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Mitosis
Why do cells divide?
(Purpose of Mitosis)
• Growth
• Repair and replace dead cells
• asexual reproduction
What cells divide often?
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Skin
Stomach lining
Red Blood cells
Embryo
Plant roots
Hair
Nails
What cells rarely/never
divide?
• Nervous System (nerve cells)
• Liver (liver cells)
Interesting Fact:
Why do we age?
• Eventually cells stop being replaced
• “Apoptosis”
– Cell death
• “We die because our cells die.”
– William R. Clark
“C” Terms
• Chromosomes
– Long threads of genetic
material
– Found in nucleus
• Chromatid
– One side of a duplicated
chromosome
“C” Terms
• Centromere
– Structures that
hold sister
chromatids
together
• NOTE
– 2 sister
chromatids = 1
duplicated
chromosome
• DNA is broken into long strands and
wrapped around proteins to form
structures called chromosomes.
“C” Terms…
• Centrioles
– Small protein bodies
– In cytoplasm
– Animal cells only
– Spindle fibres extend
from centrioles.
Micrograph of a Chromosome
Cell Reproduction
• Cells must divide to increase the
number of body cells (not egg or sperm)
in an organism
• There are two parts to it:
– mitosis - the division of the nuclear material
– cytokinesis - the division of the cytoplasm
and organelles
Cell Division in a Nutshell
• Before:
– Chromosome duplicates = 2 sister
chromatids (DNA replication  )
• During:
– Sister chromatids separate
• After:
– 2 “daughter” cells
– Genetically identical
Mitosis Phases
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Interphase
Prophase
Metaphase
Anaphase
Telophase
Stages of Mitosis: Interphase
• resting phase (period between divisions)
• centrioles are just outside the nuclear
membrane
• nucleolus is present and DNA appears as
fine threads called chromatin
• DNA replicates and appears as double
chromosomes and centrioles begin to move
apart near the end of this phase
Interphase
membrane
Stages of Mitosis: Prophase
• nucleolus disappears
• centrioles move to opposite sides of
nucleus
• asters and spindle fibers form around each
centriole
• nuclear membrane disappears
• chromosomes are visible as two sister
chromatids held together at the centromere
Prophase
Spindle fiber
membrane
Stages of Mitosis: Metaphase
• chromosomes line up along equator
(middle) of cell
• spindle fibers extend from centrioles (poles)
to centromeres of the paired chromatids
Metaphase
Stages of Mitosis: Anaphase
• chromatids separate and move toward
opposite poles
Anaphase
Stages of Mitosis: Telophase
• chromosomes disappear; chromatin
reappears
• spindle fibers and asters disappear
• nucleolus reappears and nuclear
membrane reforms
• cell membrane pinches inward to split
cytoplasm (cytokinesis)
Telophase & Cytokinesis
Cytokinesis…
Concept Map
Mitosis Animation
Mitosis in Plants
• Mitosis in plants is very similar to
animals with 2 exceptions:
– plant cells lack centrioles
– plant cells form a cell plate between
the two daughter cells in telophase.
Cytokinesis in Plants
Cytokinesis
• Why would it occur differently in animal
and plant cells?
• Plant cells have a rigid cell wall!
Cytokinesis
Animal Cells
• Cell membrane
pinches inward
• Creates cleavage
furrow
• Think:
– Pull a string around a
balloon
Plant Cells
• Cell Plate forms
between two new
nuclei
• Becomes cell wall
What phases do you see?
A
C
B
D
What phase?
Interphase
What phase?
Prophase
What phase?
Metaphase
What phase?
Anaphase
What phase?
Telophase
What phase?
Interphase
Understanding Concepts
1) Go to page 90 in BIOLOGY 11 BOOK
- Answer questions 2, 3, 4, 5, 6, 7, 9, 10
2) Complete Mitosis Review Worksheet