Biology 101 Module 8

1. 8-1
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3. The Basics of
Cellular
Reproduction
Multicellular organisms
begin life as a single cell.
Humans become trillions
of cells because of cellular
reproduction.
Reproduction continues
as we grow to replace
worn-out or damaged
tissues.

4. Cellular
Reproduction
• All cells come from cells.
• Cellular reproduction is necessary
for the production of both new
cells and new organisms.
• Asexual reproduction
• Doesn’t require sperm or egg
• Single cell makes a clone of itself

5. Cellular
Reproduction
• Growth—cell duplicates its
contents (including DNA and
organelles)
• Cell division—parent cell
contents divides into two
daughter cells
• Both processes are heavily
regulated
Two important processes

6. 8-6
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8. Sister
Chromatids
•

10. 8-10

11. The Cell Cycle

12. Interphase
Majority of the cell cycle
Time when a cell performs its usual functions
Amount of time varies widely depending on cell
Three stages:
• G1- growth and normal cellular functions
• S - DNA synthesis/replication
• G2 - growth and preparation to divide

13. Interphase
Interphase is divided into three 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 being
composed of two sister chromatids
• G2—stage following DNA synthesis
• Extends to onset of mitosis
• Synthesizes proteins needed for cell
division

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16. Daughter
Nuclei
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.
Daughter nuclei produced by mitosis are
genetically identical to each other and to
the parent nucleus.

17. Spindle
Fibers Are
Part of the
Cytoskeleton
Mitotic Spindle:
• Most eukaryotic cells rely on this
structure to pull chromatids apart.
• Part of the 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.

18. Mitosis Is a
Continual
Process
Traditionally divided into four phases:
• Prophase—chromosomes are visible
under microscope in condensed pairs
• Metaphase—chromosomes line up
along equatorial plate (middle)
• Anaphase—chromosomes are pulled to
opposite poles of cell (apart)
• Telophase and Cytokinesis—two
distinct cells are visible under the
microscopes

19. 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 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.
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.
Cell cycle 𝐆 𝟏, S, 𝐆 𝟐 Cell cycle M: Phases of mitosis

20. Metaphase
During metaphase, the
chromosomes are aligned at the
spindle equator midway 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.
Telophase and Cytokinesis
During telophase, the spindle disappearsas 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.
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
Phases of mitosis

21. Phases
of
Mitosis
in
Animal
Cells
Although mitosis is divided into phases, it
is a continuous process.
DNA is replicated before mitosis begins.
Each chromosome consists of two 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

22. Mitosis
Differs in
Plants and
Animals
Plant and animal cells differ.
• Plant—have centrosomes but
lack centrioles
• Animal—each centrosome has
two centrioles and an aster
(array of microtubules)

23. Nucleolus has disappeared, and
duplicatedchromosomes are visible.
Centrosomes begin moving apart, and
spindle is in process of forming.
The kinetochoreof each chromatidis
attachedto a kinetochore spindle fiber.
Polar spindle fibers stretch from each
spindle pole and overlap.
Metaphase
Centromeres of duplicatedchromosomes are
aligned at the metaphase plate (center of fully
formed spindle). Kinetochore spindle fibers
attachedto the sister chromatids come from
opposite spindle poles.

24. (anaphase, telophase): © Kent Wood /Science Source
Telophase
Daughter cells are forming as
nuclear envelopes and nucleoli
reappear. Chromosomes will
become indistinct chromatin.
Anaphase
Sister chromatids part and become daughter
chromosomes that move toward the spindle
poles. In this way, each pole receives the same
number and kinds of chromosomes as the
parent cell.

25. Cytokinesis
Cytokinesis in animal and plant cells
• Accompanies mitosis in most but not all
cells
• Mitosis without cytokinesis results in a
multinucleated cell
• Muscle cells in vertebrate animals
• Embryo sac in flowering plants

27. 8-27
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29. 8-29
The Cell
Cycle
Control
System
• Cell cycle must be controlled
• Ensures that the stages occur in order and
that the cycle continues only when the
previous stage is successfully completed
• Cell cycle checkpoints
• Three of the many
• G1 checkpoint
• G2 checkpoint
• Mitotic stage checkpoint

30. Three of the
Many
Checkpoints
G1 checkpoint:
• Cell committed to divide after this point
• Can enter G0 if checkpoint not passed
• Proper growth signals must be present to pass
• DNA integrity checked—if repair is not possible,
apoptosis occurs
G2 checkpoint:
• Verifies that DNA replicated
• DNA damage repaired
Mitotic stage checkpoint:
• Between metaphase and anaphase
• All chromosomes must be attached to spindle to
pass.

31. Cell Cycle Checkpoints

32. 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 remove a phosphate from ATP and
add it to other molecules.
Cyclins are internal signals present only
during certain stages of the cell cycle.
Destruction of cyclin at the appropriate time
is necessary for normal cell cycle progression.

33. Cell Cycle
Signals
External signals
• Epidermal growth factor (EGF) stimulates
skin 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

34. 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

37. Cell Cycle
and Cancer
• Cell cycle is 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.

38. Development
of Cancer
Cell (red) acquires a
mutation for repeated
cell division.
New mutations arise,
and one cell (teal) has
the ability to start a
tumor.
New metastatic tumors
are found some distance
from the original tumor.
Cells have gained the
ability to invade
underlying tissues by
producing a proteinase
enzyme.
Cancer cells now
have the ability to
invade lymphatic and
blood vessels.
Cancer in situ.The
tumor is at its place of
origin. One cell (purple)
mutates further.

39. Proto-
oncogenes and
Tumor
Suppressor
Genes
• Proto-oncogenes code for proteins that
promote the cell cycle and inhibit apoptosis.
They are often likened to the gas pedal of a
car because they accelerate the cell cycle.
• Tumor suppressor genes code for proteins
that inhibit the cell cycle and promote
apoptosis.
• When proto-oncogenes mutate, they
become cancer-causing genes called
oncogenes.
• When tumor suppressor genes mutate, their
products no longer inhibit the cell cycle or
promote apoptosis.

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43. Characteristics
of Cancer
• 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

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45. Cancer cells travel
(dotted arrow)
through lymphatic
(green) and blood
(red) vessels, and
metastatic tumors
form.
A single cancer cell
grows into a tumor.
The tumor becomes
malignant and
invades nearby tissue.

46. Cancer
Treatment
• Either remove tumor or interfere with the
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 is designed to prevent
cells from receiving signals for continued
growth and division.

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48. Chapter 8 Objective Summary
• You should now be able to:
• 1. Summarize the purpose of cellular reproduction.
• 2. Explain the relationship between levels of DNA structure including
chromatin, chromosomes (histones), and sister chromatids
(centromeres).
• 3. Summarize the activities that occur in the cell during interphase.
• 4. Summarize the events in each phase of mitosis (prophase,
metaphase, anaphase, telophase).
• 5. Compare and contrast cytokinesis in a plant versus animal cell.
• 6. Explain the role of checkpoints in the cell cycle and how they are
regulated.
• 7. Describe how proto-oncogenes and tumor suppressor genes control
the cell cycle and can lead to cancer.
• 8. Describe the characteristics of cancer cells.