Cell Division Continuity of Life

Common Features of all types of cell division DNA replication must occur prior to cell division DNA must be distributed to daughter cells Daughter cells contain equivalent quantities of DNA

Types of cell division Binary fission Mitosis Meiosis Occurs in Prokaryotic organisms Purpose- growth in numbers Mitosis Occurs in most eukaryotic cells Maintains chromosome number Meiosis Occurs in germ cells Purpose- produce haploid cells

Binary Fission Simple process Single chromosome Duplication of DNA Invagination of plasma membrane Formation of daughter cells Time frame- 15 minutes to several hours Video

Mitosis Form of nuclear division Complex process Several linear chromosomes involved Chromosome number maintained 4 major steps required Steps result in appropriate distribution of chromosomes Mechanism of growth for most eukaryotic cells Carried out in somatic cells

Steps in Mitosis Interphase Prophase Metaphase Anaphase Telophase (Cytokinesis)

Prophase Chromosomes condense Centrosome (may contain centriole) duplicates Nuclear envelope breaks up Spindle fiber forms from microtubules Chromosomes hooked onto spindle fibers

Chromosome Structure

Condensed DNA

Metaphase Spindle fibers pull chromatids in opposite directions Chromosomes align at the cell equator Concludes when chromatids separate

Anaphase Chromatids now unduplicated chromosomes Chromosomes move to opposite poles of the cell Concludes when chromosomes reach opposite poles

Telophase Chromosomes decondense Nuclear envelope reforms Cytokinesis usually begins

Cytokinesis Cytoplasmic division Animal cells form furrow by contracting microfilaments at the equator See text page 133 Plant cells form a cell plate by depositing vesicles containing cellulose at the equator video

Cell cycle Interphase G1- Cell growth S- DNA replication G2- Preparation for mitosis M- Mitosis G0- waiting mode video

Meiosis Form of nuclear division Reduces the chromosome number by ½ Two stages Meiosis I Meiosis II Crossing over between homologues Occurrs in all sexually reproducing organisms Produces gametes in most organisms Haploid cells Provides genetic diversity Stages similar to mitosis http://www.youtube.com/watch?v=D1_-mQS_FZ0

Cancer Loss of cell growth control No G0 Check points transgressed