cell cycle
sequence of stages through which a cell passes between cell divisions
interphase
extended period of growth and development between cell divisions; includes checkpoints, G1 phase, S Phase, G2 phase
M phase
mitotic phase; period of active cell division
G1 phase
gap 1; the cell grows and necessary proteins are synthesized; lasts several hours
G1/S checkpoint
near the end of G1; holds the cell in G1 until all of the enzymes necessary for DNA replication are synthesized; once this checkpoint is passed, the cell is committed to cell division
S phase
DNA synthesis where each chromosome is replicated; at the end of S phase, each chromosomes has two chromatids; this phase can last 9 hours
G0
non-dividing phase; the cell can remain in G0 for an extended period of time or it can reenter G1
G2 phase
gap 2; biochemical events occur that are necessary for cell division; this phase lasts about 4 hours
G2/M checkpoint
near the end of G2; cell cannot proceed if DNA is damaged; the cell cannot enter the M phase unless this checkpoint is cleared
M phase
sister chromatids separate; contains six stages: prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis
prophase
chromosomes become condensed and are visible under a light microscope; each chromosome has two sister chromatids; the mitotic spindle forms
centriole
organelle composed of mictotubules that duplicate and migrate to opposite poles of the cell; the centriole is the center of the centrosome
centrosome
in animal cells, microtubules grow out of the centrosome and attach to the centromere of each chromosome
prometaphase
the nucleus disintegrates and the mitotic spindle microtubules attach to the kinetochore of each chromatid
metaphase
chromosomes become arranged along a plane called the metaphase plate located between the two centrosomes
anaphase
sister chromatids are separated and move toward opposite poles of the cell
telophase
separated chromosomes arrive at the spindle poles; the nuclear membrane reforms; the chromosomes relax
cytokinesis
the cytoplasm is divided between the two newly formed cells
prokaryote
small unicellular organisms with no nucleus, membrane bound organelles or cytoskeleton, containing circular DNA
eukaryote
uni- or multicellular organisms with a membrane-bound nucleus and organelles, cytoskeleton, linear DNA complexed with histones
eubacteria
prokaryotic bacterial type (true bacteria)
archaea
prokaryotic bacterial type (ancient bacteria) more closely related to eukaryotes than to eubacteria
nucleus
genetic material is surrounded by a nuclear envelope to define this eukaryotic cellular organelle; also a fundamental difference between prokaryotes and eukaryotes
histone
protein used to package DNA into chromosomes; histones limit access to DNA; contained in eukaryotes and in some archaea
chromatin
complex of DNA and histone proteins
plasmids
extra circular piece of DNA found in some bacteria that may contain important genes (for the organism)
viruses
composed of an outer protein coat that surrounds either DNA or RNA; they depend on their host cells for existence; not an evolutionary distinct group but closely related to their host(s)
3 fundamental events for cellular reproduction
1) copy genetic information
2) separate copies from one another
3) division of the cell
origin of replication
sequence of DNA where replication is initiated
nuclear matrix
internal scaffolding of the nucleus composed of protein fibers that maintain precise spatial relations during all nuclear events
homologous pair
two sets of chromosomes due to sexual reproduction; one set inherited from each parent; alike in structure, size, and genetic information for the same set of hereditary characteristics; the chromosomes hae the same pattern of genes but the nature of the g
allele
one of the alternative forms of a gene; in diploid cells there are two alleles of any one gene occupying the same relative position on homologous chromosomes
diploid
cells carrying two sets of genetic information (somatic cells in humans)
haploid
cells containing one set of genetic information (one copy of each gene as in reproductive cells (eggs, sperm, spores))
fundamental chromosome structure
1) centromere
2) pair of telomeres
3) origins of replication
centromere
chromosomal attachment point for spindle microtubules; metacentric (centromere at the center); submetacentric (centromere just off center); acrocentric (centromere toward one end) telocentric (centromere at the end)
kinetochore
protein and RNA complex that assembles on the centromere for spindle microtubule attachment
chromosomal arms in submetacentric and acrocentric chromosomes
p = short arm; q = longer arm
telomeres
end of a chromosome consisting of tandemly repeated short sequences of DNA ensuring that each cycle of replication is completed
telomere theory of aging
some sequences in the telomere are lost each time a cell divides; after 60-100 divisions, the cell dies
sister chromatids
each chromosome divides lengthwise to produce two identical copies of a chromosome held together at the centromere