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Lecture 3

week 3 - chp19.docx

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Health Sciences
HSCI 100
Nienke Van Houten

CHAPTER 19: CELL DIVISION CHROMOSOMES – tightly coiled combination of a DNA molecule that contains genetic info for the organism and specialized proteins called histones - Gene: specific segment of the DNA that directs synthesis of a protein - 1 of 23 = sex chromosomes, 22 others = autosomes (Expression of most ppl inherited characteristics) - Diploid (2n) – 2 copies of each chromosome - Haploid (n) – one copy of each chromosome THE CELL CYCLE 3 basic stages: - Growth - Division o Mitosis – what somatic/germ cells do o Meiosis – only what germ cells do - Homeostasis & repair 1. Interphase - Longest time. Cell carries out function & grows - Before division, time of intense preparation - DNA & organelles duplicated - - G1 stage –growth o Cell grows in size & accumulates materials o Proteins needed for DNA replication are synthesized o Each chromosome has DNA molecule &proteins - S stage – DNA Synthesis (replication) o DNA replication occurs, copy of each chromosome (Sister chromatids) o Chromosome copies remain attached - G2 stage – growth o Proteins needed for division are synthesized (microtubules/centrioles) 2. Cell division (mitosis & cytokinesis) - Mitosis – nuclear division (separation of chromatids) – 2 identical daughter cells o Functions:  Responsible for cell replacement, growth & development  Highly regulated  If regulation fails then defective/uncontrolled mitosis = tumors o One nucleus divides into 2 daughter nuclei containing same # and kinds of chromosomes o 1. PROPHASE – chromosomes condense  Centrosomes duplicated, chromatin condense into chromosomes and nuclear envelope fragments  Nucleolus disappears – duplicated chromosomes visible  Centrosomes begin moving apart & spindle begins forming  In cytoplasm – mitotic spindle forms o 2. METAPHASE – chromosomes line up @ equatorial plate  Ensures that each cell receives chromatid from each 46 chromosomes o 3. ANAPHSE – attachments between sister chromatids break o 4. TELOPHASE – new nuclei form, each 2 with complete sets of chromosomes  Nuclear envelopes & nucleoli reappear - Cytokinesis – cytoplasmic division divides into 2 daughter cells o Begins toward end of mitosis (sometimes during telophase) o Band of microfilaments in the area where the chromosomes align form a furrow where furrow deepens and pinch the cell in two Karyotypes - arrangement of chromosomes based on their physical characteristics (e.g. length/position of centromere) MEIOSIS (ovaries&testes) – 4 non identical daughter cells (half # of chromosomes as parent) Meiosis I – separate homologues - Prophase I – premeiotic interphase o Dna replicates, copies remain attached by centromere o Each copy = chromatid - Metaphase I, Anaphase I, Interkinesis (no replication of DNA)/telophase I/cytokinesis - Chromosome number reduce
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