Cell Division & Mitosis RUSSELL BIOLOGY RHODES AP BIO

Multicellular organisms are made of cells and cell products Multicellular organisms have divided from a single cell Most cells are specialized Regeneration is a limited property Cells must form 3-D organism with specialized tissues in specific locations Zebra fish (Danio rerio) grows new fin when attacked by Knifefish (Notopterus notopterus)

10.1 Overview: The Cycle of Cell Growth and Division  STEPS  Cell growth and everyday activity like making proteins from accessible DNA regions called genes and making of new organelles and structures  DNA replication  DNA (chromosomes) segregated into equal parts; even distribution  DNA moved into two new nuclear regions  Cytoplasm divided; fairly even distribution  2 new cells; genetically identical to each other and the parent  PURPOSES  Growth  Maintenance  Repair  Reproduce

Concepts  DNA is chemical that stores information  Genes are regions of chromosomes that code for proteins  A-T, C-G (Purines and pyrimidines)  Double helix  Chromosomes are individual and linear  Replication  Chromosomes that have replicated are called sister chromatids and are joined at kinetochores by centromeres, forming arms

 Cell division is used for  Growth = larger organisms  Replacement = due to wear and tear  Repair = to fix wounds  Reproduction of single celled eukaryotes  Duplicates  Chromosomes are replicated  Cells produced are identical genetically to each other AND to the cell produced  In meiosis cells generated have potential to be genetically different and contain ½ the DNA of the parent cell = gametes  Partitioning of Chromosomes  2 copies of each chromosome = Diploid;  These are homologous meaning they have the same genes in the same positions and sequences  1 copy of each chromosome = haploid  “ploidy “ refers to chromosome sets  Chromosomes replicate into sister chromatids ( for a phase there are 4 of each)  Sister chromatids move apart in Segregation  Each cell gets one of each set of chromatids; pairs of homologous chromosomes creating CLONES

10.2 Overview: The Mitotic Cell Cycle  Cell Cycle = Interphase + Mitosis + Cytokinesis  Interphase  Between NUCLEAR divisions  Phases of Mitosis  Prophase  Prometaphase  Metaphase  Anaphase  Telophase  Cytokinesis  Animal cells “furrow” with a band of microfilaments pinching the cell into two  Plant cells deposit material for new cell wall starting at midpoint

Concepts  Chromatid  Kinetochore  Spindle  Centrosome  centriole  Microtubules  Metaphase plate (plane)  Segregation  Page 207

 Interphase = between divisions  G1 = chromosomes as chromatin, dark nucleus, everyday protein synthesis; cell growth  S= synthesis or REPLICATION of DNA; chromosomes are sister chromatids  G2 = cohesions; centrosomes have replicated; new organelles  G0 = sometimes cells are suspended and won’t divide again (not the typical scenario)  Mitosis= division of eukaryotic nucleus  Prophase= chromosomes visible (chromatids); nucleus disintegrating; centrosomes moving and creation of spindle occurring  Prometaphase= nucleus gone, spindle formed; kinetochores attached to spindle; tugging starts to move chromosomes to metaphase plane  Metaphase= chromosomes aligned at spindle midpoint  Anaphase= kinetochores separate and chromatids/ now chromosomes move toward poles along the spindle microtubules; cohesions are cut  Telophase= two separate nuclei (piles of chromosomes at the poles) now begin to uncoil and become chromatin, nuclei are rebuilt; cytokinesis has started; clones will be created  Cytokinesis= physical division of cytoplasm  Animal = cleavage furrow  Plant= cell plate

10.3 Overview: Formation and Action of the Spindle  Plant cells  No centrosomes – spindle forms around nucleus  Animal cells  Centrosomes divide and two parts move apart  Microtubules form creating the spindle  Kinetochore microtubules  Pole to kinetochore of chromosome  Motor proteins of kinetochore WALK chromosome along microtubule  Motor proteins at poles pull kinetochore microtubules  Movement is species and cell-type specific  Anaphase  Non-kinetochore microtubules  Pole to overlap region at metaphase plane without chromosomes  Overlap region is reduced and cell lengthens

10.4 Overview: Cell Cycle Regulation  Check points for starting critical phases  Internal check points  Cyclin and cyclin dependent protein kinases (Cdk)  Cyclin + phosphate (phosphorylation) = Cdk  Initiate or regulate 4 key events  G1, G1/S, S and M  External check points  Surface receptors and binding sites for proteins  Growth hormones, peptide hormones, surface groups, matrix  Speed/ slow/ stop  Contact inhibition  Cancer  Control of cell cycle is lost, continuous and uncontrolled growth of cells = mass  oncogenes

SEE PAGE 217  Control proteins called Cyclins regulate function of many checkpoints  Cyclins are proteins (work based on concentration) and Cdk are enzymes (function when phosphorylated and connected to cyclin) and cause action to occur  1. G1/S checkpoint  Cell is stopped ; waiting for extracellular signals, checking for DNA damage; needs growth factor to procede.  MAIN check point; once past G1/ S committed to mitosis  2. G2/M checkpoint  Stopped before Mitosis if DNA didn’t replicate  Insure identical daughter cells  3. Mitotic Spindle checkpoint  Check at metaphase to see if chromosomes and kinetochores attached to spindle; insures even distribution of DNA  MPF Maturation Promoting Factor

10.5 Overview: Cell Division in Prokaryotes  Replication of DNA caused by enzymes  Two circles of DNA migrate to opposite ends of cell  Move as they are attached to CM and cell is elongating  CW grows inward to create two cells  “ Theta replication”  “Binary fission”