Albia Dugger Miami Dade College Cecie Starr Christine Evers Lisa Starr Chapter 11 How Cells Reproduce (Sections )

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 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 furrowCell is pinched in two

Fig. 11.6, p. 168 Cytoplasmic Division of Animal Cells

Fig , p. 168 After mitosis is completed, the spindle begins to disassemble. 1 Cytoplasmic Division of Animal Cells

Fig , p At the midpoint of the former spindle, a ring of actin and myosin filaments attached to the plasma membrane contracts. Cytoplasmic Division of Animal Cells

Fig , p. 168 This contractile ring pulls the cell surface inward as it shrinks. 3 Cytoplasmic Division of Animal Cells

Fig , p The ring contracts until it pinches the cell in two. Cytoplasmic Division of Animal Cells

Fig. 11.6, p. 168 Stepped Art After mitosis is completed, the spindle begins to disassemble. 1 2 At the midpoint of the former spindle, a ring of actin and myosin filaments attached to the plasma membrane contracts. This contractile ring pulls the cell surface inward as it shrinks. 3 4 The ring contracts until it pinches the cell in two. Cytoplasmic Division of Animal Cells

ANIMATION: Cytoplasmic division To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

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

Fig. 11.7, p. 168 Cytoplasmic Division of Plant Cells

Fig , p. 168 The future plane of division was established before mitosis began. Vesicles cluster here when mitosis ends. 5 Cytoplasmic Division of Plant Cells

Fig , p. 168 As the vesicles fuse with each other, they form a cell plate along the plane of division. 6 Cytoplasmic Division of Plant Cells

Fig , p. 168 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 Cytoplasmic Division of Plant Cells

Fig , p. 168 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 Cytoplasmic Division of Plant Cells

Fig. 11.7, p. 168 Stepped Art The future plane of division was established before mitosis began. Vesicles cluster here when mitosis ends. 5 As the vesicles fuse with each other, they form a cell plate along the plane of division. 6 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 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 Cytoplasmic Division of Plant Cells

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 checkpoints 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

Checkpoint Genes in Action Radiation damaged DNA in this nucleus – dots show products of checkpoint genes that recruit DNA repair enzymes

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

A Neoplasm Stained cells of this neoplasm have an abnormal overabundance of phosphorylated EGF receptor Mitosis is being continually stimulated

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

Fig , p. 170 malignant neoplasm Benign and Malignant Neoplasms

Fig , p. 170 malignant neoplasm 1 Benign and Malignant Neoplasms

Fig , p malignant neoplasm Benign and Malignant Neoplasms

Fig ,4, p Benign and Malignant Neoplasms

ANIMATION: Cancer and metastasis To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

Three Types of Skin Cancers Basal cell carcinoma is the most common type of skin cancer This slow-growing, raised lump may be uncolored, reddish- brown, 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

ANIMATION: The cell cycle and cancer - Phases To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

ANIMATION: The cell cycle and cancer - Growth factor control To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERECLICK HERE

Henrietta’s Immortal Cells (revisited) Overexpression of Aurora B protein (green) in cancer cells correlates with shortened patient survival rates Drugs that inhibit Aurora B are being tested as potential cancer therapies

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