Chapter 10 Sections 1-2: Cell Division

Objectives Name the main events of the cell cycle. Describe what happens during the four phases of mitosis.

Cell Division Cell Division in Eukaryotes is broken into 2 main parts: –Mitosis –Cytokinesis

Reproduction of cells by mitosis is considered asexual reproduction because the cells produced by mitosis are identical to the parent cell. Mitosis begins shortly after the egg is fertilized, producing vast numbers of cells needed for the embryo to take form.

Chromosomes Eukaryotes: genetic information is carried by chromosomes. Chromosomes are made of DNA and proteins.

Cells of every organism have a specific number of chromosomes. Carrot cells: 18 –Human cells: 46 –Fruit Fly cells: 11

Chromosomes are usually spread throughout the nucleus. Before cell division, chromosomes REPLICATE and condense into pairs of SISTER CHROMATIDS.

Each pair of chromatids is attached at an area called the CENTROMERE. A human body cell entering cell division contains 46 chromosomes, all of which consists of two chromatids.

The Cell Cycle Scientists describe the life of the cell through a process called the CELL CYCLE. The cell cycle has 2 MAIN parts: –Cell Growth: Interphase –Cell Division: Mitosis and Cytokinesis

Cell Cycle: process by which a cell grows, prepares for division, and divides to form two daughter cells, each of which then begins the cycle again.

Events of the Cell Cycle The cell cycle consists of 4 phases: 1.M phase: mitosis and cytokinesis 2.S phase: synthesis 3.G 1 Phase: “Gap 1” (phase of growth and development) 4.G 2 Phase: “Gap 2” (phase of growth and development)

During the normal cell cycle, interphase can be quite long, whereas the process of cell division takes place quickly.

Interphase can be broken into 3 phases: 1. G 1 : cells do most of their growing. Cells increase in size and synthesize new proteins and organelles. G1G1 S G2G2

2. S: the S phase follows G 1. In this phase, chromosomes are replicated and synthesis of DNA molecules takes place. G1G1 S G2G2

3. G 2 : This phase occurs after the S phase is complete. This is the shortest of the 3 phases of interphase. During this phase, many of the organelles and molecules required for cell division are produced. After G 2, cell division takes place. G1G1 S S G2G2

Cell Cycle Diagram Directions 1.Define the Cell Cycle 2.LABEL and COLOR the diagram. 1.G 1 : green 2.S: yellow 3.G 2 : blue 4.Interphase: purple 5.Cell Division & Mitosis: Your choice, but use different colors. 6.Describe (in your own words) what happens in each phase.

Mitosis Biologists divide the events of mitosis into four phases 1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

Prophase First and longest phase Chromosomes become visible Centrioles separate and take up positions on opposite sides of the nucleus. Spindles form, which help to separate chromosomes by attaching to their centromeres.

Plant cells do not have centrioles, but still form spindles. Near the end of prophase, chromosomes coil more tightly. Nucleolus disappears, and the nuclear envelope breaks down.

Metaphase Lasts only a few minutes. Chromosomes line up across the center of the cell. Microtubules connect the centromere of each chromosome to the two poles of the spindle.

Anaphase Centromeres that join the sister chromatids split. Sister chromatids separate, becoming individual chromosomes. Chromosomes move to opposite poles of the spindle.

Telophase Chromosomes begin to disperse into a tangle of dense material. Nuclear envelope reforms around each cluster of chromosomes. Spindle begins to break apart. Nucleolus becomes visible.

Cytokinesis Division of the cytoplasm itself. Usually occurs at the same time as telophase Animal Cells: membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. Plant Cells: cell plate forms and develops into a separating membrane. Cell wall begins to appear in the cell plate.