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Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 11
How Cells Reproduce
(Sections 11.4 - 11.6)
Albia Dugger • Miami Dade College
11.4 Cytokinesis: Division of Cytoplasm
• A cell’s cytoplasm divides after mitosis to form two cells
• The process of cytoplasmic division (cytokinesis) is different
in plants and animals
• cytokinesis
• Cytoplasmic division
Cytoplasmic Division of Animal Cells
• A contractile ring of actin and myosin filaments forms around
the cell’s midsection and contracts, forming a cleavage
furrow (like a belt) around the cell which pinches the cell in
two
• cleavage furrow
• In a dividing animal cell, the indentation where cytoplasmic
division will occur
Cytoplasmic Division of Animal Cells
• The spindle begins to
disassemble
• A ring of filaments
attached to the plasma
membrane contracts
Cytoplasmic Division
of Animal Cells (cont.)
• A cleavage furrow
• Cell is pinched in two
Cytoplasmic Division of Animal Cells
Fig. 11.6, p. 168
Cytoplasmic Division of Animal Cells
After mitosis is
completed, the spindle
begins to disassemble.
1
Fig. 11.6.1, p. 168
Cytoplasmic Division of Animal Cells
At the midpoint of the
former spindle, a ring of
actin and myosin filaments
attached to the plasma
membrane contracts.
2
Fig. 11.6.2, p. 168
Cytoplasmic Division of Animal Cells
This contractile ring
pulls the cell surface
inward as it shrinks.
3
Fig. 11.6.3, p. 168
Cytoplasmic Division of Animal Cells
The ring contracts
until it pinches the
cell in two.
4
Fig. 11.6.4, p. 168
Cytoplasmic
Division of
Animal Cells
1 After mitosis is
completed, the spindle
begins to disassemble.
2 At the midpoint of the
former spindle, a ring of
actin and myosin filaments
attached to the plasma
membrane contracts.
3 This contractile ring
pulls the cell surface
inward as it shrinks.
4 The ring contracts
until it pinches the cell
in two.
Stepped Art
Fig. 11.6, p. 168
Cytoplasmic Division of Plant Cells
• Plant cell cytoplasmic division is different because plants have
stiff cell walls outside their plasma membranes
• Microtubules guide vesicles from Golgi bodies and the cell
surface to the plane of division, where they form a cell plate
• cell plate
• Disk-shaped structure that forms a cross-wall between
two new plant-cell nuclei
• Develops into a primary cell wall that merges with the
parent cell’s wall
Cytoplasmic Division of Plant Cells
• Vesicles cluster at the future
plane of division when
mitosis ends
• Vesicles form a cell plate
along the plane of division
Cytoplasmic Division of Plant Cells
• Cell plate expands and
partitions the cytoplasm
• Cell plate matures as two
new cell walls
Cytoplasmic
Division of Plant
Cells
Fig. 11.7, p. 168
Cytoplasmic Division of Plant Cells
The future plane of division
was established before mitosis
began. Vesicles cluster here
when mitosis ends.
5
Fig. 11.7.5, p. 168
Cytoplasmic Division of Plant Cells
As the vesicles fuse with
each other, they form a cell
plate along the plane of
division.
6
Fig. 11.7.6, p. 168
Cytoplasmic Division of Plant Cells
The cell plate expands
outward along the plane of
division. When it reaches the
plasma membrane, it attaches
to the membrane and partitions
the cytoplasm.
7
Fig. 11.7.7, p. 168
Cytoplasmic Division of Plant Cells
The cell plate matures as two
new cell walls. These walls join
with the parent cell wall, so
each descendant cell becomes
enclosed by its own cell wall.
8
Fig. 11.7.8, p. 168
Cytoplasmic
Division of
Plant Cells
5 The future plane of division
was established before mitosis began.
Vesicles cluster here when mitosis ends.
6 As the vesicles fuse with each other,
they form a cell plate along the plane of
division.
7 The cell plate expands outward along
the plane of division. When it reaches the
plasma membrane, it attaches to the
membrane and partitions
the cytoplasm.
8
The cell plate matures as two new cell
walls. These walls join with the parent cell
wall, so each descendant cell becomes
enclosed by its own cell wall.
Stepped Art
Fig. 11.7, p. 168
Key Concepts
• Cytoplasmic Division
• After nuclear division, the cytoplasm divides
• Typically, one nucleus ends up in each of two new cells
• The cytoplasm of an animal cell simply pinches in two
• In plant cells, a cross-wall forms in the cytoplasm and
divides it
11.5 Controls Over Cell Division
• The cell cycle has built-in checkpoint genes that allow
problems to be corrected before the cycle advances
• Products of “checkpoint” genes monitor whether a cell’s DNA
has been copied completely, or if it is damaged
• If the problem remains uncorrected, checkpoint gene products
cause the cell to
self-destruct
When Checkpoints Fail
• On rare occasions, controls over cell division are lost, and
division occurs over and over with no resting period
• The cell’s descendants form a neoplasm, an accumulation of
cells that lost control over how they grow and divide
• neoplasm
• An accumulation of abnormally dividing cells
Growth Factors
• Cells of most neoplasms carry mutations resulting in
overabundance of epidermal growth factor (EGF), which
stimulates a cell to enter mitosis
• growth factor
• Molecule that stimulates mitosis
11.6 Cancer: When Control Is Lost
• Mutations that alter products of checkpoint genes are
associated with an increased risk of tumor formation
• Once a tumor-causing mutation has occurred, the mutated
gene is called an oncogene
• Checkpoint genes encoding proteins that promote mitosis are
called proto-oncogenes because mutations can turn them
into oncogenes
Key Terms
• tumor
• A neoplasm that forms a lump
• oncogene
• Gene that has the potential to transform a normal cell into
a tumor cell
• proto-oncogene
• Gene that can become an oncogene
Tumor Suppressors
• Checkpoint gene products that inhibit mitosis are called
tumor suppressors because tumors form when they are
missing
• Example: Products of BRCA1 and BRCA2 genes regulate
expression of DNA repair enzymes
Benign and Malignant Neoplasms
• Benign neoplasms are not dangerous
• Example: Ordinary skin moles
• A malignant neoplasm is one that gets progressively worse,
and is dangerous to health
• Cancer occurs when abnormally dividing cells of a malignant
neoplasm disrupt body tissues physically and metabolically
Characteristics of Malignant Cells
1. Malignant cells grow and divide abnormally.
• Populations may reach extremely high densities with cell
division occurring very rapidly
2. Cytoplasm and plasma membrane are altered
• The balance of metabolism is often shifted
• Altered or missing proteins impair membrane function
3. Metastasis: The process in which malignant cells migrate
and establish neoplasms elsewhere in the body
Benign and Malignant Neoplasms
Benign and
Malignant
Neoplasms
1 malignant neoplasm
2 malignant neoplasm
3
4
Fig. 11.10, p. 170
Benign and Malignant Neoplasms
1 malignant neoplasm
Fig. 11.10.1, p. 170
Benign and Malignant Neoplasms
2 malignant neoplasm
Fig. 11.10.2, p. 170
Benign and
Malignant
Neoplasms
3
4
Fig. 11.10.3,4, p. 170
Three Types of Skin Cancers
• Basal cell carcinoma is
the most common type
of skin cancer
• This slow-growing,
raised lump may be
uncolored, reddishbrown, or black
Three Types of Skin Cancers
• Squamous cell
carcinoma is the second
most common form of
skin cancer
• This pink growth, firm to
the touch, grows under
the surface of skin
Three Types of Skin Cancers
• Melanoma spreads
fastest
• Cells form dark,
encrusted lumps that
may itch or bleed easily
Treating Cancer
• Cancer causes 15 to 20 percent of all human deaths –
neoplasms that are detected early can often be removed by
chemotherapy or surgery before metastasis occurs
• Life-style choices such as not smoking and avoiding exposure
of unprotected skin to sunlight can reduce one’s risk of
acquiring mutations that cause cancer
Key Concepts
• The Cell Cycle Gone Awry
• Built-in mechanisms monitor and control the timing and
rate of cell division
• On rare occasions, the surveillance mechanisms fail, and
cell division becomes uncontrollable
• Tumor formation and cancer are outcomes