: Any malignant growth or tumor caused by
abnormal and uncontrolled cell division.
Checkpoints: Control mechanisms that ensure the
fidelity of cell division in eukaryotic cells. These
checkpoints verify whether the processes at each
phase of the cell cycle have been accurately
completed before progression into the next phase.
Cell:
A basic unit of living matter separated from its
environment
by
a
plasma
membrane;
the
fundamental structural unit of life.
Cell cycle: The cycle of cell growth, replication of the
genetic material and nuclear and cytoplasmic
division.
Cell
Membrane:
A
thin
differentially-permeable
membrane that surrounds the cell's cytoplasm.
Cell plate: A double membrane across the midline of a
dividing plant cell, between which the new cell wall
forms during cytokinesis.
Cell wall: A protective layer external to the plasma
membrane in plant cells, bacteria, fungi, and some
protists.
Cell-cycle control system: A cyclically operating set
of proteins that triggers and coordinates events in
the eukaryotic cell cycle.
Centriole: (Gk. kentron, centre). A structure in an
animal cell, composed of cylinders of microtubule
triplets arranged in a 9 + 0 pattern. An animal cell
usually has a pair of centrioles, which are involved in
cell division.
Centromere: (Gk. kentron, centre + meros, a part). A
constricted region of the chromosome joining two
sister chromatids. The centromere is composed of
highly repeated DNA sequences approximately 220
units in length.
Centrosome: Material present in the cytoplasm of all
eukaryotic cells and important during cell division;
also called microtubule-organizing centre.
Chromatid: One of the usually paired and parallel
strands of a duplicated chromosome, joined by a
single centromere.
Chromatin: (Gk. chroma, colour) The complex of DNA
and proteins that makes up a eukaryotic
chromosome. When the cell is not dividing,
chromatin exists as a mass of very long, thin fibres
that are not visible with a light microscope.
Chromosome aberration: A deviation in the normal
number of chromosomes or in their morphology.
Chromosomes: The self-replicating genetic structures of
cells containing the cellular DNA that bears in its
nucleotide sequence, the linear array of genes.
Cleavage furrow: The first sign of cleavage in an animal
cell; a shallow groove in the cell surface near the old
metaphase plate.
Cleavage: The process of cytokinesis in animal cells,
characterized by pinching of the plasma membrane;
specifically, the succession of rapid cell divisions
without growth during early embryonic development
that converts the zygote into a ball of cells.
Cytokinesis: The physical division of the cytoplasm of a
eukaryotic cell to form two daughter cells, each
housing a newly formed nuclei.
Cytoplasm: [Gk. kytos, vessel + plasma, anything
molded]
The entire contents of the cell, exclusive of the
nucleus, and bounded by the plasma membrane.
Cytoskeleton: A network of assorted protein filaments
attached to the cell membrane and to various
organelles that makes up the framework for cell
shape and movement.
Daughter Cell: One of two cells resulting from the
division of a single cell through mitosis or meiosis.
Differentiation: The structural adaptation of some body
part or a cell for a particular function.
Diploid: An organism or cell having the normal amount
of DNA per cell; i.e., two sets of chromosomes or
twice the haploid number.
Dormancy: Dormancy is a period in an organism's life
cycle when growth, development, and (in animals)
physical activity is temporarily suspended. This
minimizes metabolic activity and therefore helps an
organism to conserve energy.
DNA: Deoxyribonucleic acid; it constitutes the primary
genetic material of all cellular material and the DNA
viruses, and occurs predominantly in the nucleus.
Endoplasmic Reticulum: The endoplasmic reticulum
(ER) is a eukaryotic organelle that forms an
interconnected network of tubules, vesicles, and
cisternae within cells.
Embryo: A minute rudimentary plant contained within a
seed or an archegonium.
Eukaryotes: Advanced cell type with a nuclear
membrane surrounding genetic material and
numerous membrane-bound organelles dispersed in
a complex cellular structure.
Eukaryotic cell: A cell containing membrane bound
nucleus and other sub cellular organelles.
Genome: The ordering of genes in a haploid set of
chromosomes of a particular organism; the full DNA
sequence of an organism. The human genome
contains approximately three billion chemical base
pairs.
Haploid: Having a single set of chromosomes in the
nucleus of each cell. Mosses, and many protists and
fungi, are haploid, as are some insects, bryophytes,
and the gametes of all organisms.
Interphase: Time period between cellular divisions in
which cellular processes such as protein synthesis
are carried out.
Karyokinesis: Organic process consisting of the division
of the nucleus of a cell during mitosis or meiosis.
Kinetochore fibres: Kinetochore fibres are microtubules
that connect kinetochores to spindle polar fibres.
Kinetochore: The kinetochore is a specialized region on
the centromeres of chromosomes. Chromosomes are
attached to polar fibres at their kinetochores via
kinetochore fibres.
Lamins: The fibrous proteins providing structural
function and transcriptional regulation in the cell
nucleus. Nuclear lamins interact with membraneassociated proteins to form the nuclear lamina on the
interior of the nuclear envelope.
Mammals: Mammals (formally Mammalia) are a class of
vertebrate animals whose females are characterized
by the possession of mammary glands.
Meiosis: The process of cell division in which two
nuclear divisions occur with only one chromosome
replication. Each of the resulting gametes receives a
haploid set of chromosomes. There are four haploid
daughter cells resulting from this process.
Metaphase: Phase of mitosis in which the chromosome
pairs line up at the equator of the cell.
Microtubule: A hollow protein cylinder, about 25
nanometers in diameter, composed of subunits of
the protein tubulin. Microtubules grow in length by
the addition of tubulin subunits at the end and are
shortened by their removal.
Mitochondria: Genetically independent organelles that
produce energy for the cells along their many
internal folds, called cristae.
Mitosis: A type of simple cell division within the body,
whereby cells divide into other cells, each with the
full set of chromosomes. Each of these cells receives
an exact copy of the chromosomes in the original
cell. During development, mitosis occurs again and
again, until finally the adult organism is created.
Nuclear membrane: The double membrane which
surrounds the eukaryotic nucleus. It has many pores
in its surface which regulate the flow of large
compounds into and out of the nucleus.
Nucleoid: Region in prokaryotes where the DNA is
concentrated. Unlike a nucleus, it is not bound by a
membrane.
Nucleotide: The "letters" or basic units of DNA,
containing a phosphate group, a 5-carbon sugar, and
a ring-shaped nitrogenous base.
Nucleus: Membrane-bound organelle which contains the
DNA in the form of chromosomes. It is the site of
DNA replication, and the site of RNA synthesis.
Organelle: A membrane-bound structure in a eukaryotic
cell that partitions the cell into regions which carry
out different cellular functions, e.g., mitochondria,
endoplasmic reticulum, lysosomes.
Phragmoplast: A plant cell specific structure that forms
during late cytokinesis. It serves as a scaffold for cell
plate assembly and subsequent formation of a new
cell wall separating the two daughter cells.
Plasmodesmata: Plasma-membrane-lined channels in
the cell wall that interconnects adjacent plant cells.
They consist of a break in the cell wall that is lined
by cell membrane and contain a strand of membrane
that is derived from rough ER called the
desmotubule.
Prokaryote: Literally "before the nucleus", the term
applies to all bacteria and archaea. Prokaryotic cells
have no internal membranes or cytoskeleton. Their
DNA is circular, not linear.
Proliferation: To increase in number or spread rapidly.
Prophase - phase of mitosis in which the chromatin
duplicates itself and thickens into chromosomes, the
spindle fibres form, and the nuclear membrane
disintegrates.
Quiescent: Inactive, at rest, quiet.
Replication: The process whereby DNA makes a copy of
itself before cell division.
Ribosomes: Small organelles found in all cells; involved
in the production of proteins by translating
messenger RNA.
Senescence: The state or process of ageing, especially
in humans; old age; ceasing to divide by mitosis
because of shortening of telomeres or excessive DNA
damage.
Spindle Fibres: An aggregate of microtubules that move
chromosomes during cell division. During prophase
the spindle fibres form at opposite poles of the cell
while as during metaphase the spindle fibres extend
from the cell poles to align chromosomes at the
metaphase plate and during anaphase they pull the
chromatids toward the spindle poles, and lengthen
and elongate the cell.
Telophase - phase of mitosis in which the chromosome
pairs have separated and reached opposite poles of
the cell as the spindle begins to disintegrate, the
nuclear membrane reappears, and the cytoplasm
begins to divide.
Vesicle: A small anatomically normal sac or bladderlike
structure (especially one containing fluid).
Yeast: Any of various single-celled fungi that reproduce
asexually by budding or division.