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Stages of the Cell Cycle • Interphase • Mitosis • Cytokinesis • Cell Differentiation


Interphase •Very active period •Cell grows and performs its routine functions

Interphase includes •G1 phase (G = gap) •S phase (S = synthesis) •G2 phase


G1 Phase • Cell is active & grows • G1 Phase is followed by a restriction “checkpoint” that determines the cell’s fate: • The cell may grow & divide • The cell may remain active, but not divide • The cell may undergo apoptosis = programmed cell death

S Phase •DNA synthesis •Cell replicates DNA

G2 Phase •Cell prepares for division


Figure 3.35 The cell cycle

Interphase: G1 Phase S Phase G2 Phase


Mitosis • Produces 2 daughter cells from 1 cell • Nucleus divides – karyokinesis • Cytoplasm divides - cytokinesis • Occurs in Somatic (non-sex) cells – sex cells are formed from Meiosis • Both daughter cells have the full 46 chromosomes (Chromosomes were replicated in S-phase)

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46 chromosomes in each cell

• Chromosomes are diploid pairs = • 23 paternal (father) • 23 maternal (mother)


Sister Chromatids

Centromere

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Phases of Mitosis Prophase Metaphase Anaphase Telophase

PMAT


Prophase •Chromatin condenses into chromosomes •Centrosomes move towards opposite poles of cell •Nuclear envelope breaks down •Spindle fibers arise from centrosomes = asters


Figure 3.36b Prophase


Metaphase • Spindle fibers attach to centromeres • Chromosomes align along equator of cell


Anaphase • Spindle fibers shorten & pull on chromosomes • Chromosomes separate & move towards opposite poles of cell


Telophase •Chromosomes complete migration •Nuclear envelopes reform •Chromosomes begin to unwind •Cytokinesis completes


Cytokinesis •Division of Cytoplasm •Begins during Anaphase & continues through Telephase •Microfilament rings pinches off two cells from one



Section 3, Chapter 3: Cells