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1362-SU09-Lecture-1-_36706

1362-SU09-Lecture-1-_36706 - Omniscellula...

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“Omnis cellula e cellula” (“every cell from a cell” – Virchow, 1855) The ability to reproduce is a fundamental property of all life; this process is cell based and is referred to as cell division . Depending on the organism, cell division can have different roles: 100 μm 200 μm 20 μm (a) Reproduction; asexual (b) Growth & development from fertilized egg (c) Tissue renewal (Regeneration) Unicellular types: Prokaryotes & k Multicellular Eukaryotes These types of cell division yield daughter cells Eukaryotes genetically equivalent to the parent cell; i.e., clones.
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Organization of Genetic Material • Cell division involves the accurate replication and equal parti tioning of a cell’s DNA (genome) into two daughter cells. • This is a relatively simple & rapid process for prokaryotes that possess a single, circular double helical DNA molecule, compared to… • … eukaryotes , whose DNA is packaged into multiple, linear chromosomes inside a nucleus. [a human cell’s genome >6 feet long!] Chromosomes in a cell of a lily • Eukaryotic species possess a particular chromosome number in each cell nucleus. Somatic cells: 2 chromosome sets; diploid (2n) . Gametes : 1 chromosome set; haploid (n) . Pl id d ib t f h d Ploidy : describe sets of chromosomes possessed by a eukaryote; e.g., tetraploid (4n) • Eukaryotic chromosomes: Eukaryotic chromosomes: Each is composed of DNA wound around specific proteins; this DNA:protein assemblage is called chromatin .
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Eukaryotic DNA • The massive amount of DNA (10 9 bp) in a eukaryote assumes a Chromatin structure of a highly coiled configuration in order to fit in the nucleus. chromosome is shown: In non dividing cells, or in cells replicating their DNA, chromosomes appear as thin chromatin filaments. degree of coiling increases Chromosomes assume a more highly condensed (compacted) form f ll i DNA li ti i ti f ll di i i following DNA replication, in preparation for cell division. Condensation of chromosomes facilitates their movement during cell division. DNA is compacted by coiling it around spherical proteins called histones; this assemblage (i.e., DNA & protein) is referred to as chromatin :
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Eukaryotic Chromosome Terminology Sister chromatids 0.5 μm Chromosomes DNA molecules are identical*; held together by d i Chromosome duplication (including DNA Chromo some arm condensin proteins; most closely attached at synthesis) Centromere Sister the centromere . The process of mitosis results in chromatids Separation of i t h tid separation & segregation of sister chromatids Centromere sister chromatids & their movement to two new nuclei Sister chromatids forming in the cell. * one exception: meiosis
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Mitosis = Nuclear Division Mitosis Nuclear membrane disappears then reforms Genetically identical cells Nuclear membrane disappears…then reforms (diploid) Diploid cell Chromosomes replicate: sister h id Chromosomes align & 2 l i f Cytokinesis: division of chromatids segregate;2 nuclei form Cell is briefly tetraploid.
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