BIO 110

Dr. Ely

Chapter 8Notes – Cellular Reproduction and Mitosis

  1. In eukaryotes, DNA is organized into separate chromosomes
  2. A chromosome is a molecule of DNA that is wrapped around proteins called histones
  3. Chromatin is the “loose” form of the chromosome – this is the form of chromosomes when the cell is not dividing.
  4. A Chromatid is a highly compact form of chromosomes – this is the form chromosomes take during cell division.
  5. Sister chromatids are the products of DNA replication
  6. They are identical chromosomes created through replication
  7. Held together by a bundle of proteins called the centromere, which gives them the characteristic “X” shape of chromosomes.
  1. The Cell Cycle is a sequence of stages through which a cell goes from the time it arises via division to the time it divides again
  2. Cell division is necessary for growth of an organism and for maintenance – the replacement of cells that die
  3. Interphase – non-dividing period
  4. G1 phase: The newly-formed cell begins to synthesize proteins and carry out its specific functions
  5. S phase: “synthesis” phase where DNA replication occurs (sister chromatids form); normal functions are temporarily suspended
  6. G2 phase: the cell returns to its normal functioning but it also prepares for cell division by forming the cytoskeletal structures needed
  7. M (mitotic) phase – dividing period
  8. Mitosis – division of the nucleus; copies of chromosomes are separated and encapsulated into two new nuclei
  9. Cytokinesis – division of the cytoplasm; 2 new daughter cells are formed
  1. Mitosis has four different phases
  2. Prophase
  3. Chromosomes condense into sister chromatids
  4. Nuclear envelope (the nuclear membrane) begins to dissolve
  5. Centrosomes move to opposite poles of the cell and spindle fibers begin to form between them
  6. Centrosomes are microtubule-organizing centers; the microtubules will grow from centrosomes at either end, or pole, of the cell and stretch across to attach to the chromosomes
  7. Spindle fibers are another name for these microtubules because once they are fully formed, the entire structure is called the mitotic spindle
  1. Metaphase
  2. Chromosomes line up down the center of the cell, called the spindle equator
  3. The nucleus is completely gone
  4. Spindle fibers are fully formed and attached to the centromeres of each chromosome
  5. Anaphase
  6. Sister chromatids separate (becoming “daughter chromosomes”) to the opposite poles: each chromatid is pulled away from its sister as the centromeres are pulled by the spindle fibers
  7. The nucleus is still gone
  8. Spindle fibers begin to disassemble
  1. Telophase
  2. Chromosomes begin to loosen, they return to chromatin form
  3. A nuclear envelope begins to form around each group of chromosomes; in other words, two new nuclei form
  4. Spindle fibers disappear
  1. Cytokinesis differs between plants and animals
  2. Cytokinesis typically overlaps with telophase
  1. A cleavage furrow forms in animal cells
  2. A contracting ring of actin filaments creates a divide
  3. The cells are squeezed apart
  1. A cell plate forms in plants
  2. The cell wall is a physical boundary that prevents the squeezing apart of two new cells
  3. Vesicles from the Golgi bodies on either side of the cell merge at the middle to form new cell membranes for each new cell – the newly formed membrane layer is the cell plate
  4. Membrane molecules build new cell walls after the cell plate has formed