Mitosis is the process by which cells divide. It begins with the duplication of DNA and packaging of the DNA into chromosomes. The cell then undergoes several stages - prophase, metaphase, anaphase and telophase - where the chromosomes align, separate, and are divided between two daughter cells. Cytokinesis then completes the process by physically dividing the cytoplasm and organelles between the two new cells. Careful regulation ensures cells only divide when needed for growth, development, or repair.

1. Mitosis
Biology is the only
subject in which
multiplication is the
same thing as division…

2. Where it all began…
You started as a cell smaller than
a period at the end of a sentence…

3. And now look at you!
How did you
get from
there to
here?

4. Mitosis!
 The fertilized egg must divide…
and divide….
and divide….
and divide…

5. Why do cells divide…
 for reproduction
 one celled organisms (clones)
 asexual reproduction amoeba
 for growth & development
 from fertilized egg to multi-celled organism
 for repair
starfish
 replace cells that die from
normal wear & tear or from injury

6. Dividing cells…
 What has to be copied
 DNA
 organelles
 cell membrane
 lots of other
molecules
• enzymes
plant cell animal cell

7. Copying DNA
 A dividing cell duplicates its DNA
 creates 2 copies of all DNA
 sends the 2 copies to opposite ends of the
cell
 splits into 2 daughter cells
 the DNA starts
DNA
loosely wound in
cell the nucleus
 If you tried to divide
it like that, it could
nucleus tangle & break

8. Organizing & packaging DNA into
chromosomes…
DNA
cell
nucleus DNA has been
“wound up”
DNA in chromosomes in
everyday “working” cell cell
nucleus
4 chromosomes DNA in chromosomes in cell
in this organism getting ready to divide

9. Important
Vocabulary
•DNA
•Chromatin
•Histone
•Chromosomes/
chromatid
•Sister chromatid
•Centromere

10. Structure of a Chromosome

11. Chromosome

12. Copying & packaging DNA
 When cell is ready to divide…
 copy DNA first, then…
 coil up doubled chromosomes
like thread on a spool…
• now can move DNA around cell without having it
tangle & break
Coil DNA into
Copying DNA compact chromosomes

13. Copying DNA…
chromosomes in cell
DNA in chromosomes
cell 4 single-stranded chromosomes
duplicated chromosomes
nucleus
duplicated
chromosomes cell
4 double-stranded chromosomes
nucleus

14. double-stranded
human chromosomes
ready for mitosis

15. Chromosomes of Human Female
46 chromosomes
23 pairs

16. Chromosomes of Human Male
46 chromosomes
23 pairs

17. Cell Cycle

18. Mitosis Vocabulary
 Centrioles – small, cylinder shaped structures found near
the nucleus, involved in mitosis
 Only in animal cells
 Aster – star like structure made of microtubules that
extend from centrioles
 Spindle – web like structure made up of microtubule
fibers. It arranges and moves the chromosomes around.

19. Interphase  DNA found as chromatin
 Cell grows & produces
more molecules &
organelles
 DNA and centrioles
replicate
DNA  Three mini stages:
 G1
cell
 S
 G2
nucleus
Interesting things
happen!

20. Eukaryotic chromsome replicating

21. Prophase
 Chromosomes become
visible
 DNA is wound into
chromosomes
 Nuclear membrane and
duplicated
nucleolus breakdown
chromosomes  Centrioles move to
opposite poles
 Spindle and asters
cell begins to form
Chromosomes
nucleus pair up!

22. Metaphase
 Spindle is fully developed
 Sister chromatids line up
at the equator
 Chromatids are attached
to the spindle at the
centromere
Chromosomes
meet in the
middle!

23. Anaphase  Sister chromatids
separate
 One complete set of
chromosomes goes to
each pole
 Spindle pull chromatids
to opposite poles
 Cytokinesis begins
Chromosomes get
pulled apart!

24. Telophase  Chromosomes reach
opposite poles
 Nuclear membrane and
nucleolus reappear
 Spindle disappears
 Chromosomes unravel
 Cytokinesis is completed
Now there are
two!

25. Cytokinesis
Division of the cytoplasm &
organelles into two cells that
occurs at the end of mitosis

26. New “daughter” cells
 Get 2 exact copies of original cells
 same DNA
 “clones”

27. REMEMBER!
Interphase
Prophase
Metaphase IPMAT
Anaphase
Telophase

28. Mitosis in whitefish embryo

30. How does mitosis differ in plants?

31. How does mitosis differ in plants?
 Plant cells do not have centrioles
 Plant cells do not pinch in half
 Cytokinesis is accomplished through the
formation of a cell plate between the two
daughter cells

32. Overview of mitosis
Copy DNA Wind Up
Bye-Bye!
Line Up Separate Divide

33. onion root tip

34. Cell Turnover – the speed of
mitosis
 The time it takes for a cell to
complete one cycle can vary
between a couple of minutes to
days.
 Cells that are continuously being
worn away have a rapid turnover.
E.g. skin, epithelial cells, RBC, etc.
 Cells which make up organs such as
the eye and the brain do not multiply
very often if ever once they reach
adult size.

35. Control of the Cell Cycle
 Growth & division are carefully regulated
 The protein cyclin regulates the cell cycle.
 Cyclin is produced during interphase.
 Once the cyclin reaches a certain level it
triggers mitosis.
 During mitosis most of the cyclin
is destroyed.
 The new daughter cells must
produce new cyclin before a
second mitosis can occur

36. How do we know?
 Scientists found that when cyclin is
injected into a nondividing cell, that cell
forms a spindle
 They then found the amount of cyclin
increased and decreased in timing with
the cell cycle

37. Other Regulatory Proteins
 Internal
 Proteins in the cell respond to events inside
the cell
• E.g. makes sure cell does not enter mitosis until all
chromosomes have been replicated
• E.g. No anaphase until all chromosomes are
attached to the spindle

38. Other Regulatory Proteins
 External
 Proteins that respond to events outside the
cell
• May stimulate growth – e.g. wound healing,
embryonic development
• May slow growth – e.g. prevent excessive growth,
keep tissues from disrupting each other

39. Cancer – cell division gone wild!
 Cancer – uncontrolled
mitosis
 Don’t respond to normal
cellular controls
 Cells divide excessively
 Many causes resulting in
gene mutations (often in
gene p53)
• Smoking, radiation, viral
infection, heredity

40. Cancer – cell division gone wild!
 Tumor – a mass of abnormal cells
 Benign tumor – abnormal cells remain in
original location
 Malignant tumor – abnormal cells leave the
original site and impair the function of one or
more organs

41. Biology is the only subject in
which multiplication is the same
thing as division…
2006-2007