Asexual Reproduction

1
Asexual Reproduction

• Getting to the Details

2
Asexual Reproduction in Prokaryotes

• Binary Fission
• Prior to division, an exact copy of DNA is made
• Each copy attaches to a different point on plasma
  membrane
• Cell stretches out and pinches in two

3
Asexual Reproduction in Eukaryotes

• The Cell Cycle or life cycle of cell can range
  from 16 hours to days, to a lifetime
• Eukaryotic Cells are more complex, so process of
  cell division is more complicated

4
First Stage of Interphase

• G1 - Gap 1 Begins at the end of cell division
• This is the time for cell growth and activity
• This stage can be extended if environmental
  factors are not favorable

5
Second Stage of Interphase

• S - Synthisis
• The DNA replicates or makes a copy of itself
  during this stage
• Each chromosome now consists of two sister
  chromatids

6
Third Stage of Interphase

• G2 Gap 2
• Centrioles replicate, and begin to separate
• Centriole pairs produce centrosomes spindle
  organizing centers
• The nucleolus produces ribosomes for increasing
  protein synthesis needed for growth

7
Mitosis Begins Prophase

• Changes in the Nucleus
• Chromatin condenses to become visible
• Sister chromatids join together at centromere
• The Nucleolus disappears
• Nuclear membrane begins to dissolve

8
Prophase Continued

• Changes in the cytoplasm
• Centrosomes move to opposite sides to the cell
  forming poles
• Mitotic spindles grow out from the centrosomes
• Each chromosome attaches to a spindle fiber
  microtubule
• Chromosomes begin to move toward the middle of
  the cell

9
Metaphase

• The mitotic spindle is complete
• Chromosomes are all lined up on the metaphase
  plate at the middle of the cell
• The sister chromatids face opposite poles.
• Each member of the pair is attached to a spindle
  fiber heading in the opposite direction

10
Anaphase

• Anaphase begins when the two centromeres of each
  chromosome come apart
• The sister chromatids separate and are pulled by
  the spindle fiber to opposite poles
• Each sister chromatid is now considered a
  complete daughter chromosome
• The cell begins elongating

11
Telophase

• Telophase is roughly the reverse of prophase
• Daughter nuclei appear at opposite poles as
  nuclear membrane forms around chromosomes
• Chromatin uncoils so chromosomes no longer
  visible

12
More on Telophase

• Nucleoli reappear
• Mitotic Spindle disappears
• Cell elongation continues
• Mitosis is complete

13
Cytokinesis

• The cytoplasm divides equally
• In animals, a cleavage furrow forms, pinching the
  cell in two
• In plants, a cell plate forms between new cells,
  forming a cell wall

14
Mistakes in Mitosis

• Cancer occurs when cell cycle regulation
  malfunctions
• Cells divide rapidly, forming abnormal tissue or
  tumors
• Current research is focusing on cell cycle
  regulation
• Most chemotherapies work by disrupting cell
  division and the formation of the spindle fibers