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Chapter 8 Cell Cycles.docx

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Matthew Smith

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November 20 2013 Chapter 8: Cell Cycles  Cell growth and division o All cells originate from pre-existing cells through the process of cell division o Important for:  Inc pop size (single celled organisms)  Growing new tissues (e.g: new leaves during plant development)  Asexual reproduction  Replacement of lost cells (lining of gut) and/or damaged cells (wound repair)  Cell cycle in prokaryotic organisms o Replication occupies most of the cell cycle in rapidly dividing prokaryotic cells o Replicated chromosomes are distributed actively to the halves of the prokaryotic cell o Mitosis has evolved from an early form of binary fission  Binary Fission (division in half) o Prokaryotic cells undergo a cycle of binary fission involving coordinated cytoplasmic growth, DNA replication, and cell division, producing two daughter cells from an original parent cell  Cell has to get bigger (needs more components of cell membrane and organelles).  Cell will double in size  DNA is then replicated (will have 2 identical daughter cells)  Cell is then divides into two equal parts, producing two daughter cells from one parent cell  Bacterial Cell Cycle o Replication of bacterial chromosomes consumes most of the time in cell cycle o Begins at single site (“origin of replication, ori”) through rxns catalyzed by enzymes located middle of cell o One the “ori” is duplicated, the two origins actively migrate to the 2 ends of the cell o Division of the cytoplasm then occurs through a partition of cell wall material that grows inward until the cell is separated into two parts  Mitosis and Binary Fission o Believed that the ancestral division process was binary fission, and that mitosis evolved from that process o Variations in mitotic apparatus in modern-day organisms show possible intermediates in evolutionary pathway  The cycle of cell growth and division: overview o Mitotic cell division: DNA replication is followed by equal separation of the replicated DNA molecules and their delivery to daughter cells o Process ensures that the 2 cell products of a division have the same genetic info as the parent cell entering division November 20 2013  Mitosis o Is the basis for:  Growth and maintenance of body mass in multicelled eukaryotes  Reproduction of many single celled eukaryotes o Cell cyles: period of growth followed by nuclear division and cytokinesis  Chromosomes o Of eukaryotes cells are individual, linear DNA molecules w/associated proteins o DNA replication and the duplication of chromosomal proteins convert each chromosome into and structure composed of two exact copies (sister chromatids)  Eukaryotic chromosomes o Chromosomes (composed of proteins and DNA) o Proteins organize DNA  DNA is wrapped around histones which bind to nucleosomes and linker DNA, causing nucleosomes to form coiled structure  Most eukaryotes are diploid o Diploid: has both copies of each chromosomes  In humans every cell has 46 chromosomes (23 pairs) o 2n (2 for diploid)  Cell cycle o Can’t have cell division w/o cell growth o G0: when cell reaches maturity and stops growing (doesn’t happen with all cells, only few) o G1: period of gr
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