CELL REPRODUCTION Kimberly Lozano Biology 490 Spring 2010 CELL CYCLE Interphase G1: Growth (1) New organelles form within the cell. S: Synthesis Cell duplicates its DNA. G2: Growth (2) Cell prepares for division to take place during the mitotic phase. Mitotic M phase Mitosis. Chromosomes divide. Cytokinesis. Cytoplasm and cell membrane divide. Chromosomes as Packaged Genes DNA double helix bound to histones DNA wrapped around histones form nucleosome Further coiling of nucleosome produce 30nm wide chromatin fiber Coiling of chromatin fiber produce x shaped chromosome Chromosome consists of two identical sister chromatids joined at the centromere 1
Prokaryotic Chromosome Single circular chromosome Plasmids What is Mitosis? Mitosis produces two daughter cells that are identical to the parent cell. If the parent cell is haploid (N), then the daughter cells will be haploid. If the parent cell is diploid, the daughter cells will also be diploid. N N 2N 2N This type of cell division allows multicellular organisms to grow and repair damaged tissue. centrioles Interphase Chromatin is condensing into chromosomes and centrioles have duplicated in preparation for mitosis. Chromosomes are not visible because they are uncoiled Chromatin nuclear envelope Prophase Duplicated chromosomes are visible. Centrioles begin moving apart. Nuclear envelope is fragmenting and will disappear. 2
Metaphase The spindle fully develops and the chromosomes align at the metaphase plate Anaphase Chromosomes are pulled along the microtubules toward opposite poles of the cell Telophase The cell divides into two. The chromosomes uncoil. The nucleus reforms. The spindle apparatus disassembles. Cytokinesis Not a phase of mitosis. Division of cytoplasm. Begins as the cell lengthens in anaphase and ends with separation of daughter cells being complete at end of telophase. What is Meiosis? Meiosis produces daughter cells that have one half the number of chromosomes as the parent cell. 2N N Meiosis enables organisms to reproduce sexually. Gametes (sperm and eggs) are haploid. Meiosis involves two divisions producing a total of four daughter cells. 3
Prophase I Early Homologous pairs within cell become visible. Replication of genetic material has already occurred. Middle Homologous chromosomes synapse, become shorter, thicker. Late Chromosomes become double stranded.. Crossing-over and Recombination During Meiosis Variation Survival of organism Crossing over Metaphase I Homologous pairs become aligned in the center of the cell. 4
Anaphase I Centromeres on the chromosomes do not divide. Double stranded chromosomes move apart to opposite poles. Telophase I This stage is absent in some species. Two haploid cell start to form (Half the number). Interkinesis Interkinesis is similar to interphase except DNA synthesis does not occur. Chromosomes have faded from view. Prophase II Nuclear envelope breaks down and spindle apparatus appears. Metaphase II Chromosomes become arranged on the metaphase plate and are attached to the now fully formed spindle. Anaphase II Centromeres separate and two chromatids of each chromosome move to opposite poles on the spindle. Separated chromatids are now called chromosomes. Telophase II A nuclear envelope forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells, each with a haploid set of chromosomes 5
Meiosis results Chromosomes fade from view. Total of four haploid cells are produced. Next phase would be fertilization. Daughter Cells Sexual Reproduction and Genetic Variability Enhances potential for survival of species Genetic variability by recombination of whole chromosomes Cited Literature Fried, George and Hademos, George Schaum s Outline of Biology. New York: McGraw Hill, 2009. Sadava, David, C. Heller, G. Orians, W. Purves, D. Hillis, Life. The Science of Biology, Eighth Edition,Volume 1, The Cell and Heredity. Virginia: W.H.Freeman, 2006. 6