Cell Division
Continuity of Life
Common Features of all types of
cell division
• DNA replication must
occur prior to cell
division
• DNA must be
distributed to
daughter cells
• Daughter cells
contain equivalent
quantities of DNA
Types of cell division
• Binary fission
– Occurs in Prokaryotic organisms
– Purpose- growth in numbers
• Mitosis
– Occurs in most eukaryotic cells
– Purpose- growth in numbers
– Maintains chromosome number
• Meiosis
– Occurs in germ cells
– Purpose- produce haploid cells
Binary Fission
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Simple process
Single chromosome
Duplication of DNA
Invagination of plasma
membrane
• Formation of daughter
cells
• Time frame- 15 minutes
to several hours
• Video
Mitosis
• Form of nuclear division
• Complex process
• Several linear chromosomes
involved
• Chromosome number
maintained
• 4 major steps required
• Steps result in appropriate
distribution of chromosomes
• Mechanism of growth for most
eukaryotic cells
• Carried out in somatic cells
Steps in Mitosis
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Interphase
Prophase
Metaphase
Anaphase
Telophase
(Cytokinesis)
Prophase
• Chromosomes condense
• Centrosome (may contain
centriole) duplicates
• Nuclear envelope breaks
up
• Spindle fiber forms from
microtubules
• Chromosomes hooked
onto spindle fibers
Chromosome Structure
Condensed DNA
Metaphase
• Spindle fibers pull
chromatids in
opposite directions
• Chromosomes align
at the cell equator
• Concludes when
chromatids separate
Anaphase
• Chromatids now
unduplicated
chromosomes
• Chromosomes move
to opposite poles of
the cell
• Concludes when
chromosomes reach
opposite poles
Telophase
• Chromosomes
decondense
• Nuclear envelope
reforms
• Cytokinesis usually
begins
Cytokinesis
• Cytoplasmic division
• Animal cells form furrow
by contracting
microfilaments at the
equator
• See text page 133
• Plant cells form a cell
plate by depositing
vesicles containing
cellulose at the equator
• video
Cell cycle
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Interphase
G1- Cell growth
S- DNA replication
G2- Preparation for
mitosis
• M- Mitosis
• G0- waiting mode
• video
Meiosis
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Form of nuclear division
Reduces the chromosome number
by ½
Two stages
– Meiosis I
– Meiosis II
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Crossing over between
homologues
Occurrs in all sexually reproducing
organisms
Produces gametes in most
organisms
Haploid cells
Provides genetic diversity
Stages similar to mitosis
http://www.youtube.com/watch?v=
D1_-mQS_FZ0
Cancer
• Loss of cell growth
control
• No G0
• Check points
transgressed