Cell Cycle

• Genetic material


  Stored in the nucleus
• Traits and information for how an organism should grow

  Found as "genes" that are parts of chromosomes in the nucleus
• Every cell has chromosomes
• Chromosome


  A long piece of coiled DNA (deoxyribonucleic acid) and protein
• Levels of gene info in the nucleus

  • Gene (segment of DNA)
  • DNA
  • Proteins (multi folded with DNA)
  • Chromosomes (double stranded)
• Number of chromosomes between organisms can differ
• Typical human


  Has 46 chromosomes, 23 pairs
• Average butterfly


  Has 380 chromosomes
• Chromosomes


  Only visible when the cell is dividing
• When not dividing, the DNA and protein making up the chromosome


  Are spread through the cell as chromatin
• Chromatin


  Are like long thin threads
• When the cell is dividing, chromatin


  Coils up into a pair of sister chromatids
• Sister chromatids


  Condense and become visible, short, thick chromosomes
• Sister chromatids


  Are held together by a centromere
• Types of cells


  • Sex cells (gametes)
  • Somatic cells (everything else)
• Gametes


  Egg (ovum) and sperm cells, specialized reproductive cells that unite to produce a zygote
• Gametes


  Have a haploid number (n) of chromosomes
• Cell division


  1. Interphase

  2. Cell division
• Interphase


  Growth stage, 90% of the cycle
• Cell division


  Division (mitosis), 10% of cycle
• Parts of interphase


  • G1 - cell growth
  • S - synthesis of DNA (replication)
  • G2 - growth and prep for mitosis
• Chromosomes are only duplicated during S phase
• Purpose of cell division

  • Growth
  • Replace dead/ damaged cells
• MITOSIS


  1. Break down of nuclear membrane

  2. Spindle fibers appear

  3. Chromosomes condense into sister chromatids

  4. Centrioles move to opposite poles

  5. Chromosomes align across the center

  6. Spindle fibers attach to centromeres

  7. Centromeres divide, sister chromatids move to opposite poles

  8. Nuclear membrane re forms

  9. Spindle fibers disappear

  10. Chromosomes uncoil
• CYTOKINESIS


  Division of cytoplasm into 2 separate cells
• Animal cell division


  Cleavage furrow pinches cell
• Plant cell division


  Cell plate forms between to form a new cell wall
• Hayflick limit


  Human cells on average stop dividing after around 52 divisions
• Senescent cell


  The cell that has stopped dividing when the telomere (protective bits on DNA at the end of each chromosome) shortens enough to the point that it is consumed