1. Chapter 12

2.  Described by Rudolf Virchow in 1855.  involves the distribution of genetic material (chromosomes) from parent to daughter cell  Functions ◦ reproduction of an entire organism (single- celled)—asexual reproduction ◦ Allows multicellular organisms to develop from a single cell ◦ renewal and repair (replacing dead cells and healing wounds)

3.  life of a cell from time it was split from parent cell until it divides into two daughter cells  Different in cell types ◦ Prokaryotes  Binary fission ◦ Eukarytotes--somatic cells (body cells)  mitosis (identical cells) ◦ Eukaryotes--gametes (sperm and egg)  meiosis (non-identical cells)

4.  DNA exists as chromatin in cells not undergoing division (mitosis)  During mitosis chromatin condenses into chromosomes  Duplicated chromosome = sister chromatid ◦ attached at centromere

5.  Interphase ◦ 90% of the cell cycle ◦ divided into:  G 1 “growth/gap 1” (grow)  S “synthesis” (chromosomes copied)  G 2 “growth/gap 2” (grow and prepare for division)

6.  Mitotic (M) Phase (mitosis)--division of genetic material ◦ prophase- chromosomes condense (sister chromatids), mitotic spindle forms, centrosomes (centrioles) migrate to opposite ends ◦ prometaphase- nuclear membrane disappears, microtubules (spindle fibers) begin to attach to chromatids (centromere/kinetochore) ◦ metaphase- chromosomes line up on metaphase plate (middle of cell), all microtubules attached to chromatids ◦ anaphase- chromatid pairs are pulled apart and move toward opposite ends of cell ◦ telophase- two nuclei begin to form, chromosomes unwind, cytoplasm begins to pinch inward (cleavage)  Cytokinesis--complete division of cytoplasm

7.  Frequency of cell division varies with cell type, which is crucial to normal growth, development and maintenance  Cell cycle regulated at certain checkpoints by internal and external signals. ◦ a “stop and go” signal which regulates the cycle  Allows the cell to determine if there is enough nutrients and raw materials to move to the next phase of the cycle ◦ located in G 1, G 2, and M phases

8.  In Eukaryotes, cellular reproduction must be controlled to maintain the form and function of different parts of the body ◦ Prokaryotes reproduce constantly when environmental conditions are optimal  Progression through the phases of the cell cycle is tightly regulated  Some cells never reproduce and enter G 0 phase, a “non-dividing” phase ◦ Cells may be here for a designated period of time or forever…  Nerve and muscle cells

9.  G 1 checkpoint triggered by DNA damage  S checkpoint triggered by incomplete DNA replication  G 2 checkpoint triggered by DNA damage  M checkpoint triggered by chromosome not attaching to spindle

10.  Regulatory Molecules ◦ protein kinases  enzymes that activate or inactivate other proteins by phosphorylation; help in cell signaling  “go” signals in G 1 and G 2 ◦ cyclins  Proteins that activate the kinases by attaching (cyclin-dependent kinases- -Cdks)  Allosteric regulation  levels rise and fall in response to concentration of kinase

11.  MPF (maturation/mitosis promoting factor): triggers passage into M-phase. Concentration declines as mitosis proceeds, eventually stopping mitosis ◦ PDGF (platelet derived growth factor): produced in blood (platelets), helps stimulate connective tissue to heal after injury

12.  Regulatory mechanisms are missing in cells (due to mutations)  Cells divide excessively and become invasive; “faulty cell cycle control” ◦ benign vs. malignant tumors ◦ chemotherapy alters cell cycle (prevents it from occurring), but targets cancerous as well as normal cells  can stop dividing at random points in cell cycle, or can be “immortal” and divide indefinitely ◦ HeLa Cells