Chromosomes and Cell Division
DNA

Negatively charged

Double stranded

Wraps around histones

CHROMOSOME=chromatid + kinetochore

46 chromosomes in humans
DNA Limits Cell Size


Cell cannot survive unless there is
enough DNA to support the protein
needs of the cell
Some really large cells are multinucleated
› More nuclei =
› more DNA =
› quick protein making
Cell Reproduction
Cell Division= making 2
daughter cells from one
parent cell
AKA : Asexual Reproduction
Happens in all cells
New cells are genetically
identical!
Prokaryote
Cell Division
Bacteria
 Circular DNA
 Produce 2
daughter cells
by BINARY
FISSION
 DNA copied
 Know steps!

How do little elephants grow up to be BIG
elephants?
The process of mitosis begins
after a sperm fertilizes an egg.
Only happens in eukaryotes.
Only happens in somatic cells.
Cells reproduce constantly.
Skin cancer - the abnormal growth of
skin cells - most often develops on skin
exposed to the sun.
Animated Mitosis Cycle
http://www.cellsalive.com/mitosis.htm
• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase & Cytokinesis
Chromosomes are copied (# doubles)
• Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome
and its copy(sister chromosome) change to sister
chromatids at end of this phase
•
Nucleus
CELL
MEMBRANE
Cytoplasm
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
•
•
Mitosis begins (cell begins to divide)
Centrioles appear and begin to move to
opposite end of the cell.
Spindle fibers form between the poles.
Nuclear membrane breaks down.
Centrioles
Sister chromatids
Spindle fibers
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
•
•
•
Meta = Middle
Centromere/Kinetochore replicate
Sister Chromatids (or pairs of chromosomes)
attach to the spindle fibers.
Chromosomes line up along the equator
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Chromatids (or pairs of chromosomes)
separate and are pulled to the poles
• Pulled by spindle fibers.
•
Centrioles
Spindle fibers
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Two new nuclei form.
• Nuclear Membrane reforms
• Spindle Fibers fall apart
• Chromosomes uncoil into chromatin (thread)
• Cleavage: membrane pinches to make 2
identical cells (Cytokinesis)
•
Nuclei
Chromatin
Nuclei
Animal Cell
Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
•
Cell membrane moves inward to create two
daughter cells – each with its own nucleus
with identical chromosomes.
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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- Cell Division
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Why is mitosis important?
Growth and replacement of
dead, lost, or damaged cells
Ensures each daughter cell
gets a complete and exact
copy of the genetic material
from the parent cell in the
quickest, most efficient way
http://www.cellsalive.com/mitosis.htm
 Means
division of the cytoplasm
 Division of cell into two,
identical halves called daughter
cells
 In plant cells, cell plate forms
at the equator to divide cell
 In animal cells, cleavage furrow
forms to split cell
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28
Cleavage furrow
in animal cell
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Cell plate in plant
cell
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Two
identical
daughter
cells
Parent Cell
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If mitosis is not
controlled, unlimited
cell division occurs
causing cancerous
tumors
 Oncogenes are
special proteins that
increase the chance
that a normal cell
develops into a
tumor cell

Cancer cells
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