Download The Cell Cycle

The Cell Cycle
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Reproduction
• Asexual Reproduction:
– Involves only 1 organism
– New individual is genetically identical to
parent-clone
• Single celled organisms
–- binary fission: cell divides in 2
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Multicelled organisms:
• Budding
• Plant propagation
• Parthenogenesis
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Reproduction
• Sexual Reproduction:
– Involves 2 parental organisms
– New individual is different from either
parent
– Leads to greater genetic diversity
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• Sexual Reproduction:
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Chromosome Structure
• Chromatin: DNA and protein in long, thin
thread-like, invisible form
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Chromosome Structure
• Chromosomes: Condensed chromatin
that appear right before cell division
– Sister chromatids- contain exact copies of
DNA– Centromere- protein “button” holds
chromatids together
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Chromosome Structure
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The Cell Cycle
• The time it takes from 1 cell division to
the next
• Varies in length of time depending on
cell type
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The Cell Cycle
• Function -asexual reproduction
– Single celled organisms
-produce new individuals– Multicelled organisms –
• Growth -increase in size by increasing in
cell number
• Tissue replacement
and repair
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The Cell Cycle
Two alternating periods
1. Interphase- growth
2. Mitosis- division
Interphase
Growth Division
Mitosis
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Phases of the Cell Cycle
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The Cell Cycle
Interphase:
•
•
•
•
The growth period.
Longest phase of the cell cycle
Cell spends 98% of time in interphase
3 stages
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3 Stages of Interphase
G1 -1st Gap phase:
• The cell grows in size and carries on
normal functions
S - Synthesis phase:
• DNA Replication
• Chromosomes copied in preparation
for cell division.
G2 - 2nd Gap phase:
• Structures needed for cell division are
assembled.
• No turning back- cell division will occur
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Phases of the Cell Cycle
How the Cell
Cycle Works
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The Cell Cycle
• Mitosis:
– The division period
– Division of the nucleus
– Four distinct phases.
• Prophase
• Metaphase
• Anaphase
• Telophase
The Cell Cycle
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Prophase
• First phase of mitosis
• Chromatin condenses and chromosomes
become visible
• Nuclear membrane and nucleoli
disappear
• Structures necessary for cell division appear
– Centrioles- barrel shaped, 2 pair, each
moves to opposite poles
– Spindle fibers- span the two poles
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Prophase
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Metaphase
• Chromosomes line up along the midline
of the cell
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Anaphase
• Centromeres and sister chromatids
separate
• Spindle fibers shorten and pull chromatids,
now called chromosomes, toward opposite
poles
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Telophase
• Reverse of Prophase
• Begins when chromosomes stop after
reaching poles
• Chromosomes decondense to less visible
chromatin form
• Nucleoli reappear
• Nuclear membrane appears around each
set of chromosomes
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Telophase
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Cytokinesis
Division of the cytoplasm and organelles
Results in 2 daughter cells
New cells begin a new cell cycle
Different for plants and animals
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Animal Cell Cytokinesis
Cleavage furrow-cell membrane pinches in
Animation: Mitosis
Mitosis
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Plant Cell Cytokinesis
Cell plate formation- new cell wall is added
to separate 2 daughter cells
onion root tip
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Control of the Cell Cycle
• A series of enzymes monitor a cell’s
progress from phase to phase.
• A disrupted cell cycle can result in
excessive cell division, or cancer
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Skin Cancers
Benign
Malignant
Symmetrical
Asymetrical
Borders are even
Borders are uneven
One shade
Color:Two or more
shades
Smaller than 1/4 inch
Diameter: Larger
than ¼ inch
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http://www.skincancer.org/skin-cancer/melanoma/melanoma_2.html