HLST 126 Chapter 2A Cellular Division PDF

CELLULAR DIVISION MITOSIS AND MEIOSIS COPYRIGHT 2009, JOHN WILEY AND SONS, INC.  Somatic Cell Division - Mitosis  The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two  Human somatic cells contain 23 pairs of chromosomes (tot...

CELLULAR DIVISION MITOSIS AND MEIOSIS COPYRIGHT 2009, JOHN WILEY AND SONS, INC.  Somatic Cell Division - Mitosis  The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two  Human somatic cells contain 23 pairs of chromosomes (total = 46)  The two chromosomes that make up each pair are called homologous chromosomes (homologs)  Somatic cells contain two sets of chromosomes and are called diploid cells  Cell Division  Interphase - the cell is not dividing - the cell replicates its DNA - consists of three phases, G1, S, and G2, replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells  The Cell Cycle Cytosolic Components - main components of the cytoplasm Cell metabolism - refers to all of the chemical reactions that take place inside a cell Centrosome - Contains 2 centrioles  Nuclear Division: Mitosis  Prophase - the chromatin fibers change into chromosomes  Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate  Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell; the chromatids are now called chromosomes  Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form  Cytoplasmic Division: Cytokinesis  Division of a cell’s cytoplasm to form two identical cells  Usually begins in late anaphase  The plasma membrane constricts at its middle forming a cleavage furrow  The cell eventually splits into two daughter cells  Interphase begins when cytokinesis is complete  1 Centrosome: Centrioles Pericentriolar material Nucleolus Nuclear envelope Chromatin Plasma membrane 6 LM all at 700x Cytosol (a) INTERPHASE 2 Kinetochore Centromere Mitotic spindle Chromosome (microtubules) (two chromatids (f) IDENTICAL CELLS IN INTERPHASE Fragments of joined at 5 centromere nuclear envelope Early (b) PROPHASE Late Metaphase plate 3 Cleavage furrow (c) METAPHASE 4 (e) TELOPHASE Cleavage furrow Chromosome Early Late (d) ANAPHASE  Reproductive Cell Division  During sexual reproduction each new organism is the result of the union of two gametes (fertilization), one from each parent  Meiosis - reproductive cell division that occurs in the gonads (ovaries and testes) that produces gametes with half the number of chromosomes  Haploid cells - gametes contain a single set of 23 chromosomes  Fertilization restores the diploid number of chromosomes (46)  Reproductive Cell Division  Meiosis occurs in two successive stages: meiosis I and meiosis II  Each of these two stages has 4 phases: prophase, metaphase, anaphase, and telophase  Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of replicated chromosomes; in Meiosis II, each of the two haploid cells divides, the net result is four haploid gametes that are genetically different from the original diploid starting cell