1. Essentials of Biology Sylvia S. Mader
Chapter 8
Lecture Outline
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2. 8.1 The Basics of Cellular Reproduction
Multicellular organisms begin life as a single cell
We become trillions of cells because of cellular reproduction
Continues as we grow and replace worn-out or damaged tissues

3. Figure 8.1 Cellular reproduction
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c. Amoebas reproduce
b. Tissues repair
a. Children grow
d. Zygotes develop
a: © Corbis RF; b(tail): © McDonald Wildlife Photography/Animals Animals; b(lizard): © Kevin Hanley/Animals Animals; c: © Biophoto Associates/Photo Researchers, Inc.; d(left): © Anatomical Travelogue/Photo Researchers, Inc.; d(right): © Brand X Pictures/PunchStock

4. All cells come from cells
Asexual reproduction
Doesn’t require sperm or egg
Required in sexual reproduction
All cells come from cells
Cellular reproduction is necessary for production of both new cells and new organisms
2 important processes
Growth – cell duplicates its contents (including DNA and organelles)
Cell division – parent cell contents divided into two daughter cells
Both processes heavily regulated

5. Chromosomes Chromatin DNA replication is the copying of DNA
Full set passed to each daughter cell
DNA packaged into chromosomes
Thickened complex of DNA and proteins
Allows easier distribution to daughter cells
Chromatin
DNA and associated proteins have appearance of thin threads

6. DNA periodically wound around histones to form nucleosomes
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Chromosome: duplicated and condensed
DNA periodically wound around histones to form nucleosomes
Just before cell division, chromatin condenses into chromosomes
Humans have 46 chromosomes
sister
chromatids
centromere ×
8,400
looped
chromatin
zigzag
Chromatin: beads-on-a-string
chromatin
nucleosomes
histones
Figure 8.2
Chromosome
compaction
(chromatin): Courtesy O.L. Miller, Jr. and Steve L. McKnight; (chromosome): © Biophoto Associates/Photo Researchers, Inc.

7. Duplicated chromosomes composed of sister chromatids joined at centromere
Each sister chromatid has identical DNA
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duplicated
chromosome
chromosome
consisting
of one
chromatid
duplication
centromere
sister
chromatids
Figure 8.4

8. 8.2 The Cell Cycle
Orderly sequence of stages that takes place between the time a new cell has arisen and to the point where it gives rise to two daughter cells
Interphase
M (Mitotic) Stage

9. Figure 8.3 The cell cycle Interphase Growth occurs as
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Growth occurs as
organelles double. G0 G1
cytokinesis
telophase M
anaphase
Interphase
metaphase
Mitosis and
cytokinesis
occur.
prophase G2 S
Growth occurs
as cell prepares
to divide.
DNA replication
occurs as
chromosomes
duplicate.

10. Interphase Majority of the cell cycle
Time when a cell performs its usual functions
Amount of time varies widely depending on cell
3 stages G1
S – DNA synthesis G2

11. Interphase 3 stages G1 – stage before DNA replication
Cell doubles organelles
Accumulates materials for DNA synthesis
Makes decision whether to divide or not
G0 – arrested – does not go on to divide
S – DNA synthesis
Results in each chromosome composed of two sister chromatids
G2 – stage following DNA synthesis
Extends to onset of mitosis
Synthesizes proteins needed for cell division

12. M (mitotic) phase Cell division occurs Encompasses
Division of nucleus (mitosis)
Creates two identical daughter nuclei
Division of cytoplasm (cytokinesis)

13. 8.3 Mitosis and cytokinesis
Distributes duplicated nuclear contents of parent cell equally to daughter cells
Each sister chromatid has the same genetic information
Daughter chromosomes – separated sister chromatids
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duplicated
chromosome
chromosome
consisting
of one
chromatid
duplication
mitosis
centromere
sister
daughter
Figure 8.4 Overview of mitosis
chromatids
chromosomes

14. Daughter nuclei produced by mitosis are genetically identical to each other and the parent nucleus.
Every animal has an even number of chromosomes – each parent contributes half of the chromosomes to the new individual.
In drawings, colors may be used to indicate chromosomes contributed by the male or female parent.

15. Spindle
Most eukaryotic cells rely on this structure to pull chromatids apart.
Part of cytoskeleton
Spindle fibers are made of microtubules
Centrosome – primary microtubule organizing center
Spindle fibers may overlap at the spindle equator or attach to duplicated chromosomes.

16. Mitosis is a continuous process Traditionally divided into 4 phases
Prophase
Metaphase
Anaphase
Telophase
Plant and animal cells differ
Plant – have centrosomes but lack centrioles
Animal – each centrosome has 2 centrioles and an aster (array of microtubules)

17. Courtesy Dr. Andrew S. Bajer, University of Oregon
Figure 8.5 Mitosis in a plant cell
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condensing
chromosomes
nucleus
with
chromatin
Interphase 5
Prophase 5
chromosomes
spindle equator
Metaphase 5
Courtesy Dr. Andrew S. Bajer, University of Oregon

18. Courtesy Dr. Andrew S. Bajer, University of Oregon
Figure 8.5 Mitosis in a plant cell (continued)
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spindle fibers
(pink)
pole
Anaphase ×5 T
elophase ×5
Courtesy Dr. Andrew S. Bajer, University of Oregon

19. Phases of mitosis in animal cells
Although mitosis is divided into phases, it is a continuous process.
DNA has been replicated before mitosis begins.
Each chromosome consists of 2 sister chromatids attached at a centromere.
Red chromosomes are from one parent, blue are from the other parent.
Mitosis is usually followed by cytokinesis
Division of the cytoplasm
Begins during telophase and continues after the daughter nuclei have formed

20. Figure 8.6 Phases of mitosis in animal cells
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Cell cycle G1, S, G2
Cell cycle M: Phases of mitosis
Interphase
Prophase
250
250
chromosomes
early mitotic spindle
centrioles in
centrosomes
nucleolus
centrosome
spindle
fibers
chromatin
centromere
nuclear
envelope
fragments
nuclear
envelope
chromosome,
consisting of
two sister
chromatids
plasma
membrane
Interphase
During interphase, the eukaryotic
cell duplicates the contents of the
cytoplasm, and DNA replicates in
the nucleus. The duplicated
chromosomes are not yet visible.
A pair of centrosomes is outside
the nucleus.
Prophase
During prophase, the chromosomes are
condensing. Each consists of two sister
chromatids held together at a centromere.
Outside the nucleus, the spindle begins to
assemble between the separating
centrosomes.
Prophase continues with the
disappearance of the nucleolus and the
breakdown of the nuclear envelope.
Spindle fibers from each pole attach to the
chromosomes at specialized protein
complexes on either side of each
centromere. During attachment, a
chromosome first moves toward one pole
and then toward the other pole.
Figure 8.6 Phases of mitosis in animal cells
(all): © Ed Reschke

21. Figure 8.6 continued 21 Phases of mitosis Metaphase Anaphase T
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Phases of mitosis
Metaphase
Anaphase T
elophase and Cytokinesis
aster
×250
×250
×250
chromosomes
at spindle
equator
daughter chromosomes
cleavage furrow
spindle
nucleolus
forming
pole
nuclear
envelope
forming
Metaphase
During metaphase, the
chromosomes are aligned at the
spindle equator midw ay between
the spindle poles. The spindle
fibers on either side of a
chromosome extend to opposite
poles of the spindle. Unattached
spindle fibers reach beyond the
equator and overlap.
Anaphase
During anaphase, the sister chromatids
separate and become daughter
chromosomes. As the spindle fibers
attached to the chromosomes
disassemble, each pole receives a set of
daughter chromosomes. The spindle
poles move apart as the unattached
spindle fibers slide past one another. This
contributes to chromosome separation.
Telophase and Cytokinesis
During telophase, the spindle disappears as
new nuclear envelopes form around the
daughter chromosomes. Each nucleus
contains the same number and kinds of
chromosomes as the original parent cell.
Remnants of spindle fibers are still visible
between the two nuclei. Division of the
cytoplasm begins.
(all): © Ed Reschke
Figure 8.6 continued 21

22. Cytokinesis in animal and plant cells
Accompanies mitosis in most but not all cells
Mitosis with cytokinesis results in a multinucleated cell
Muscle cells in vertebrate animals
Embryo sac in flowering plants

23. Animal cells Cleavage furrow forms as anaphase ends
Contractile ring, band of actin filaments, forms a constriction
Like pulling a drawstring
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cleavage furrow
contractile ring
Figure 8.7 Cytokinesis in animal cells

24. © B.A. Palevitz and E.H. Newcomb/BPS/Tom Stack & Associates
Plant cells
Rigid cell wall prevents furrowing
Involves building of new plasma membrane and cell walls between daughter cells
Golgi apparatus produces vesicles
Cell plate – newly formed plasma membrane
New membrane releases molecules that form new plant cell walls
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daughter cells
cell plate formation
daughter nucleus
vesicles containing
membrane components
fusing to form cell plate
nucleoli
daughter
nucleus
Figure 8.8 Cytokinesis in
plant cells
© B.A. Palevitz and E.H. Newcomb/BPS/Tom Stack & Associates

25. 8.4 The Cell Cycle Control System
Cell cycle must be controlled
Ensures stages occur in order and only when the previous stage is successfully completed
Cell cycle checkpoints
3 of the many
G1 checkpoint
G2 checkpoint
Mitotic stage checkpoint

26. Mitotic stage checkpoint
G1 checkpoint
Cell committed to divide after this point
Can enter Go if checkpoint not passed
Proper growth signals must be present to pass
DNA integrity checked – if repair not possible, apoptosis occurs
G2 checkpoint
Verifies DNA replicated
DNA damage repaired
Mitotic stage checkpoint
Between metaphase and anaphase
All chromosomes must be attached to the spindle to pass

27. G0 G1 G2 Figure 8.9 Cell cycle checkpoints G1 check point
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G1 check point
Apoptosis can occur
if DNA is damaged
beyond repair G0 G1
M check point
Mitosis stops until
chromosomes
are properly
aligned. M
Control
system
G2 chec kpoint
Mitosis will not
occur until DNA
has replicated. G2 S

28. Internal and external signals
Signal – a molecule that stimulates or inhibits an event
External signals come from outside the cell
Internal signals come from inside the cell
Kinases removes a phosphate from ATP and add it to other molecules
S-cyclin must combine with S-kinase for S phase to occur – DNA replication
M-cyclin must combine with M-kinase for mitosis to occur
Cyclins are present only during certain stages of the cell cycle
Destruction of cyclin at the appropriate time is necessary for normal cell cycle progression

29. Figure 8.10 Internal signals of the cell cycle
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S-kinase
S-cyclin
S-cyclin must combine with S-kinase for the cell cycle to begin DNA replication.
M-cyclin must combine with M-kinase for the cell cycle to start mitosis. G1 M
Control
system G2 S
M-kinase
M-cyclin

30. Cell cycle signals External signals
Epidermal growth factor (EGF) stimulates kin near an injury to finish cell cycle and repair injury
Hormone estrogen stimulates lining of the uterus to divide and prepare for egg implantation
Contact inhibition – cells stop dividing when they touch.
Cells divide about 70 times in culture and then die
Due to shortening of telomeres
Telomere- repeating DNA sequence at end of chromosome

31. Apoptosis Programmed cell death
Remaining cell fragments engulfed by white blood cells
Unleashed by internal or external signals
Helps keep number of cells at appropriate level
Normal part of growth and development
Tadpole tail
Webbing between human digits

32. Figure 8.11 Apoptosis normal cells Cell rounds up, and
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normal cells
Cell rounds up, and
nucleus collapses.
Chromatin condenses,
and DNA fragments. DN A

33. Figure 8.11 Apoptosis continued
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blebs
Plasma membrane
blisters, blebs form.
Cell fragments.
cell fragment DN A
fragment
apoptotic cell
(blebs): Courtesy Klaus Hahn, Cecelia Subauste, and Gary Bikoch from Science Vol. 280, April 3, 1998 p. 32; (apoptotic cell): Courtesy Douglas R. Green, LaJolla Institute for Allergy and Immunology, San Diego

34. 8.5 Cell Cycle and Cancer
Cell cycle regulated by signals that inhibit or promote cell cycle
Cancer may result from imbalance
Cancer is a disease of the cell cycle in which cellular reproduction occurs repeatedly without end.
Classified by location
Carcinoma – cancer of epithelial tissue lining organs
Sarcoma – cancer arising in muscle or connective tissue
Leukemia – cancers of the blood

35. Characteristics of cancer cells
Carcinogenesis – development of cancer
Cancer cells…
Lack differentiation – do not contribute to body function
May be immortal – divide repeatedly
Have abnormal nuclei with abnormal number of chromosomes

36. Cancer cells… Do not undergo apoptosis
Form tumors – do not respond to inhibitory signals
Undergo metastasis (cells travel to start new tumors) and angiogenesis (form new blood vessels to nourish themselves)
Benign – contained within a capsule
Malignant – invasive and may spread

37. Figure 8.12 Development of breast cancer
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path of cancer cells
blood
vessel
benign
tumor
malignant
tumor
lymph
vessel
glands
metastatic
tumor
A single cancer cell grows into
a tumor.
The tumor becomes malignant
and invades nearby tissue.
Cancer cells travel (dotted arrows)
through lymphatic (green) and
blood (red) vessels, and metastatic
tumors form.
a. Development of breast cancer and metastatic tumors

38. Figure 8.12 Development of breast cancer continued
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b. Mammogram showing tumor
© Breast Scanning Unit, Kings College Hospital, London/SPL/Photo Researchers, Inc. 38

39. © Nancy Kedersha/Immunogen/SPL/Photo Researchers, Inc.
Figure 8.13 Cancer cells
Cancer treatment
Either remove tumor or interfere with ability of cancer cells to reproduce
As rapidly dividing cells, they are susceptible to radiation therapy and chemotherapy
Damages DNA or some aspect of mitosis
Leads to side effects
Hormone therapy designed to prevent cells from receiving signals for continued growth and division
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cancer
cells
normal
cells
© Nancy Kedersha/Immunogen/SPL/Photo Researchers, Inc.
750

40. Prevention of cancer Protective behaviors Protective diet
Avoid smoking – accounts for about 30% of all cancer deaths
Avoid sun exposure – major factor in development of most dangerous type of skin cancer, melanomas
Heavy drinkers prone to particular cancers
Protective diet
Weight loss can reduce cancer risk
Increase consumption of foods rich in vitamins A and C
Avoid salt-cured or pickled foods
Include cabbage family members in the diet

41. Figure 8.14 The right diet helps prevent cancer
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(chard): © Roy Morsch/Corbis; (cabbage, berries, broccoli, oranges): © Corbis RF