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