1 10 1 Why Cells Divide Cells divide to either reproduce organisms or to grow and repair a multicellular organism cell division generates daughter cells from a parent cell with the transfer of genetic information in the form of DNA from the parent to the daughter cells asexual reproduction generates clones offspring that are genetically identical to the parent sexual reproduction genetic information from two individuals of opposite mating types is combined to produce offspring The majority of eukaryotes reproduce through sexual reproduction which gives rise to genetic diversity binary fission splitting in two Prokaryotes reproduce through binary fission which is a type of asexual reproduction mitotic division process that generates two genetically identical daughter cells from a single parent cell in eukaryotes mitosis the division of the nucleus in a parent cell creates two identical daughter cells cytokinesis splitting of original cytoplasm into two new daughter cells meiosis specialized type of cell division that makes sexual reproduction possible Femaleeggs Male sperm cells diploid set double set of genetic info fertilization merging of egg and sperm to create a single cell zygote single cell created by merging of sperm and egg Inherits one haploid set from egg another from sperm restores diploid set embryo mass of developing cells after zygotes of animals divide mitotically cell differentiation process through which daughter cell becomes different from the parent cell germ line cells small group of gamete producing cells fetus embryo that matures and develops organ systems adult stem cells not committed to specialized functions but can eventually differentiate into specialized cells 10 2 The Cell Cycle cell cycle set sequence of events that make up the life of a typical eukaryotic cell that is capable of dividing Not all of our cells complete the cell cycle many enter the G0 stage and stay there until they are needed Example liver cells interphase longest stage Cell takes in nutrients manufactures proteins and other substances expands in size and conducts special functions May also begin preparations for cell division copying of DNA molecules S phase when replication of DNA that requires the synthesis of new DNA occurs during interphase G1 phase GAP 1 is the first phase in the life of a newborn cell Most cell types start differentiating shortly after entering this phase G2 phase begins after S phase and before the start of cell division G0 phase non dividing state Scientists believe that the G0 state represents a safe haven against cancer because these cells lack cell cycle regulatory proteins so further removed from the capacity to divide and turn into a rogue cell The climax of the cell cycle is cell division 2 tumor clump of rogue cells as a result of rapidly divided cells cancer cells tumor cells turn into these if they begin to invade neighboring tissue prophase first level of mitosis during which DNA molecules undergo a high level of compaction by the end of this DNA is 10x more tightly wound than during interphase Nuclear envelope breaks down late in prophase in a stage called prometaphase This allows mitotic spindle to attach to the now highly condensed chromosomes centrosomes two cytoskeletal structures that begin to move through the cytosol and halt in opposite ends poles of the cell mitotic spindle spoke like array of microtubules functions as a moving crew that hauls chromosomes through the cytoplasm and eventually deposits them at opposite ends of the parent cell metaphase the stage of mitosis when all the replicated chromosomes are arranged in a single plane anaphase the two chromatids in each pair of chromatids break free from one another and are dragged to opposite sides of the parent cell resulting in an orderly partitioning of the replicated genetic information telophase begins when a complete set of daughter chromosomes arrives at spindle pole cell plate forms during telophase appears where the metaphase plate has been Consists of mostly membrane vesicles 11 1 Stem Cells Dedicated to Division Some daughter cells become stem cells while others become highly specialized cell types Stem cells are crucial for human development and maintaining the body in adulthood stem cells undifferentiated cells with the attribute of self renewal can undergo mitotic divisions to make more of itself embryonic stem cells found only in embryos can potentially become any of the 220 cell types in the human body adult stem cells undifferentiated cells that can yield some or all of the specialized cell types of the tissue organ in which they are found can be found in bone marrow where they divide regularly and some become red blood cells platelets or 1 of 8 different types of immune cells others found in skin Loss of stem cells contributes to such signs of aging as graying hair and a weakening of the immune system Depletion of crucial stem cell populations may put an upper limit on the max lifespan of humans about 123 years cell culture lab procedure in which stem cells are spread in a special nutrient broth in a plastic petri dish where they undergo mitotic division to make more stem cells which can be introduced to differentiate into specific cell types regenerative medicine field of medicine that uses stem cells to repair or replace tissues and organs damaged by injury or disease zygote single cell created by the union of egg and sperm embryo subset of cells ball of cells morula created by zygote through the process of several mitotic divisions fetus human embryo AFTER all the organs have formed totipotent cells located in the morula can give rise to any cell type in an organism including the birth sac tissue in mammals 3 blastocyst hollow sphere transformation of the morula that consists of about 150 cells inner cell mass 30 cells located inside the blastocyst gives rise to the embryo proper only source of embryonic stem cells pluripotent cells are capable of producing all of the cell types in the adult body except the tissue that makes up the birth sac in mammals multipotent of or referring to a cell that can differentiate into only a relatively narrow range of cell types unipotent of or referring to a cell type that can differentiate into only one cell type induced pluripotent stem cell iPSC any cell even a highly undifferentiated one that has been genetically reprogrammed to mimic the pluripotent behavior of embryonic stem cells Cells descended from a common parent cell