Cell Cycle

• Rudolf Virchow: '“omnis cellula e cellula”'
• Cell Cycle


  Series of growth and development between birth and reproduction
• Key Roles of Cell Division

  • The ability of organisms to produce more of their own kind best distinguishes living things from nonliving matter
  • The capacity to procreate has a cellular basis
  • The continuity of life is based on the reproduction of cells, or cell division
• In unicellular organisms, division of one cell reproduces the entire organism
• Functions of cell division in multicellular organisms

  • Development from a fertilized cell
  • Growth
  • Repair
• Cell division


  Integral part of the cell cycle, the life of a cell from formation to its own division
• Passing identical genetic material to cellular offspring is a crucial function of cell division
• Outline of topics related to the cell cycle

  • Chromosome Structure
  • Prokaryotic vs. Eukaryotic Cell Division
  • Phases of the Cell Cycle
  • Controlling the Cell Cycle
  • Cancer and the Cell Cycle
  • Meiosis
• All the DNA in a cell constitutes the cell’s genome
• Chromosomes are discrete DNA structures within cells that control cellular activity
• First observed by Walter Fleming on rapidly dividing cells of Salamander larvae


  1882
• Chromosome number in different organisms

  • S. cerevisiae: 2n=1262
  • D. melanogaster
  • P. troglodytes
• Prokaryotes


  Single, double-stranded DNA, nucleoid region containing the genetic material, extrachromosomal DNA found in Plasmid
• Eukaryotic Cell Chromosome


  Linear, double-stranded, consists of several DNA molecules located inside a nucleus, consists of chromatin which becomes densely coiled, folded, and condensed to form a chromosome after duplication
• Distribution of Chromosomes During Eukaryotic Cell Division

  Homologous chromosomes, diploid cells, replication of homologues into sister chromatids, separation during cell division, centromere as the narrow “waist” of the duplicated chromosome
• Types of Cell Reproduction

  • Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells
  • Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells
• Cell Division in Prokaryotes

  Binary fission, single chromosome makes a copy of itself, cell wall forms between the chromosomes dividing the cell
• Schizogony


  Form of reproduction forming many daughter cells produced from the parent cell, nucleus undergoes repeated division to produce many nuclei
• Other Forms of Asexual Reproduction

  • Budding- new organism develops from a bud of an existing organism
  • Regeneration- the organism is capable of regro
• Asexual reproduction


  1. Form of reproduction forming many daughter cells produced from the parent cell

  2. Nucleus undergoes repeated division to produce many nuclei
• Other Forms of Asexual Reproduction

  • Budding- new organism develops from a bud of an existing organism
  • Regeneration- the organism is capable of regrowing certain body parts
  • Fragmentation- organisms split into two or more fragments to become new individuals
• Ways asexual reproduction takes place in plants

  • Natural (self-propagation): Ginger, onion, potato grow from buds, Sweet potato/Strawberry from stolons
  • Artificial Methods: Cutting (plant is cut along the node), Grafting (two different plants are joined together)
• The rooted plant is known as the stock


  The other plant is known as the scion
• Cell Cycle


  • An ordered series of events involving cell growth and cell division
  • A precise timed and carefully regulated stages of growth, DNA replication, and division that produce two genetically identical cells
• Phases of the Cell Cycle

  • G1 phase (“first gap”)
  • S phase (“synthesis”)
  • G2 phase (“second gap”)
  • M phase
• Events of the Cell Cycle: G1 phase


  Cell increases in size, produces all the structures it needs to carry out its functions
• Events of the Cell Cycle: S phase

  DNA synthesis takes place, results in the formation of two identical copies of each chromosome-sister chromatids, centrosome is duplicated during the S phase
• Events of the Cell Cycle: G2 phase


  Organelles and molecules required for cell division are produced
• The Mitotic Phase


  A multistep process during which the duplicated chromosomes are aligned, separated, and moved to opposite poles of the cell, and then the cell is divided into two new identical daughter cells
• Mitosis


  Division of the nucleus
• Prophase


  Chromatin in nucleus condenses to form visible chromosomes, Duplicated chromosomes appear as two identical sister chromatids, Nuclei disappear, Spindle apparatus begins to form, Kinetochore, Golgi and ER are dispersed, Nuclear envelope breaks down
• Prometaphase


  Chromosomes continue to condense, Mitotic spindle continues to develop, Centrioles reach the poles of the cell, Nuclear membrane disintegrates
• Metaphase


  The chromosomes line up across the center of the cell, Chromosomes convene at the metaphase plate, a line at the middle of the cell, Chromosomes, attached to the kinetochore fibers, move to the center of the cell
• Anaphase


  The sister chromatids separate into individual chromosomes, Pulled apart to opposite poles of the cell by kinetochore fibers
• Telophase


  Chromosomes gather at opposite ends of the cell and lose their distinct shape, Spindle disassembles, Nuclear envelope forms around each set of chromosomes
• Anaphase


  1. The sister chromatids separate into individual chromosomes

  2. Pulled apart to opposite poles of the cell by kinetochore fibers
• Telophase


  1. Chromosomes gather at opposite ends of the cell and lose their distinct shape

  2. Spindle disassembles

  3. Nuclear envelope forms around each set of sister chromatids

  4. Nucleolus reappears

  5. Chromosomes become less condensed
• Cytokinesis


  1. The cytoplasm pinches in half

  2. Results in two separate daughter cells with identical nuclei

  3. Each daughter cell has an identical set of duplicate chromosomes
• Cytokinesis in Animal Cells

  1. Cleavage furrow forms to split cell

  2. Formed by a contractile ring of actin filaments

  3. Eventually pinches mother cell in two
• Cytokinesis in Plant Cells

  1. Cell plate forms at the equator to divide cell

  2. The membranes of the cell plate become the plasma membrane between the daughter cells

  3. Contents of vesicles become the middle lamella between the two daughter cells