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Mitosis
Importance of Mitosis
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Growth, repair, and asexual reproduction (meiosis is sexual repro)
Mitosis passes a complete genome from the parent cell to daughter cells.
Mitosis followed by cytokinesis produces two genetically identical daughter cells.
Occurs AFTER DNA replication
Mitosis takes place in our body over two trillion times per day!
Cytokinesis: when the
two cells physically
separate
Mitosis vs. Binary Fission
• Mitosis is for eukaryotes and binary fission is for prokaryotes
• In order for the word ‘mitosis’ to be used for cell division
there needs to be the presence of a nucleus
Asexual reproduction in Eukaryotes
• Reproduction by which offspring arise from a single
organism, and inherit the genes of that parent only
• Occurs in similar organisms
• Ex. Running in strawberry plants or bamboo
• Ex. Grafting of plants
• Ex. Budding in hydra
The Biggest Organism on Earth
Ploidy
• Every cell in our body is diploid – one chromosome
from mom, one from dad
• Remember, we have 23 PAIRS of chromosomes
• That means we have TWO versions of every gene
• Mitosis produces diploid cells
The Players
• Nucleus
• Chromosomes
• Spindle fibers
• Centromeres
• Centrioles
• What happens to each of these players throughout the mitotic process?
• What happens when?
• 4 phases of nuclear division (mitosis), directed by the cell’s DNA
(PMAT)
Prophase
Metaphase—(Middle)
Anaphase—(Apart)
Anaphase—(Apart)
Telophase—(Two)
Prophase
 Chromosomes coil up
 Nuclear envelope
disappears
 Spindle fibers form
Metaphase—(Middle)
 Chromosomes line up in
middle of cell
 Spindle fibers connect to
chromosomes
Anaphase—(Apart)
 Chromosome copies
divide
 Spindle fibers pull
chromosomes to opposite
poles
Telophase—(Two)
 Chromosomes uncoil
 Nuclear envelopes form
 2 new nuclei are formed
 Spindle fibers disappear
Cytokinesis — the division of the rest of the cell (cytoplasm and
organelles) after the nucleus divides
In animal cells the cytoplasm
pinches in
In plant cells a cell plate forms
•After mitosis and cytokinesis, the cell returns to Interphase to
continue to grow and perform regular cell activities
Again…
The Life of a Cell
The Cell Cycle
Cell Cycle
• G0 = silence, not growing/dividing
• G1 = getting ready for DNA synthesis
• S = “Synthesis of DNA”
• During S phase we duplicate each chromosome
meaning we have 2 from mom and 2 from dad =
tetraploidy (4n)
• G2 = getting ready for mitosis
Reminder – structure of a chromosome
Sister
Steps in Mitosis
1. Chromosomes condense into chromatin
- 50% protein (histone), 50% DNA
- The two copies are called “sister chromatids”
- Centromere: region where sister chromatids are held together
- Kinetochore: a specialized structure on the centromere to which the spindle fibers attach
during mitosis and meiosis
2. Nuclear envelope disintegrates
3. Spindle fibers begin forming from centrioles as centrioles begin migrating to
either pole of the cell
Steps in Mitosis
4. Centrioles have migrated to
poles and their spindle fibers have
grown and attached to the
kinetochore’s located at the
centromere of the chromosomes
(prometaphase)
Steps in Mitosis
5. The spindle fibers assist in lining the chromosomes up in the middle
of the cell (metaphase = middle)
Steps in Mitosis
6. What this says…
Anaphase = Apart
Steps in Mitosis
7. Telophase – the opposite of prophase
- the nuclear envelope reappears
- the chromosomes decondenses
- the spindle fibers shrink back and the centrioles just go back to
hanging out in the cells cytoplasm
8. Cleavage of the two cells (not technically part of mitosis, but is called
cytokinesis)
Cytokinesis
1. Replication (DNA Synthesis)
2. Alignment (Mitosis)
We are here
3. Separation (Cytokinesis)
- the literal splitting of one cell that has undergone DNA
replication and mitosis into two cells