Cell Cycle and Mitosis

Focus Questions Identify the stages of mitosis and explain what is happening in each step Why is cell division necessary for cells?

Cell Division Cell division is when one cell splits or divides into 2 (or more) new cells.

Purposes of cell division Reproduction in single-celled organisms (asexual reproduction) Growth in multi-cellular organisms Wound repair Distributes identical sets of chromosomes to new cells

DNA DNA is stored in long strands called Chromosomes Chromosomes are made up of DNA

Chromosomes When two identical chromatids are joined together, they are called sister chromatids. Sister chromatids stick together at a special part of the chromosome called the centromere

The Cell Cycle The cell cycle is all of the stages in the life of a cell; the life cycle of a cell. The cell cycle is divided into two major phases: Interphase and Cell Division or M Phase Interphase: The cell is preparing to divide G1 = the cell grows (growth phase) S phase = the DNA is replicated or copied G2 = the cell prepares to divide

The Cell Cycle continued…. Cell Division or M Phase: Mitosis – division of the nucleus and DNA Cytokinesis – division of the cytoplasm of the cell

Mitosis Mitosis is divided into 4 phases Prophase Metaphase Anaphase Telophase PMAT

Prophase Chromosomes condense Centrioles (in animal cells) take position on opposite sides of the nucleus Nuclear envelope disappears Spindle fibers form and attach to chromosomes ** plant cells do not contain centrioles

Metaphase Chromosomes line up down the center of the cell Aster form at the poles of the cell

Anaphase Sister chromatids split Chromatids migrate towards the cell poles

Telophase Final phase of mitosis Nuclear envelopes reform Chromosomes uncoil Cleavage furrow in animal cells Cell plate in plant cells

Cytokinesis Cytoplasm divides equally among the daughter cells

How do cells know when to divide? Signals from the nucleus tell the cell when to divide Age or size of the cell can trigger division Cells stop dividing when they touch other cells = Density Dependent inhibition Cancer is when cells continue to divide out of control