Chapter 12 Cell division plays an important role in an organism s ability to reproduce replace dead cells and in overall growth of a multicellular organism Cell division is referred to as the Cell Cycle I Consists of a cycle of molecular reactions leading to an increase in cell number 1 2 types a cell cycle and mitosis b cell cycle and meosis Both focus on nuclear division II Cell Division DNA Replication Before a cell divides it has to make a copy of its DNA o The process is called DNA Replication DNA Synthesis In prokaryotic cells a cell will grow elongate to 2x its normal size and then divide into 2 cells This process is called Binary Fission A Defined as prokaryotic cell division B Produces two identical daughter cells a Genetically identical o DNA replication occurs during prokaryotic cell elongation o Binary fission results in the production of 2 daughter cells that are identical to the parent cell In eukaryotic cells there is more DNA o In a resting cell DNA is loosely coiled Chromatin in the nucleus o In a dividing cell the DNA tightly packs into a Chromosome Our cells have 23 pairs of chromosomes 46 in all All 23 pairs have to be replicated into sister chromatids o Consist of an original chromosome attached at its centromere to its copy The copy is attached to the original chromosome at the centromere III Cell Division 2 Types 1 Mitosis Cell Cycle In animals the daughter cells are identical to the parent cell 1 Involves somatic cells Purposes 1 Tissue regeneration or cell replacement 2 Growth and development Initially its divided into two major phases A Interphase a Three subphases G1 Phase S phase and G2 Phase i ii iii G1 Phase cell prepares to enter S Phase S Phase DNA replication of all 23 pairs of chromosomes S stands for synthesis resulting in 23 pairs of sister chromatids major part of cell divison G2 Phase cell prepares to enter mitosis of the mitotic phase B Mitotic phase a Mitosis focuses on nuclear division i Prophase and Prometaphase DNA tightly coils into sister chromatids The mitotic spindle made up of microtubules begins to form coming off the centrioles which are non membranous organelles located in a region called centriosome The centrioles migrate to opposite ends of the cell Prometaphase The nuclear envelope disassembles Sister chromatids at their centromeres attach to their mitotic spindle both sides At the centriomeres they have a protein complex called the kinetochore ii Metaphase iii Anaphase The sister chromatids are aligned end to end forming the metaphase plate Separation of the sister chromatids into daughter Pulled apart towards opposite ends Motor proteins of the kinetochore walk along the mitotic chromosomes spindle How chromosomes move through anaphase iv Telophase Overlaps with cytokinesis Mitotic spindle disassembles Nuclear envelopes membranes reassemble and they contain DNA Daughter chromosomes becomes loosely coiled chromatin b Cytokinesis i ii iii Defined as division of the cytoplasm by the cell membrane pinching inward resulting in two cells Overlaps with telophase of mitophase Ring of proteins called microfilaments that helps pull the phospholipids inward 2 iv To form two completely different daughter cells Somatic cells divide by mitosis A All are somatic cells 2 Meiosis Cell Cycle B Genetic information in somatic cells is NOT passed on to offspring In animals the daughter cells are not identical to the parent cell Involves Gametes And may not be identical to each other Gametes sex cells produced by meiosis o Genetic information is passed on to offspring Both types of cell division involve a cycle of events chemical reactions therefore cell division The cell cycle in eukaryotic cells is tightly regulated to ensure 2 normal functioning cells are is also called the Cell Cycle produced For somatic cells the cell cycle including mitosis consists of the phases listed below C Interphase a G1 phase G Gap b S phase S Synthesis DNA Replication c G2 phase Healthy non dividing cells are in G0 phase B Mitotic M phase a Mitosis Division of the nucleus and DNA i Prophase ii Prometaphase iii Metaphase iv Anaphase v Telophase b Cytokinesis division of the cytoplasm Proteins control the timing of the cell cycle Cyclins Cyclin dependent kinases 3 If the cell is not ready it will not continue past cell cycle checkpoints The parent cell entering this cell cycle is a somatic diploid cell 2n The n is the number of chromosomes and the 2 represents the number of sets of chromosomes 2 x 23 or 23 pairs The two daughter cells produced during this cell cycle are also identical to the parent cell IV Mitosis This cell cycle including mitosis results in the production of more diploid cells 2n Involves somatic cells which contain genetic information not passed on to offspring Somatic cells include all cell types except gametes One cell 2N will divide into two identical daughter cells 2N Mitosis is part of the cell cycle s Mitotic M phase a Mitosis Consists of 5 phases involving nuclear division i Prophase Prometaphase o The sister chromatids condense o The mitotic spindle is assembled attached to centrioles Located at the centrosomes at opposite ends of the cells o The nuclear envelope disassembles o The mitotic spindle attaches to the Kinetochore located at the sister chromatid s centromere ii Metaphase iii Anaphase o Begins when the nuclear envelope disappears o Attached to the mitotic spindle the sister chromatids are aligned end to end forming the metaphase plate o Begins when the kinetochore at the centromeres of the sister chromatids separate the sister chromatids into daughter chromosomes Kinetochores are protein structures that include motor proteins 4 Motor proteins walk the chromosome along kinetochore microtubules Microtubules shorten as chromosome walks past o The daughter chromosomes are pulled to opposite ends of the cell iv Telophase o The mitotic spindle is disassembled o The nuclear envelope is reassembled o The daughter chromosomes uncoil Chromatin b Cytokinesis o Begins during telophase and is completed by the end of telophase o The division of the cell cytoplasm o In animal cells the cell membrane is pinched inward by a contractile ring of microfilaments resulting in two daughter cells 2n o In plants a new cell wall forms IV Cancer Oncogenesis Begins with genetic mutations leading to uncontrolled cell growth that may lead to the formation of a tumor mass of cells or an increase in cell number white blood cells Mostly caused by an accumulation