Lecture 2 Cell Cycle Life Cycle

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					Botany 10                        Dr. Bibit Traut             Spring 2009


    Lecture 2: Cell Cycle & Life Cycle
                             Cell Cycle
Interval of time between formation of a cell & its division to form 2 new
cells
Plants with more DNA in nuclei have longer cell cycles (lasts hours-days)
Includes:
  cell growth
  duplication
Process occurs in special regions—“meristems”

                             Cell Cycle
Interphase: cells not dividing
  G1 - Cell increases in size
  S - DNA replication takes place
  G2- Mitochondria divide, microtubules produced
Mitosis: cells dividing
Cytokinesis: division of cell cytoplasm, plasma membrane

                             Cell Cycle
                       DNA Replication
ALL cells need instructions (DNA)
Before cell divides, need copy of DNA for each cell (replication)

            DNA packaged in Chromosomes

                       DNA Replication
Replication occurs in uncondensed DNA—not in the condensed form with
chromatin

                             DNA
                           Replication
Botany 10                      Dr. Bibit Traut              Spring 2009

                       DNA vocabulary
Chromatin—uncoiled, protein-bonded DNA
Chromosome
                               Mitosis
Purpose – separate doubled DNA in nucleus of cell
Four phases
  Prophase
  Metaphase
  Anaphase
  Telophase
                               Prophase
                             “plain to see”
chromosomes condense
nuclear envelope breaks down
spindle fibers (microtubules) formed

                              Metaphase
                              “middle”
chromosomes aligned in the middle of cell, with each sister chromatid
facing opposite poles
Chromatids joined at centromere

                              A naphase
                               “apart”
sister chromatids separate
moves to opposite pole
                              Telophase
                             “two nuclei”
chromosomes de-condense
spindle breaks down
nuclear envelope forms

                              Cytokinesis
Botany 10                           Dr. Bibit Traut         Spring 2009


Life Cycles: Meiosis & the Alternation
            of Generations
                              Life Cycles
Transfer of genetic information from parent to offspring
Two types of reproduction
  Asexual reproduction (“vegetative”)
  Sexual reproduction


                      Plant Reproduction

                    Asexual Reproduction
Each generation genetically identical
Occurs in unicellular and multicellular organisms
Mitosis = mechanism

            Examples of Asexual Reproduction
Strawberry plants → stolons or runners
Redwood tree → dormant buds under bark at base of tree are stimulated to
grow when tree is killed by fire or removed by timber harvest
Trembling aspen → produce special roots that grow horizontally, roots
periodically give rise to stems some distance from parent tree

                    Asexual Reproduction
Advantages
  Only 1 parent required
  Produces offspring adapted to habitat
  Generates offspring fast
  Costs less metabolically
Disadvantage
  Genetic diversity remains fixed
Botany 10                           Dr. Bibit Traut    Spring 2009

                        Sexual Reproduction
Each generation is genetically unique
Occurs in unicellular & multicellular organisms
Meiosis = mechanism
  Reduces chromosome number by half
  Produces gametes (haploid=1n)


                        Sexual Reproduction
Advantages
  Genetic diversity → adaptive
  Dispersal
Disadvantages
  bringing gametes together
  Reducing chromosomes, but fertilization restores #

                        Sexual Reproduction
Chromosome set
  Consists of one chromosome of each kind
Haploid
  Any cell with just one set of chromosomes
  1n
Diploid
  A cell with 2 chromosome sets
  2n
  Zygote formed by union of two gametes is diploid


                            DNA vocabulary
Chromatin—uncoiled, protein-bonded DNA
Chromosome
                         Mitosis vs. Meiosis
                                   Meiosis I
                                  Meiosis II
                              Crossing Over
Botany 10                        Dr. Bibit Traut      Spring 2009

              Sources of Genetic Variation
Independent assortment
Crossing over
Genetic recombination (sexual reproduction)

                Alternation of Generations
Refers to creation of both diploid & haploid bodies
Sporophyte
  Produces spores via meiosis
Gametophyte
  Produces gametes via mitosis