The document discusses cell division and the cell cycle. It begins by outlining the key phases of the cell cycle - interphase, mitosis, and cytokinesis. Interphase is further broken down into the G1, S, and G2 phases where the cell grows and duplicates its contents. Mitosis is the phase where the cell nucleus divides into two identical nuclei. Cytokinesis then divides the cytoplasm into two daughter cells. The document also discusses DNA structure and replication, noting the double helix structure and enzymes involved in duplicating DNA. Abnormal cell division can lead to diseases like cancer if the cell cycle is not properly controlled.

1. Cell Division
Mitosis- Cell reproduction

2. Learning Objectives
•
•
•
•
The cell cycle and its phases.
The cell division “mitosis”.
Cell cycle control system.
The different abnormalities of cell cycle
(cancer).
• DNA structure and DNA replication .

3. Key Words
•
•
•
•
•
Chromosome
chromatin
centriole & centrosome
centromere & kinetochore
chromatid
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4. chromosome
A chromosome is a long,
continuous piece of DNA
which contains the
genetic information for a
cell.
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5. chromatin
Chromatin is the building block for a
chromosome. It consists of DNA and
proteins.
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6. Centriole & centrosome
A centriole is a barrel microtubule structure. Two
centrioles arrange themselves perpendicularly to
form a centrosome.
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7. centromere & kinetochore
• The centromere is constricted region of the
chromosomes that holds the sister chromatids
together, the site where kinetochore forms.
• The kinetochore is a complex protein
containing structure to which microtubules
attach.
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8. chromatid
Is a one strand of the
chromosome after it has
duplicated for cellular
division. The two
chromatids are called
“sister chromatids” and
will eventually split and
move to opposite ends
of the cell.
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Sister chromatids
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9. Ready?
Let’s begin
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10. Cell division
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11. Why do cells divide?
•Growth
•Repair and replace dead cells
•asexual reproduction
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12. THE CELL CYCLE
______________________
_

13. • Define cell cycle: the cell cycle is the
sequence of growth and division of a cell.
It consists of three major phases:
o interphase
o mitosis
o cytokinesis.
• Cell division results in two cells that are
both identical to the parent cell.
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14. Interphase
Estimated (90% of cycle)
3 phases
•G1 phase
•S phase
•G2 phase
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15. G1 phase
• Growth of cell.
• Dupliction of organelles.
• Synthisis of proteins.
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16. S phase
• DNA synthesis occurs
• DNA replication results in
duplicated chromosomes
• centrosome cycle
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17. G2 phase
• Cell continues to grow and if a problem
occurs in DNA replication, it will be repaired.
• Cell will prepare for mitosis.
• cell synthesizes proteins needed for cell
division
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18. M phase
Estimated (10% of cycle)
Includes 2 parts :
1)Mitosis
•Prophase
•Promataphase
•Metaphase
•Anaphase
•Telophase
2) Cytokinesis
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19. Mitosis
• is the process in which a eukaryotic cell
separates the chromosomes in its cell
nucleus, into two identical sets in two
daughter cells.
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20. Prophase
Duration (15 min)
• Chromosomes condense (get
thicker) and coil, they become
visible under light microscope.
• The two sister chromatids of each
chromosomes attach at a point
called centromere.
• Spindle fibers begin to form from
two centrosome, and they will start
moving apart.
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21. Prometaphase
Duration (15 min)
• The nuclear membrane
disappears.
• Kinetochores will get attached
to the centromere.
• The spindle fibers become
attached to the kinetochore.
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22. Metaphase
Duration (20 min)
• Chromosomes reach their most
highly condensed state.
• The spindle fibers begin to
contract to the centromeres of
the chromosomes, which are
now arranged along the middle
of the spindle.
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23. Anaphase:
Duration (3 min)
• The centromere of each
chromosome splits, allowing the
sister chromatids to separate.
• The chromatids are then pulled by
the spindle fibers toward opposite
sides of the cell.
• The two sets of chromosomes are
identical.
• Cleavage furrow starts to form.
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24. Telophase:
Duration (10 min)
• New nuclear membranes are formed
around each of the two sets of 46
chromosomes.
• The spindle fibers disappear.
• Chromosomes become thinner.
• Cytoplasm starts dividing by contractile
ring.
• At the end, we will have two diploid
daughter cells, which are identical.
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25. Cytokinesis
•
•
the division of the cytoplasm and
organelles
Begin in anaphase and completed
by the end of telophase .
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27. Summary
•
o
o
o
Interphase (90% of cycle)
G1 phase~ growth
S phase~ synthesis of DNA
G2 phase~ preparation for
cell division
• Mitotic phase (10% of cycle)
o Mitosis~ nuclear division
o Cytokinesis~ cytoplasm
division
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28. Cell cycle control
system

29. Cell cycle control system
Involves
•Cell cycle checkpoints
•Specialized protein complex
Function control the order and timing of the
cell cycle.
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30. Checkpoints
( control points )
They are pathways that:
•Ensure that events are completed correctly before
letting the cell enter the next phase.
The checkpoint receive signals from :
inside and outside the cell
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31. Checkpoints
There are 3 major checkpoints :
I.at the end of G1
it is large & strong enough to continue with the cell division process
II.at the end of G2
III. during mitosis phase
it ensures if the spindles attached to the kinetochore within each
chromosome
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33. Specialized
protein complex
Is a combination of a Cycline & Cdk*
to preform its work ( help the cell to enter the next phase) it
has to be activated by phosphorylated at one site and
dephosphorylated at the other site.
kinase
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* Cycline dependent
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34. Now we’ll see how much you’ve
learned
so raise your hand
and wait your turn...
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35. Cell Cycle
interphase
M
I
T
O
S
I
S
Chromosomes appear, nucleus
disappears
prophase
Chromatids pulled to poles
metaphase
Chromosomes invisible; DNA replicates
anaphase
Cytoplasmic division
telophase
Chromosomes at equator, spindle
forms
cytokinesis
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Chromatids at poles, nucleus reforms
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36. Cell Increase and Decrease
•
Cell division:
o Mitosis
o Cytokinesis
•
Apoptosis (cell death) decreases the number
of cells.
•
Both cell increase and apoptosis occur
during normal development and growth.
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37. Abnormal Division

38. Abnormalities
• If there is a damage in DNA during G1 and the P53
is not present, the cell can’t stop entering into the
next phase so, it will complete the cycle in an
abnormal way.Then the cycle will be uncontrolled .
• If a cell has extra protein BCL2 then it can absorb
all of the death signals so the cell will prevent
death(apoptosis) .That will leads to a high rate of
mutation and the production of cells that tend to
become cancerous ( tumor ) .
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39. • The uncontrolled growth of
cells in human to the
disease called cancer.
http://www.youtube.com/watch?v=vKIRWY-LMYc

40. • The uncontrolled growth of
cells in human to the
disease called cancer.
http://www.youtube.com/watch?v=vKIRWY-LMYc

41. DNA

42. DNA & Mitosis
• Before:
– Chromosome duplicates = 2 sister chromatids
(DNA replication )
• During:
– Sister chromatids separate
• After:
– 2 “daughter” cells
– Genetically identical
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43. DNA structure
• Two strands coiled called a
double helix.
• Center made of nitrogen
bases bonded together by
weak hydrogen bonds.
• Stands for
deoxyribonucleic acid
made up of subunits called
nucleotides.
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44. constituents of nucleotide
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45. Nucleotide made of:
• Phosphate group
• 5-carbon sugar
• Nitrogenous base
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46. Anti-parallel Strands
•One strand of DNA
goes from 5’ to 3’
•The other strand is
opposite in direction
going 3’ to 5’
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47. DNA Replication

48. Models of DNA replicate?“Possibilities”
In this model , one
daughter molecule
contains both parental
DNA strands, and the
other daughter molecule
contains DNA strands of
all newly-synthesized
material.
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In this model two
DNA double helices,
both of which consist
of one parental and
one new strand.
In this model the
parental double helix is
broken into doublestranded DNA
segments .The
segments assemble into
complete DNA double
helices from new and
parental strands
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49. Steps of DNA replication
1. The DNA strands are separated at a
specific area called origin .
2. The complementary strands are synthesized
by DNA polymerase .
3. Termination : DNA polymerase goes
throughout each strand in order to find errors
and correct them.
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50. Base pairing During Replication

51. Enzymes Required for Replication
• Helicase: an enzyme that catalyzes the energy-dependent
unwinding of the DNA double helix during DNA replication.
• DNA polymerase: an enzyme that catalyzes the assembly of
deoxyribonucleoside triphosphates into deoxyribonucleic acid, with
single-stranded DNA serving as the template. The enzyme is often
found in tumor cells.
• Ligase : Joins together small newly synthesized pieces of DNA
called Okazaki fragments.
• Primase : Adds an RNA primer so that DNA synthesis can begin
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52. Bayan Al-Ghadeer
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53. Summary
 Abnormal division
• What happens when DNA is damaged?
 DNA Structure
• constituents of nucleotides.
 DNA Replication
• Models of DNA replication.
• Steps
• Enzymes Required for Replication.
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55. References
• Essential cell biology – third edition
• http://www.biologie.uni-hamburg.de/b-online/library/fal
• http://www.phschool.com/science/biology_place/biocoa