Chapter 12 Described by Rudolf Virchow in 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) 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) DNA exists as chromatin in cells not undergoing division (mitosis) During mitosis chromatin condenses into chromosomes Duplicated chromosome = sister chromatid attached at centromere 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) 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 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 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 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 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 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 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