© John Wiley & Sons, Inc. Chapter 2Cellular Reproduction
© John Wiley & Sons, Inc. Chapter Outline • Cells and Chromosomes • Mitosis • Meiosis • Life Cycles of Some Model Genetic Organisms
In both prokaryotic and eukaryotic cells, the genetic material is organized into chromosomes. © John Wiley & Sons, Inc. Cells and Chromosomes Eukaryotic: 23, non-circular, linear Prokaryotic: 1, circular Viruses: 1, DNA circular; 1, RNA linear
© John Wiley & Sons, Inc. The Cellular Environment • Cytoplasm / cytosol / Nucleus/ …the inside of a cell….. Plasma membrane….the outside of the cell… • Water ( 70-80 %) • Hydrophilic and Hydrophobic Molecules; Amphiphatic • Carbohydrates (Glucose and Glycogen) • Lipids (Cholesterol, phospholipids and fatty acids)
The Cellular Environment Proteins (amino acids to polypeptide), including enzymes Ribonucleoproteins, including RNAse as an enzyme Membrane—made of lipids and proteins Cell Wall: cellulose [murein-(sugars and amino acid)-in bacteria) © John Wiley & Sons, Inc.
Animal and Plant Cells Organelles: © John Wiley & Sons, Inc.
© John Wiley & Sons, Inc. Animal and Plant Cells No Organelles:
Animal and Plant Cells © John Wiley & Sons, Inc.
© John Wiley & Sons, Inc. Chromosomes • Double-stranded DNA with associated proteins and sometimes RNA • Prokaryotic cells contain one circular chromosome plus smaller plasmids ( ?) • Most eukaryotic cells contain several large linear chromosomes plus a circular mitochondrial DNA
© John Wiley & Sons, Inc. Vocabulary for Chromosomes • Diploid: cells with 2 copies of each chromosomes • Haploid: cells with one copy of each chromosomes • Somatic cells: any cells of an organism, diploid and go under mitosis. • Germ line: reproductive cells that give rise to gametes • Gametes: specialized cells (sperm and ova) • Centromere: point of interaction of each chromosomes; region of chromosomes required for its movement.
© John Wiley & Sons, Inc. Cell Division in Prokaryotes:Fission • A mother cell divides to produce two daughter cells. • The mother cell’s chromosome is duplicated prior to fission. • Each daughter cell receives one copy of the chromosome and more or less the rest of the content. • Clone—a population of genetically identical cells. • Colony—a visible mass of cells (1 to 250 cells).
Division time? http://mitosissection2.tumblr.com/
© John Wiley & Sons, Inc. Cell Division in Eukaryotes:Inter (I) Phase and Mitosis (M) Phase Go 30 min to
© John Wiley & Sons, Inc. • Cells, the basic units of all living things, are enclosed by membranes. • Chromosomes, the cellular structures that carry the genes, are composed of DNA and protein. • In eukaryotes, chromosomes are contained within a membrane-bounded nucleus; in prokaryotes they are not. • Eukaryotic cells possess complex systems of internal membranes as well as membranous organelles such as mitochondria, chloroplasts, and the endoplasmic reticulum.
© John Wiley & Sons, Inc. • Haploid eukaryotic cells possess one copy of each chromosome; diploid cells possess two copies. • Prokaryotic cells divide by fission (binary) • Eukaryotic cells divide by mitosis and meiosis. • Eukaryotic chromosomes duplicate when a cell’s DNA is synthesized; this event is characteristic of the S phase of the cell cycle.
When eukaryotic cells divide, they distribute their genetic material equally and exactly to their offspring. © John Wiley & Sons, Inc. Mitosis Inter-phase: Chromatin---Heterochromatin ---Eurochromatin M-phase: Chromosomes
© John Wiley & Sons, Inc. Mitosis in Animal Cells mechanical force?
© John Wiley & Sons, Inc. Microtubules, Centrosomes and Centrioles.
Centrosome duplicates (S phase) Centrosomesmove to opposite sides of nucleus during prophase. Mitotic spindle assembles (microtubules=MT) Microtubule organizing centers (MTOCs)
SpindleMTs make contact with chromosomes ---centromere (sequence repeated DNA sequence=heterochromatin =CEN sequences) ---kinetochore (protein-like containing structure)
© John Wiley & Sons, Inc. Cytokinesis inAnimal and Plant Cells Cleavage furrow associated with the contractile ring (Actin and Myosin)
© John Wiley & Sons, Inc. • As a cell enters mitosis, its duplicated chromosomes condense into rod-shaped bodies (prophase). • As mitosis progresses, the chromosomes migrate to the equatorial plane of the cell (metaphase). • Later in mitosis, the centromere that holds the sister chromatids of a duplicated chromosome together splits, and the sisters chromatids separate (or disjoin) from each other (anaphase)
© John Wiley & Sons, Inc. • As mitosis comes to an end, the chromosomes decondense and a nuclear membrane reforms around them (telophase). • Each daughter cell produced by mitosis and cytokinesis has the same set of chromosomes; thus, daughter cells are genetically identical.
Sexual reproduction involves a mechanism that reduces the number of chromosomes by half. © John Wiley & Sons, Inc. Meiosis
© John Wiley & Sons, Inc. Homologues Xx or Xy
© John Wiley & Sons, Inc. Comparison ofMitosis and Meiosis Non-reduction Reduction
© John Wiley & Sons, Inc. Prophase I: Leptonema • Chromosomes condense • Each chromosome has two sister chromatids
© John Wiley & Sons, Inc. Prophase I: Zygonema • Synapsis (pairing) of homologous chromosomes • Synaptonemal complex
© John Wiley & Sons, Inc. The Synaptonemal Complex Function ? Structural...
© John Wiley & Sons, Inc. Prophase I: Pachynema • Chromosomes condense further • Bivalent of chromosomes • Tetrad of chromatids • Crossing over occurs • (exchange material)
© John Wiley & Sons, Inc. Prophase I: Diplonema • Paired chromosomes separate slightly but are in contact as chiasmata
© John Wiley & Sons, Inc. Chiasmata
© John Wiley & Sons, Inc. Prophase I: Diakinesis • Nuclear envelope fragments • Spindle fibers (MT) attach to kinetochores • Chromosomes move to central plane in pairs
© John Wiley & Sons, Inc. Metaphase I • Paired chromosomes are oriented toward opposite poles • Terminalization: chiasmata move toward telomeres • Why?
© John Wiley & Sons, Inc. Anaphase I • Chromosome disjunction (separation of paired chromosomes) • Separated homologues move toward opposite poles
© John Wiley & Sons, Inc. Telophase I • Chromosomes reach the poles; nuclei forms • Spindle apparatus is disassembled • Daughter cells separated by membranes • Chromosomes decondense • Each chromosome still has two sister chromatids
© John Wiley & Sons, Inc. Prophase II • Chromosomes condense • Chromosomes attach to a new spindle apparatus • Sister chromatids are attached to spindle fibers from opposite poles
© John Wiley & Sons, Inc. Metaphase II • Chromosomes align at equatorial plane
© John Wiley & Sons, Inc. Anaphase II • Centromeres split • Chromatid disjunction—sister chromatids move toward opposite poles
© John Wiley & Sons, Inc. Telophase II • Separated chromatids gather at poles; daughter nuclei form • Each chromatid is now called a chromosome • Each daughter nucleus contains a haploid set of chromosomes
© John Wiley & Sons, Inc. Cytokinesis
© John Wiley & Sons, Inc. Daughter cells are NOT genetically identical • Maternal and paternal homologues synapse, then disjoin independently. • Homologous chromosomes exchange material by crossing over
© John Wiley & Sons, Inc. • Diploid eukaryotic cells form haploid cells by meiosis, a process involving one round of chromosome duplication followed by two cell divisions (meiosis I and meiosis II). • During meiosis I, homologous chromosomes pair (synapse), exchange material (cross over), and separate (disjoin) from each other. • During meiosis II, chromatids disjoin from each other.
© John Wiley & Sons, Inc. Human 23 3,200 20 to 25,000
© John Wiley & Sons, Inc. Life Cycle ofSaccharomyces cerevisiae (yeast).
© John Wiley & Sons, Inc. Arabidopsis thaliana, plant
© John Wiley & Sons, Inc. Spermatogenesis and Oogenesis in Mammals