The Cell CycleBIOLOGY

Key TermsGenomethe total complement of an organisms genesChromatinnetwork of DNA and fibrils in a nucleus that is not dividing.Chromosomestructure of DNA that transmits genetic information to the next generation.Chromatidstwo copies of the same chromosome attached togetherCentromereconstriction where sister chromatids of a chromosome are held together.

Chromatin in a developing salamander ovum

Chromosome NumbersSomatic cells (body cells) diploid (2N) 2 of each chromosome Gametes (sex cells) haploid (N) 1 of each chromosome Examples:Body cellsSex CellsHumans4623Fern 1,262 631Drosophila 8 4Dog7839

MitosisA diploid cell divides to produce diploid daughter cells.Ensures that each daughter cell contains the exact same chromosomes as the original mother cell.Mitosis can occur in either diploid or haploid cells; maintaining either a 2N or N chromosome number.

InterphaseMost of the cell cycle is spent in interphase.G1 - organelles double; accumulates materials for DNA synthesis.S - DNA replication.G2 - Cell synthesizes proteins necessary for cell division.

Prophase & PrometaphaseProphase Chromatin has condensed.Nucleolus disappears.Nuclear envelope disintegrates.Spindle begins to assemble.PrometaphaseKinetochores develop on centromere.Attach sister chromatids to spindle fibers.

Figure 12.5 The stages of mitotic cell division in an animal cell: G2 phase; prophase; prometaphase

Metaphase and AnaphaseMetaphaseChromosomes, attached to kinetochore fibers, are in alignment at center of cell.AnaphaseSister chromatids split, producing daughter chromosomes.Daughter chromosomes are pulled to opposite poles.

TelophaseTelophaseSpindle disappears as new nuclear envelopes form around the daughter chromosomes.Chromosomes become diffuse chromatin again.Nucleolus appears in each daughter nucleus.

CytokinesisAnimal Cells:Cleavage furrow begins asanaphase nears completion.Mitosis without cytokinesis results in a multinucleated cell.

CytokinesisPlant Cells:Rigid cell wall surrounding plant cells does not permit cytokinesis by furrowing.

Figure 12.9 Mitosis in a plant cell

Figure 12-09x Mitosis in an onion root

The Cell Cycle and CancerCancer is a growth disorder that results from the mutation of genes regulating the cell cycle.Lack differentiation.Have abnormal nuclei.Form tumors.Loss of contact inhibition.Undergo metastasis (spread).

ApoptosisOften defined as programmed cell death.

Mitosis increases and apoptosis decreases the number of somatic cells.

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