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Unformatted text preview: Dr. Brown LSB 416 x 2-8563 Deborah.brown @sunysb.edu Office hours: Thurs. and Fri 2-3 PM Today's lecture: Reproduction of cells; MITOSIS Chap 12 pp. 218-225 All cells in any organism are genetically identical (have the same DNA) When ANY cell reproduces (divides): Each "daughter cell" gets the same amount of DNA First step in division of ANY cell: Duplication of chromosome(s) A chromosome: contains ONE molecule of DNA Prokaryotes (organism is one cell): have 1 chromosome (1 DNA molecule) NO MITOSIS IN PROKARYOTES!!! Bacterial Cell Division Chromosome replicates and attaches to the membrane Bacterial Cell Division Attachment sites separate as cell grows Bacterial Cell Division Cell divides; each new cell has one chromosome! Eukaryotic cells: cell cycle Cells divide ONLY at a specified time. 4 Phases of Cell Cycle: G1 interphase S G2 M = mitotic phase } S phase = DNA synthesis Mitotic phase: When cells divide Interphase: When cells are NOT dividing Mitotic phase: 1) Mitosis: separation of duplicated chromosomes 2) Cytokinesis; cell division Eukaryotes: several chromosomes in each cell; in the nucleus Chromosomes; only visible by microscopy during mitosis Chromosomes in mitosis DNA in a nucleus in interphase In interphase: diffuse chromatin fills the nucleus Chromatin: DNA + protein DNA in each human cell: 2-3 m long 2 nm wide Folded to fit in cell. Many proteins are attached. Chromatin: partially folded DNA + attached proteins. Too unfolded to see individual chromosomes. ("ball of string") Chromosomes fold very tightly in mitosis. Allows separation without tangling. Prelude to mitosis: 1. In S phase (in interphase); chromosomes replicate. Identical copies stay attached to each other. Duplicated chromosome has 2 sister chromatids attached at the centromere. Duplicated chromosome has 2 sister chromatids attached at the centromere. One sister chromatid (contains 1 molecule of DNA) Duplicated chromosome has 2 sister chromatids attached at the centromere. Centromere 2. Late in interphase; centrosome and centrioles replicate. Asters (short microtubule arrays extending from centrosomes) form 5 phases of mitosis 1. Prophase. A. Chromatin condenses into visible "chromosomes". B. Mitotic spindle (microtubules) forms in cytoplasm between centriole pairs; lengthens as microtubules grow. 2. Prometaphase: A. nuclear envelope fragments B. mitotic spindle invades nucleus C. microtubules bind chromatids at kinetochores Kinetochore: region of centromere where microtubules attach 3. Metaphase A. Centrosomes at opposite ends of cell B. Chromosomes (attached to MT's) line up at metaphase plate (center of cell) Kinetochore MT's: Attach to chromatids Non-kinetochore MT's: Go from centrosome toward metaphase plate; overlap At metaphase: Equal + opposite forces try to pull sister chromatids to opposite spindle poles 4. Anaphase Sister chromatids separate and are pulled toward opposite poles. kinetochore MT's shorten. Kinetochore MT's shorten as tubulin subunits are removed from the kinetochore end; next to chromatids Motor proteins "walk" along MT's to pull chromatids In anaphase, centrosomes move farther apart as nonkintochore MT's get longer and slide past each other ** Spindle gets longer* 5. Telophase A. Nuclear envelopes reform (now 2 separate nuclei) B. Chromosomes partly unfold Cytokinesis (starts during telophase) Different in animal And plant cells Animal cells: Microfilaments under plasma membrane pinch in; form cleavage furrow to squeeze cell in half Cytokinesis; plant cells. Vesicles line up in cell center to form cell plate. Fusion creates new plasma membrane. ...
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- Fall '08