Albia Dugger Miami Dade College Chapter 11 How Cells Reproduce

HeLa Cells

11.2 Multiplication by Division Nuclear division followed by cytoplasmic division Called the cell cycle

The Life of a Cell Cell cycle A sequence of three stages (interphase, mitosis, and cytoplasmic division)

Interphase G1: Interval of cell growth and activity S: Interval of DNA replication (synthesis) G2: Interval when the cell prepares for division

Interphase and the Life of a Cell Most cell activities take place during G1 Control mechanisms work at certain points in the cell cycle; some can keep cells in G1 Loss of control may cause cell death or cancer

Mitosis and Asexual Reproduction Mitosis is a nuclear division mechanism that maintains the chromosome number Growth Repair Asexual reproduction, a single individual can reproduce by mitosis and cytoplasmic division

Cell Division in Frog Embryos

Homologous Chromosomes Homologous chromosomes are pairs of chromosomes having the same length, shape, and genes Human cells have 46 chromosomes (23 pairs) Except for a pairing of sex chromosomes (XY) in males, the chromosomes of each pair are homologous

A An unduplicated pair of chromosomes in a cell in G1. Stepped Art B By G2, each chromosome has been duplicated. C Mitosis and cyto- plasmic division package one copy of each chromosome into each of two new cells. Figure 11-4 p179

Figure 11-2 p177 prophase G2 metaphase S mitosis telophase anaphase G1 interphase

Interphase in Plant and Animal Cells Onion root cellWhitefish embryo cell

Mitosis

Prophase Chromosomes condense Microtubules form a bipolar spindle Nuclear envelope breaks up Microtubules attach to the chromosomes

The Spindle Spindle A dynamic network of microtubules that forms during nuclear division

Metaphase and Anaphase Metaphase All duplicated chromosomes line up midway between the spindle poles Anaphase Microtubules separate the sister chromatids of each chromosome and pull them to opposite spindle poles

Telophase Two clusters of chromosomes reach the spindle poles A new nuclear envelope forms around each cluster Two new nuclei are formed, each with the same chromosome number as the parent cell

Mitosis

11.4 Cytokinesis: Division of Cytoplasm Cytokinesis The process of cytoplasmic division

Cytokinesis in Animal and Plant Cells Animal cells A cleavage furrow partitions the cytoplasm Plant cells A cell plate partitions the cytoplasm

Cytoplasmic Division in Animal Cells After mitosis is completed, the spindle begins to disassemble. 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. The ring contracts until it pinches the cell in two

Cytoplasmic Division in Plant Cells The future plane of division was established before mitosis began. Vesicles cluster here when mitosis ends. As the vesicles fuse with each other, they form a cell plate along the plane of division. 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. 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

11.6 When Mitosis Becomes Pathological On rare occasions, controls over cell division are lost and a neoplasm forms Cancer develops as cells of a neoplasm become malignant

Checkpoint Failure and Tumors Neoplasm – a group of cells that lost control over how they grow and divide Tumor (abnormal mass)

Oncogenes and Overactive EGF Receptors

Checkpoint Genes in Action

Cancer Benign neoplasms (such as ordinary skin moles) grow slowly, stay in one place, and are not cancerous Malignant neoplasms (cancers) disrupt body tissues, both physically and metabolically

Three Characteristics of Cancer Cells 1.Cancer cells grow and divide abnormally; capillary blood supply to the cells may increase abnormally 2.Malignant cells typically have an abnormal chromosome number 3.Cancer cells have weakened adhesion – malignant cells break loose and invade other parts of the body (metastasis)

Figure p185 Benign neoplasms grow slowly and stay in their home tissue. Cells of a malignant neoplasm can break away from their home tissue. The malignant cells become attached to the wall of a blood vessel or lymph vessel. They release digestive enzymes that create an opening in the wall, then enter the vessel. The cells creep or tumble along inside blood vessels, then leave the bloodstream the same way they got in. They often start growing in other tissues, a process called metastasis

Reducing the Risk of Cancer Each year, cancer causes 15 to 20 percent of all human deaths in developed countries Life style choices such as not smoking and avoiding exposure of unprotected skin to sunlight can reduce the risk of acquiring mutations that lead to cancer Some neoplasms can be detected with periodic screening procedures such as Pap tests or dermatology exams

Skin Cancers A Basal cell carcinoma is the most common type of skin cancer. This slow- growing, raised lump may be uncolored, reddish- brown, or black. B The second most common form of skin cancer is a squamous cell carcinoma. This pink growth, firm to the touch, grows under the surface of skin.