Cell Cycle

• Chromatin


  A mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms

  
• Chromatid


  One of the two identical genetic components of a chromosome after DNA replication, prior to cell division

  
• Chromosome


  The condensed structure of DNA and associated proteins in the nucleus of eukaryotic cells, which carries the genes

  
• Cell Cycle


  The orderly sequence of events in which a cell duplicates its contents and then divides in two

  
• Cell Cycle


  1. Duplication of genetic code and organelles

  2. Division to evenly distribute duplicated contents

  
• Cell Cycle


  • Allows unicellular organisms to produce new organisms
  • Allows multicellular organisms to produce functioning organisms
• Cell Cycle Regulation


  1. G1 phase (cell growth)

  2. S phase (DNA replication)

  3. G2 phase (preparation for mitosis)

  4. M phase (mitosis and cytokinesis)

  
• The mitotic phase alternates with interphase in the cell cycle

  
• Interphase


  The "intermission" or "in-between" phase of the cell cycle, including G1, S, and G2 phases

  
• G0 Phase


  The resting phase where the cell exits the cell cycle and usually does not reproduce again
• Mitosis


  1. Prophase

  2. Metaphase

  3. Anaphase

  4. Telophase

  5. Cytokinesis

  
• Prophase


  • Chromatin condenses into chromosomes
  • Mitotic spindle fibers form from centrosomes

  
• Metaphase


  • Chromosomes line up at the equatorial or metaphase plate
• Anaphase


  • Sister chromatids separate and move to opposite poles of the cell
• Telophase


  • Spindle fibers disappear, two daughter nuclei form, and chromosomes return to chromatin
• Cytokinesis


  The division of the cytoplasm to form two distinct, identical daughter cells
• Cytokinesis in Animal Cells

  • Cleavage furrow forms and pinches the cell in two
• Cytokinesis in Plant Cells

  • Cell plate forms from Golgi vesicles at the middle of the cell
• Somatic cells and sex cells (gametes) are the two types of body cells in sexually reproducing eukaryotes
• Prometaphase


  1. Mitotic spindle is starting to form

  2. Discrete chromosomes are seen, each consisting of two identical sister chromatids

  3. Nuclear envelope will fragment later in prometaphase

  
• Metaphase


  1. Spindle is complete

  2. Chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate

  
• Anaphase


  1. Chromatids of each chromosome have separated

  2. Daughter chromosomes are moving to the ends of cell as their kinetochore microtubules shorten

  
• Telophase


  1. Daughter nuclei are forming

  2. Cell plate, which will divide the cytoplasm in two, is growing toward the perimeter of the parent cell

  
• Somatic cells


  Body cells
• Sex cells (a.k.a. gametes, germline)

  Reproductive cells
• Sexually reproducing eukaryotes have two types of body cells: somatic cells and sex cells
• Meiosis


  Cell division of gametes
• Haploid


  One copy of each chromosome
• Diploid


  Two sets of chromosomes
• Homologues


  Chromosomes that exist in pairs in diploid cells, except for sex chromosomes
• Karyotype


  • Karyotype 1
  • Karyotype 2
• Sexual reproduction


  Fusion of two gametes to produce a single zygote
• Sexual reproduction introduces greater genetic variation and allows genetic recombination
• At fertilization, 23 chromosomes are donated by each parent, resulting in a diploid zygote with 46 chromosomes (23 pairs)
• Gametes (sperm/ova) contain 22 autosomes and 1 sex chromosome, and are haploid (n=23 in humans)
• Most cells in the body are produced through mitosis, not meiosis (only gametes are produced through meiosis)

  
• Meiosis I


  Meiosis II
• Meiosis shuffles the genes through crossing over in Prophase I and independent assortment in Metaphase I
• Crossing over


  Homologues break at identical locations and rejoin opposite partners, creating new combinations of alleles
• Independent assortment


  Random assortment of chromosomes during meiosis, resulting in unique combinations of genes in gametes