cell division how cell divide in eukaryotics and pro karyotin systme

1. Cell Division
Eukaryotic and Prokaryotic

2. Overview: The Key Roles of Cell Division
 The ability of organisms to reproduce best
distinguishes living things from non-living matter
 The continuity of life is based upon the reproduction of
cells, or cell division
 Cell division is integral part of cell cycle

3. Cell division is a fundamental
process
 All cells come from pre-existing cells
 It is necessary to replace worn out cells in
multicellular organisms
 It is required for growth in multicellular organisms
 An increase in size will require an increase in surface
area to volume ratio
 Cell division subdivides the cytoplasm into small units
(cells) surrounded by plasma membranes
 It is necessary for reproduction in unicellular or
multicellular organisms
© 2007 Paul Billiet ODWS

4. DNA Replication
The Bacterial Genome
Semiconservative
Replication of DNA
The replication fork of
DNA showing the
synthesis of two
progeny strands. Each
copy contain one new
and one old strand.
Bacterial chromosome is
called Replicon
Replicon – a part of the
genome that contains an
origin site and is replicated
as a whole unit

5. Types of cell division
 Prokaryotes
 Binary fission
 Eukaryotes
 Mitosis:
 Growth, development & repair
 Asexual reproduction (yields genetically identical cells)
 Occurs in somatic (body) cells
 Meiosis:
 Sexual reproduction (yields genetically different cells
with half the # of chromosomes)
 Occurs in specific reproductive cells
 Yields gametes (e.g., eggs & sperm) or spores

6. Prokaryotes
 Prokaryotes have no
nucleus
 They have a single
circular chromosome
 Prokaryotes simply
divide their cells in two
by binary fission
http://instruct1.cit.cornell.edu/
© 2007 Paul Billiet ODWS

7. Binary Fission
 Prokaryotes (bacteria and archaea) reproduce by a
type of cell division called binary fission
 In binary fission, the chromosome replicates
(beginning at the origin of replication), and the two
daughter chromosomes actively move apart

9. Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome
E. coli cell
Two copies
of origin
Chromosome
replication begins.
Soon thereafter,
one copy of the origin
moves rapidly toward
the other end of the cell.

10. LE 12-11_2
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome
E. coli cell
Two copies
of origin
Chromosome
replication begins.
Soon thereafter,
one copy of the origin
moves rapidly toward
the other end of the cell.
Replication continues.
One copy of the origin
is now at each end of
the cell.
Origin Origin

11. LE 12-11_3
Origin of
replication
Cell wall
Plasma
membrane
Bacterial
chromosome
E. coli cell
Two copies
of origin
Chromosome
replication begins.
Soon thereafter,
one copy of the origin
moves rapidly toward
the other end of the cell.
Replication continues.
One copy of the origin
is now at each end of
the cell.
Origin Origin
Replication finishes.
The plasma membrane
grows inward, and
new cell wall is
deposited.
Two daughter
cells result.

12. Eukaryotes
 Eukaryotic cell division consists of:
 Mitosis, the division of the nucleus
 Cytokinesis, the division of the cytoplasm

13. Cellular Organization of the Genetic Material
 A cell’s endowment of DNA (its genetic information) is
called its genome
 DNA molecules* in a cell are packaged into
chromosomes
*Prokaryotes-
circular DNA
Eukaryotes-
linear DNA

14. Cellular Organization of the Genetic Material
 Every eukaryotic species has a characteristic number
of chromosomes in each cell nucleus
 Somatic (non-reproductive) cells (normally) have two
sets of chromosomes
 Gametes (reproductive cells: sperm and eggs) (and
spores) have half as many chromosomes as somatic
cells
 Eukaryotic chromosomes consist of chromatin, a
complex of DNA and protein that condenses during cell
division

15. DNA associates with special proteins to form more stable
structure called chromosomes (different proteins in
prokaryotes and eukaryotes, so chromosomes built different)
Chromosomes are found inside nucleus in eukaryotes
Human - 46 chromosomes, 23 pairs (1 set of 23 from egg, 1
set of 23 from sperm)
Each chromosome contains many genes
Gene is a segment of DNA that is responsible for controlling
a trait (e.g., coding for a specific protein)
Cellular Organization of the Genetic Material

17. Human female karyotype

18. Human male karyotype

19. Eukaryotes
 Eukaryotes must divide their nucleus (and other
organelles such as mitochondria) in preparation for
cell division (mitosis or meiosis)
 Before the nucleus divides the genetic material
replicates (duplicates)
© 2007 Paul Billiet ODWS

20. Mitosis
The process of cell division which results
in the production of two daughter cells
from a single parent cell.
The daughter cells are identical to
one another and to the original parent
cell.

21.  Mitosis is conventionally divided into five phases:
 Prophase
 Prometaphase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis is well underway by late telophase

22. Interphase
The cell prepares for division
 Animal Cell
 DNA replicated
 Organelles replicated
 Cell increases in size
 Plant Cell
 DNA replicated
 Organelles replicated
 Cell increases in size

23. Interphase
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

24. Prophase
The cell prepares for nuclear division
 Animal Cell
 Packages DNA into
chromosomes
 Plant cell
 Packages DNA into
chromosomes

25. Prophase
 Chromatin condenses, this causes the
chromosomes to begin to become visible
 Centrosomes separate, moving to opposite ends of
the nucleus
 The centrosomes start to form a framework used
to separate the two sister chromatids called the
mitotic spindle, that is made of microtubules
 Nucleolus disappears

29. Prophase
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

30. Prometaphase
 Nuclear envelope fragments
 Chromosomes become more condensed
 A kinetochore is formed at the centromere, the point
where the sister chromatids are attached
 Microtubules attach at the kinetochores

32. The Mitotic Spindle: A Closer Look
 The mitotic spindle is an apparatus of microtubules
that controls chromosome movement during mitosis
 Assembly of spindle microtubules begins in the
centrosome, the microtubule organizing center
 The centrosome replicates, forming two centrosomes
that migrate to opposite ends of the cell, as spindle
microtubules grow out from them
 An aster (a radial array of short microtubules) extends
from each centrosome

33. The Mitotic Spindle: A Closer Look
• The spindle includes the centrosomes, the spindle
microtubules, and the asters
• Some spindle microtubules attach to the kinetochores
of chromosomes and move the chromosomes to the
metaphase plate

34. LE 12-7
Microtubules Chromosomes
Sister
chromatids
Aster
Centrosome
Metaphase
plate
Kineto-
chores
Kinetochore
microtubules
0.5 µm
Overlapping
nonkinetochore
microtubules
1 µm
Centrosome

35. Metaphase
The cell prepares chromosomes for
division
 Animal Cell
 Chromosomes line up at
the center of the cell
 Spindle fibers attach from
daughter cells to
chromosomes at the
centromere
 Plant Cell
 Chromosomes line up at
the center of the cell
 Spindle fibers attach from
daughter cells to
chromosomes at the
centromere

36. Metaphase
 Chromosomes align on an axis called the metaphase
plate

 Note: the spindle consists of microtubules, one
attached to each chromosome

38. Metaphase
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

39. Anaphase
 Each centromere splits making two chromatids free
 Each chromatid moves toward a pole
 Cell begins to elongate, caused by microtubules not
associated with the kinetochore

41. Anaphase
The chromosomes divide
 Animal Cell
 Spindle fibers pull
chromosomes apart
 ½ of each chromosome
(called chromotid) moves
to each daughter cell
 Plant Cell
 Spindle fibers pull
chromosomes apart
 ½ of each chromosome
(called chromotid) moves
to each daughter cell

42. Anaphase
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

43. The Mitotic Spindle: A Closer Look
 In anaphase, sister chromatids separate and move
along the kinetochore microtubules toward opposite
ends of the cell
 The microtubules shorten by depolymerizing at their
kinetochore ends

44. LE 12-8b
Chromosome
movement
Microtubule Motor
protein
Chromosome
Kinetochore
Tubulin
subunits

45. The Mitotic Spindle: A Closer Look
 Nonkinetochore microtubules from opposite poles
overlap and push against each other, elongating the
cell
 In telophase, genetically identical daughter nuclei form
at opposite ends of the cell

46. Telophase
The cytoplasm divides
 Animal Cell
 DNA spreads out
 2 nuclei form
 Cell wall pinches in to
form the 2 new daughter
cells
 Plant Cell
 DNA spreads out
 2 nuclei form
 New cell wall forms
between to nuclei to form
the 2 new daughter cells

47. Telophase
• Formation of nuclear membrane and nucleolus
• Short and thick chromosomes begin to elongate to
form long and thin chromatin
• Formation of the cleavage furrow - a shallow
groove in the cell near the old metaphase plate
• Cytokinesis = division of the cytoplasm

49. Telophase
Animal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

50. Mitosis in an onion root

51. Cytokinesis: A Closer Look
 In animal cells, cytokinesis occurs by a process known
as cleavage, forming a cleavage furrow
 In plant cells, a cell plate forms during cytokinesis

52. LE 12-9a
Cleavage furrow
100 µm
Contractile ring of
microfilaments
Daughter cells
Cleavage of an animal cell (SEM)

53. Mitosis

54. LE 12-9b
1 µm
Daughter cells
Cell plate formation in a plant cell (TEM)
New cell wall
Cell plate
Wall of
parent cell
Vesicles
forming
cell plate

55. LE 12-10
Nucleus
Cell plate
Chromosomes
Nucleolus
Chromatin
condensing 10 µm
Prophase. The
chromatin is condensing.
The nucleolus is
beginning to disappear.
Although not yet visible
in the micrograph, the
mitotic spindle is starting
to form.
Prometaphase. We
now see discrete
chromosomes; each
consists of two identical
sister chromatids. Later
in prometaphase, the
nuclear envelope will
fragment.
Metaphase. The spindle is
complete, and the
chromosomes, attached
to microtubules at their
kinetochores, are all at
the metaphase plate.
Anaphase. The
chromatids of each
chromosome have
separated, and the
daughter chromosomes
are moving to the ends of
the cell as their
kinetochore micro-
tubules shorten.
Telophase. Daughter
nuclei are forming.
Meanwhile, cytokinesis
has started: The cell
plate, which will divide
the cytoplasm in two, is
growing toward the
perimeter of the parent
cell.

56. Plant Mitosis -- Review
Interphase Prophase
Metaphase Anaphase
Telophase Interphase

57. Animal Mitosis -- Review
Interphase Prophase
Metaphase Anaphase
Telophase Interphase

60. The Evolution of Mitosis
 Since prokaryotes evolved before eukaryotes, mitosis
probably evolved from binary fission
 Certain protists exhibit types of cell division that seem
intermediate between binary fission and mitosis