Transcript RTW Wednesday, November 13th

Ch. 5.2- Mitosis & Cytokinesis
Mitosis “The Movie”
Phases of the Cell Cycle
• The cell cycle consists of
▫ Interphase – normal cell activity
▫ The mitotic phase – cell division
Functions of Cell Division
100 µm
(a) Reproduction. An amoeba,
a single-celled eukaryote, is
dividing into two cells. Each
new cell will be an individual
organism (LM).
200 µm
20 µm
(b) Growth and development. (c) Tissue renewal. These dividing
This micrograph shows a
bone marrow cells (arrow) will
sand dollar embryo shortly after
give rise to new blood cells (LM).
the fertilized egg divided, forming
two cells (LM).
Chromosome
• = one long continuous thread of DNA that
consists of numerous genes & regulatory info.
▫ Your body cells have 46 chromosomes
 23 from Mom & 23 from Dad
• DNA wraps around proteins (histones) to keep
it condensed and organized
Chromosomes
• Chromatins becomes more condensed as a cell
goes into mitosis
• Chromatid= one half of the duplicated
chromosome
▫ 2 chromatids= sister chromatids
▫ The centromere holds the sister chromatids
together
• Telomers= are at the ends of DNA molecules &
protect the genes from damage
Mitosis
• 4 phases of mitosis
• Occurs in body cells resulting in two genetically
identical nuclei
• After mitosis, cytokinesis (splitting of
cytoplasm) occurs
Prophase
•
•
•
•
Chromatid condenses
Nuclear envelope breaks down
Nucleolus disappears
Centrosomes and centrioles
migrate to opposite ends of the
cell
• Spindle fibers start to grow
PROPHASE
Aster
Early mitotic
Centromere
spindle
Chromosome, consisting
of two sister chromatids
Metaphase
• Spindle fibers attach to each
chromosome
• Chromosomes align along the
cell equator (metaphase plate)
Spindle
METAPHASE
Metaphase
plate
Centrosome at
one spindle pole
Anaphase
• Sister chromatids separate
• Spindle fibers shorten
which pulls sister
chromatids away from each
other & towards opposite
ends of the cell
ANAPHASE
Daughter
chromosomes
Telophase
• Complete set of identical
chromosomes are at each
pole of the cell
• Nuclear membrane starts to
form
• Chromosomes begin to
uncoil
• Spindle fibers fall apart
TELOPHASE AND CYTOKINESIS
Cleavage
furrow
Nuclear
envelope
forming
Nucleolus
forming
Cytokinesis
• Cytoplasm divides into two cells and completes a
full stage of the cell cyle
• Different in plant & animal cells
▫ Animal cells- the membrane furrows
▫ Plant cells- a cell plate forms since the cell wall is
too rigid for the cell to furrow (or pinch together)
Cleavage furrow
Contractile ring of
microfilaments
100 µm
Vesicles
forming
cell plate
Wall of
patent cell
1 µm
Cell plate
New cell wall
Daughter cells
Daughter cells
(a) Cleavage of an animal cell (SEM)
(b) Cell plate formation in a plant cell (SEM)