"Where a cell exists, there must have been a preexisting cell, just as the animal arises only from an animal and a plant only from a plant." - Rudolf Virchow (1855).
Cell Division functions in reproduction, growth, and repair.
For unicellular organisms cell division results in the production of an entire organism.
In multicellular organism, cell division allows:
A complex process, a dividing cell:
Genome - total endowment of DNA unique to each cell.
Prokaryotes reproduce by binary fission.
DNA attachment site on the plasma membrane.
Chromosomes are threadlike structures in eukaryotic nuclei that are composed of DNA and protein (chromatin). Each species has a characteristic chromosome number; gametes contain half the number of chromosomes as do somatic cells. Each chromosome contains a long DNA molecule with thousands of genes, as well as, various proteins that maintain structure and control gene activity.
Mitosis - (Mitos = thread) Nuclear Division during which duplicated chromosomes are evenly distributed to daughter nuclei. Daughter cells are genetically equivalent to the parent cell. Usually followed by cytokinesis.
Coenocytic - multiple nuclei - e.g., muscle
Cytokinesis - cytoplasmic division that forms two separate daughter cells each containing a single nucleus.
Mitosis alternates with interphase in the cell cycle.
Cell cycle - well ordered sequence of events between the time a cell divides to form two daughter cells and the time those daughter cells divide.
Interphase - period of intense biochemical activity and consists of three periods G1, the first growth phase S, synthesis phase when DNA is replicated and G2, second growth phase.
Mitosis is reliable with only about 1 error in every 100,000 cell divisions.
Prophase
In the nucleus - nucleoli disappear. Chromatin fibers condense into discrete observable chromosomes, composed of two identical sister chromatids joined at the centromere.
In the cytoplasm - Mitotic spindle forms. It is composed of microtubules between the two centrosomes. centrosomes move apart propelled by the lengthening of the microtubules bundles between them.
Late Prophase (or Prometaphase)- nuclear envelope fragments and microtubules interact with the condensed chromosomes. Spindle fibers extend from each pole towards the cell's equator. Each chromatid now has a specialized structure, the kinetochore, located at the region of the centromere. Kinetochore microtubules become attached to the kinetochores and put the chromosomes into an agitated state.
Nonkinetichore (or polar) microtubules radiate from each centrosome and overlap each other without attaching to chromosomes.
Metaphase - centrosomes are at opposite poles. Chromosomes move to the metaphase plate. Centromere of all chromosomes are aligned on the metaphase plate. Kinetochores of sister chromatids face opposite poles. Identical chromatids are attached to kinetochore fibers radiating from opposite ends of the parent cell. Kinetochore and nonkinetochore microtubules together form the spindle.
Anaphase - Paired centromeres of each chromosome move apart. Sister chromatids split into separate chromosomes and move toward opposite poles. Centromere first in a "V" shape. Kinetochore fibers shorten as chromosomes move closer to the pole. The cells move farther apart.
Telophase - Nonkinetochore fibers further elongate the cell. Daughter nuclei begin to form. Nuclear envelopes form around the chromosomes. Nucleoli reappear. Chromatin fiber of each chromosome uncoils and the chromosomes become less visible
Cytokinesis - cytoplasmic division - First, a cleavage furrow forms a shallow grove - a contractile ring of actin microfilaments. This ring contracts until it pinches the parent cell in two.