Genetics and Cellular Function replication and the cell cycle Mitosis Mitosis? Mitosis: division of cells that results in daughter cells with the same the genetic information that the original cell had. 4- Diploid n Diploid n 7- and Cell Cycle before cell divides, it must must duplicate its (replication) - so each new cell gets exact copy of Recall Law of Complementary Base Pairing 4- -5 When cells divide, replicates itself and identical copies go to daughter cells Helicases break hydrogen bonds to produce free s of - Primase: Installs RNA primer polymerase binds to primer and starts adding complementary copies to original Using A-T, C-G pairing rules Thus each copy is composed of new and old (called semiconservative replication) Original sequence is preserved. Primase sets up short sequence of RNA. Polymerase adds complimentary 4. RNA Primer is replaced with. Helicase breaks H bonds 5. ligase joins segments together -5-5
Primase Primase!!!! Installs RNA Primer Incoming Continuous (e) RNA primer template polymerase III Parental (b) Replication polymerase Discontinuous RNA primer Newly made fork polymerase I (a) RNA primer Key helicase being replaced by A T (c) Gap in (d) replication C G ligase Figure 4-7 4.4 Okazaki fragments Completed daughter (a) Key: = Adenine = Thymine = Cytosine = Guanine Replication fork polymerase III Old (template) Newly made Leading New Lagging of one chromatid Old (template) polymerase III Errors and Mutations polymerase does make mistakes But: checks new base pairs and tends to fix mistakes result is only error per billion bases replicated mutations - changes in structure due to replication errors or environmental factors (radiation, viruses, chemicals) some mutations = no problem/some kill the cell, turn it cancerous or cause genetic defects in future generations 4-
Centriole Chromatids Spindle fibers Cleavage furrow Nuclear re- 4 Chromatin Daughter cells in interphase 9/5/0 Cell Cycle Most cells of body are in interphase - the non-dividing stage of life cycle Interphase is subdivided into: G - cell performs normal physiological roles S - is replicated in preparation for division G - chromatin condenses prior to division Cell Cycle -54-55 Madre Padre Centromere Sister chromatids Homologous Chromosomes Mitosis cell division in all body cells except the eggs and sperm Mitosis Prophase Chromosomes condense and nuclear breaks down. Spindle fibers grow from centrioles. Centrioles migrate to opposite poles of cell. Functions of mitosis growth of all tissues and organs after birth replacement of cells that die repair of damaged tissues 4 phases of mitosis prophase, metaphase, anaphase, telophase Metaphase Chromosomes lie along midline of cell. Some spindle fibers attach to kinetochores. Fibers of aster attach to plasma membrane. Anaphase Centromeres divide in two. Spindle fibers pull sister chromatids to opposite poles of cell. Each pole (future daughter cell) now has an identical set of genes. Telophase Chromosomes gather at each pole of cell. Chromatin decondenses. New nuclear appears at each pole. New nucleoli appear in each nucleus. Mitotic spindle vanishes. Figure 4.6 4-7 4-8
Mitosis: Prophase chromosomes shorten and thicken coiling into compact rods chromosomes two chromatids per chromosome one molecule of in each chromatid nuclear disintegrates and releases chromosomes into the cytosol centrioles sprout elongated microtubules spindle fibers push centrioles apart as they grow pair of centrioles lie at each pole of the cell some spindle fibers grow toward chromosomes and attach to the kinetochore on each side of the centromere spindle fibers push chromosomes to line up along the midline of cell Mitosis: Prophase Prophase Chromosomes condense and nuclear breaks down. Spindle fibers grow from centrioles. Centrioles migrate to opposite poles of cell. 4-9 Figure 4.6 () 4-0 Mitosis: Metaphase Mitosis: Anaphase Metaphase Chromosomes lie along midlineof cell. Some spindle fibers attach to kinetochores. Fibers of aster attach to plasma membrane. Anaphase Centromeres divide in two. Spindle fibers pull sister chromatids to opposite poles of cell. Each pole (future daughter cell) now has an identical set of genes. Chromatids Spindle fibers Figure 4.6 () 4- Figure 4.6 () 4- Ed Reschke Mitosis: Telophase chromatids cluster on each side of the cell rough ER produces new nuclear around each cluster chromatids begin to uncoil and form chromatin mitotic spindle breaks up and vanishes each nucleus forms nucleoli indicating it has already begun making RNA and preparing for protein synthesis 4- Cytokinesis cytokinesis the division of cytoplasm into two cells telophase is the end of nuclear division but overlaps cytokinesis early traces of cytokinesis visible in anaphase achieved by motor protein myosin pulling on microfilaments of actin in the terminal web of cytoskeleton creates the cleavage furrow around the equator of cell cell eventually pinches in two 4-4 4
Figure.: The stages of mitosis, p. 0. Figure.: The stages of mitosis (continued), p. 0. Centrioles (two pairs) Condensed Early mitotic chromatin spindle Pair of Fragments of centrioles nuclear Polar microtubules Metaphase plate Contractile ring at cleavage furrow Nuclear Centromere Plasma Chromosome, consisting membrane of two sister chromatids microtubule Spindle pole Spindle Daughter chromosomes Nuclear Interphase Early prophase Late prophase Metaphase Anaphase Telophase and cytokinesis Timing of Cell Division Cells divide when: they have enough cytoplasm for two daughter cells they have replicated their adequate supply of nutrients are stimulated by growth factor chemical signals secreted by blood platelets, kidney cells, and other sources neighboring cells die, opening space in a tissue Cells stop dividing when: snugly contact neighboring cells when nutrients or growth factors are withdrawn contact inhibition the cessation of cell division in response to contact with other cells 4-8 5