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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)


46 chromosomes in each cell

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

Sister Chromatids



Phases of Mitosis Prophase Metaphase Anaphase Telophase


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