Warm-up 12/2: Why do cells replicate their DNA? When do cells replicate their DNA? What is the primary purpose of DNA?

Chromosomes pp Cell Cycle and Mitosis pp

Chromosomes: coiled and compact DNA in nucleus DNA wrapped tightly around proteins called histones chromatids: two halves of a dividing chromosome Chromatids joined by a centromere

Chromosome number: each organism has a specific number of chromosomes Sex chromosomes: determine sex of the organism (X or Y) female: XX male: XY Autosomes: all other chromosomes All organisms have two copies that are homologous

Cell Cycle and Mitosis

Cell Cycle 3 major phases Interphase: time between cell divisions - G phases: growth - S phase: copying of DNA M phase (mitosis): division of the nucleus Cytokinesis: division of the cytoplasm

Mitosis (M phase) 2n  4n  2 (2n) Continuous process starts with interphase Need to separate the doubled chromosomes Four phases prophase  metaphase  anaphase  telophase PMAT

Prophase Can see chromosomes Chromatids stay connected by centromeres Nucleolus and nuclear membrane break down Centrosomes and centrioles appear Early mitotic spindle forms

Metaphase Two types of fibers (mitotic spindle) kinetechore fibers: attach to centromere of chromosome polar fibers: extend centrosome to centrosome, push cell apart Fibers line up the chromosomes in middle

Anaphase Chromatids of each chromosomes are pulled apart by fibers Move towards opposite poles of dividing cells

Telophase Chromosomes in opposite ends Spindle fibers break down Nuclear envelope reforms Nucleolus in each cell Cytokinesis

MOVIE

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