Cell Cycle The repeating set of events in the life of a cell. The repeating set of events in the life of a cell. Includes Includes Interphase Interphase 3 phases 3 phases Cell Division Cell Division Mitosis Mitosis Cytokinesis Cytokinesis

Interphase Period between cell divisions, 3 stages- Period between cell divisions, 3 stages- 1. G 1 phase- Gap 1- Cells grow to mature size. 1. G 1 phase- Gap 1- Cells grow to mature size. 2. S phase- Synthesis- DNA replication. 2. S phase- Synthesis- DNA replication. 3. G 2 phase- Gap 2- Cell prepares for cell division. 3. G 2 phase- Gap 2- Cell prepares for cell division. G O phase- Cell exits the cell cycle (usually after G 1 ) Cells do not copy DNA or prepare to divide. Ex. CNS cells stop dividing at maturity and never divide again. G O phase- Cell exits the cell cycle (usually after G 1 ) Cells do not copy DNA or prepare to divide. Ex. CNS cells stop dividing at maturity and never divide again.

Mitosis Division of the nucleus. Division of the nucleus. Distributes the cells copied DNA to offspring cells. Distributes the cells copied DNA to offspring cells. New cells get the same number and kinds of chromosomes as the parent cell New cells get the same number and kinds of chromosomes as the parent cell 4 phases 4 phases

Prophase (p 156) Chromosomes shorten, thicken and become visible Chromosomes shorten, thicken and become visible Chromatids (replicated chromosomes) lie side by side, attached by a centromere Chromatids (replicated chromosomes) lie side by side, attached by a centromere Centrioles move to opposite ends of the cell (animal cells) Centrioles move to opposite ends of the cell (animal cells) Nuclear membrane breaks down Nuclear membrane breaks down

Metaphase (pp 156, 157) Paired chromosomes line up at the equator of the cell Paired chromosomes line up at the equator of the cell Centromeres attach to the spindle Centromeres attach to the spindle

Anaphase (156, 157) Centromeres split Centromeres split Chromatids separate, becoming individual chromosomes Chromatids separate, becoming individual chromosomes Chromosomes move to opposite poles along spindle Chromosomes move to opposite poles along spindle

Telophase (p 156, 157) Chromosomes uncoil into tangle of chromatin Chromosomes uncoil into tangle of chromatin Nuclear envelope reforms around the chromatin Nuclear envelope reforms around the chromatin

Cytokinesis (p 157) The division of the cytoplasm into two cells The division of the cytoplasm into two cells Animal cells- cell membrane pinches the cytoplasm into two equal parts Animal cells- cell membrane pinches the cytoplasm into two equal parts Plant cells- cell plate forms midway between divided nuclei, plate becomes cell wall Plant cells- cell plate forms midway between divided nuclei, plate becomes cell wall