Nematoda Secernenta in Anaphase Contributed by Richard J. Harris courtesy of BIODIDAC

1. Mitosis- division of the cell nucleus 2. Cytokinesis- division of the cytoplasm

SEM image of Chromosomes

1. Chromosomes- contain DNA (genetic info) which is passed from parent to offspring. 2. Before a cell divides each chromosome is copied

3. Structure of the chromosome: * Two sister chromatids; are identical * Centromere- holds the sister chromatids together resulting in an x-shaped c’some Sister chromatids Centromere

* When the cell divides, the chromatids separate. * Each new cell gets one chromatid. Cell division Micrograph

1. Cell Cycle- the series of events that takes place in a cell leading to its division & replication 2. During the cell cycle: * a cell grows * prepares for division 3. Divides to form two daughter cells, each of which begins the cycle again

4. The cell cycle consists of four phases: * G1 (First Gap Phase) * S Phase (Synthesis) * G2 (Second Gap Phase) * M Phase (Mitosis)

1. Interphase- the first stage of the cell cycle. During this phase the cell: * Grows * Makes new proteins & organelles * C’somes are replicated * DNA is made 2. Interphase has 3 phases: G1, S, & G2

3. During G1, the cell: * increases in size * synthesizes new proteins and organelles 4. During the S phase: * chromosomes are replicated * DNA synthesis takes place 5. Once a cell enters the S phase, it usually completes the rest of the cell cycle

6. The G2 Phase (Second Gap Phase) * organelles & molecules required for cell division are produced * Once G2 is complete, the cell is ready to start the M phase— Mitosis

1. Mitosis has 4 phases: * Prophase * Metaphase * Anaphase * Telophase

2. Centrioles- barrel shaped structures that are made of groupings of microtubules

3. Spindle- a fanlike microtubule structure that helps separate the chromosomes.

4. Chromatin- a combination of DNA and proteins that make up c’somes

5. Prophase * The 1 st & longest phase of mitosis * The centrioles separate & end up on opposite sides of the nucleus in an area called the centromere * Chromatin condenses into chromosomes. * The nuclear envelope breaks down. A cell in prophase of mitosis. (An epithelial cell in prophase of mitosis, treated with the anti-cancer drug taxol. Chromosomes are labeled blue. Taricha granulosa (newt) lung.) Observing Mitosis with Fluorescence Microscopy. Prophase. © by Michael W. Davidson and The Florida State University.

6. Metaphase * 2 nd phase of mitosis * The chromosomes line up across the center of the cell * Microtubules connect the centromere of each chromosome to the poles of the spindle. Observing Mitosis with Fluorescence Microscopy. Metaphase. © by Michael W. Davidson and The Florida State University.

7. Anaphase * 3 rd phase of mitosis * the duplicated centromeres of each pair of sister chromatids separate * the now-daughter chromosomes begin moving toward opposite poles until they have separated into two groups. Observing Mitosis with Fluorescence Microscopy. Anaphase. © by Michael W. Davidson and The Florida State University

8. Telophase * The last phase of mitosis * Chromosomes gather at opposite ends of the cell * A new nuclear envelope forms around each bunch of chromosomes. Observing Mitosis with Fluorescence Microscopy. Telophase. © by Michael W. Davidson and The Florida State University.

9. Cytokinesis * the cytoplasm pinches in half. * Each daughter cell has an identical set of duplicate chromosomes. Actin (blue) and microtubules (orange) at the end of cytokinesis in a green urchin zygote. University of Washington Center for Cell Dynamics

* structure known as the cell plate forms midway between the divided nuclei * The cell plate gradually develops into a separating membrane. * A cell wall then begins to appear in the cell plate. Cell wallCell plate

* A cleavage furrow forms-An indention formed by microfilaments * The pulling of the filaments separates the cytoplasm of the daughter cells

* 95% of the cell cycle is spent in interphase * A typical rapidly dividing human cell with a total cycle time of 24 hours: * the G1 phase might last about 11 hours * S phase about 8 hours * G2 about 4 hours * and M about 1 hour.

* Page 249 “Analyzing Data- The Life Span of Human Cells” * Read the paragraph and answer questions 1-4