Lectures 22 & 23 Cell Cycle

Lectures 22 & 23 Cell Cycle - Overview: The Key...

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Unformatted text preview: Overview: The Key Roles of Cell Division The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter The continuity of life is based on the reproduction of cells, or cell division In unicellular organisms, division of one cell reproduces the entire organism Multicellular organisms depend on cell division for Development from a fertilized cell Growth Repair Cell division is an integral part of the cell cycle , the life of a cell from formation to its own division (a) Reproduction (b) Growth and development (c) Tissue renewal 20 m 100 m 200 m Most cell division results in genetically identical daughter cells Most cell division results in daughter cells with identical genetic information, DNA The exception is meiosis, a special type of division that can produce sperm and egg cells Cellular Organization of the Genetic Material All the DNA in a cell constitutes the cells genome A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells) DNA molecules in a cell are packaged into chromosomes 20 m Eukaryotic chromosomes consist of chromatin , a complex of DNA and protein that condenses during cell division Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus Somatic cells (nonreproductive cells) have two sets of chromosomes Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells Distribution of Chromosomes During Eukaryotic Cell Division In preparation for cell division, DNA is replicated and the chromosomes condense Each duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell division The centromere is the narrow waist of the duplicated chromosome, where the two chromatids are most closely attached 0.5 m Centromere Sister chromatids During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei Once separate, the chromatids are called chromosomes Chromosomes Chromosomal DNA molecules Centromere Chromosome arm Chromosome duplication (including DNA replication) and condensation Sister chromatids Separation of sister chromatids into two chromosomes 1 2 3 Eukaryotic cell division consists of Mitosis , the division of the genetic material in the nucleus Cytokinesis , the division of the cytoplasm Gametes are produced by a variation of cell division called meiosis Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell The mitotic phase alternates with interphase in the cell cycle In 1882, the German anatomist Walther Flemming developed dyes to observe chromosomes during mitosis and cytokinesis Phases of the Cell Cycle The cell cycle consists of Mitotic (M) phase...
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Lectures 22 & 23 Cell Cycle - Overview: The Key...

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