Chapter 11 lecture

• Cell Cycle


  The life of a cell from when it is formed until it divides
• Purpose of Cell Division

  • Growth & Development
  • Repair
• Eukaryotic Cell Division


  • More complex & slower
  • Occurs in response to internal signals
  • Reproduce the entire organism for single-celled eukaryotes
  • Result in more cells within a multicellular organism (not always clones of original)
• Prokaryotic Cell Division


  • Rapid
  • Occurs in response to environmental signals
  • Asexual reproduction results in 2 new cells (clones of original)
• Prokaryotic Chromosome


  • Single, often circular
  • ori - where replication starts
  • ter - where replication ends
• Prokaryotic Cell Division


  1. Replication complete

  2. ori regions move toward opposite ends of the cell

  3. Segregating daughter DNA molecules
• Somatic Cells


  • Non-reproductive cells
  • Have two sets of chromosomes (2n = diploid)
• Gamete Cells


  • Reproductive
  • Have half as many chromosomes as somatic cells (n = haploid)
• Chromosomes


  Condensed DNA wrapped around histones, collectively known as chromatin
• Cell Cycle


  1. Mitotic (M) phase

  2. Interphase - G1 phase, S phase, G2 phase
• Mitosis


  1. Division of genetic material

  2. Cytokinesis - division of the cytoplasm
• Mitotic Spindle


  • Structure of microtubules that controls chromosome movement during mitosis
  • Includes centrosomes, spindle microtubules, and asters
• Mitosis


  1. Prometaphase - some spindle MT attach to kinetochores & move the chromosomes

  2. Metaphase - chromosomes lined up at the metaphase plate

  3. Anaphase - cohesins cleaved by separase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cell

  4. Telophase - genetically identical daughter nuclei form at opposite ends of the cell
• Cytokinesis in Animal Cells

  Occurs by a process known as cleavage, forming a cleavage furrow
• Cytokinesis in Plant Cells

  A cell plate forms
• Cell Cycle Control System

  • Regulated by both internal and external controls
  • Has specific checkpoints where the cell cycle stops until a go-ahead signal is received (G1, G2, and M phases)
• Cyclins and Cyclin-Dependent Kinases

  • Two types of regulatory proteins involved in cell cycle control
  • The activity of a Cdk rises and falls with changes in concentration of its cyclin partner
  • MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell's passage past the G2 checkpoint into the M phase
• Meiosis


  • Sexual reproduction gives rise to genetically unique offspring
  • Reduces the number of chromosomes by half (2n to n)
  • Preceded by the replication of chromosomes
  • Results in four haploid daughter cells
  • Takes place in two consecutive cell divisions, called meiosis I and meiosis II
• Meiosis I


  Separation of Homologous Chromosomes
• Meiosis II


  Separation of Sister Chromatids
• Genetic Variation


  • Crossing Over
  • Independent Assortment of Chromosomes
  • Random Fertilization
• Crossing Over


  • Occurs during Prophase I (Chiasmata)
  • Occurs between Nonsister Chromatids
  • Results in recombinant chromosomes
• Mitosis


  Cell division resulting in two identical daughter cells, each with the same number and type of chromosomes as the parent cell. Occurs in somatic cells.
• Meiosis


  Cell division resulting in four non-identical daughter cells, each with half the number of chromosomes as the parent cell. Occurs in reproductive organs for sexual reproduction.
• Number of daughter cells in mitosis

  Two
• Number of daughter cells in meiosis

  Four
• Number of chromosomes in mitosis daughter cells


  Same as parent cell
• Number of chromosomes in meiosis daughter cells

  Half the number as parent cell
• Meiosis location


  Reproductive organs (gametes) of sexually reproducing organisms.
• Meiosis in animals


  Occurs in the testes of males and the ovaries of females.
• Meiosis in plants


  Occurs in the anthers of male flowers and the ovules of female flowers.
• Chromatids are identical copies of DNA that form during S phase.
• Chromatids are identical copies of DNA that have not yet separated from one another.