Mitosis and the Cell Cycle Cell reproduction Biology

Mitosis and the Cell Cycle Cell reproduction

Biology is the only subject in which multiplication is the same thing as division… S 1

Why do cells divide… § One-celled organisms 1. for reproduction amoeba § Multi-celled organisms 1. for growth & development § 2. from fertilized egg to adult for repair & replacement § replace cells that die from normal wear & tear or from injury S 6 starfish

The Cell Cycle---life cycle of a cell n The sequence of growth and division of a cell. n The cell cycle occurs in a series of stages, or phases n 95% of cell cycle is in interphase n 5% of cell cycle is in mitosis and cytokinesis

Stage 1 Interphase n Stage between cell division Most of the cell’s life takes place in Interphase n Chromosome replication (their number doubles)

Interphase continued— the chromosmes become a pair of chromatids and are held together by a centromere Centromere n This stage ends in preparation for mitosis(dividing of the cell )

Stage 2 Mitosis n. Happens in all eukaryotic cells n. Cell division process n 4 major stages or steps n REMEMBER PMAT

Prophase n. Prepare for cell division

n Mitosis begins (cell begins to divide) n 1. Chromatin condenses to form X like structures n 2. Spindle fibers form between the poles n 3. Nuclear membrane breaks down duplicated chromosomes (prophase) cell nucleus S 16

Metaphase n. Meet in the Middle

n Chromosomes line up across the middle of the cell with sister chromatid at equator n Spindle fibers attach to centromere metaphase duplicated chromosomes lined up in middle of cell

Anaphase AWAY– the chromatids are pulled away from each other.

n Centromeres break n Each chromatid is now a separate chromosome n Each chromosome is pulled to each pole of the cell anaphase chromosomes split & move to opposite ends S 18

Telophase Tearing apart into Two cells.

n Cell begins to pull in two n Two new nuclear envelopes form and surround each set of chromosomes n Chromosomes unwind into long strands n Last stage of mitosis telophase S 19

3 rd Stage Cytokinesis n Cell membrane pinches down and divides the cytoplasm n Two new identical daughter cells are formed n In cells that have a cell wall a cell plate forms between the new cells and then becomes the cell wall

Summary Cell Cycle 1. Interphase—growing stage 2. Mitosis—dividing stage 4 Stages a. Prophase—Preparing b. Metaphase—Meeting the Middle c. Anaphase—attachment changes d. Telophase—Tearing into two 3. Final Process Cytokinesis-2 new daughter cells