Asexual Reproduction Getting to the Details

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

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

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

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

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

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

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

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

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

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

More on Telophase Nucleoli reappear Mitotic Spindle disappears Cell elongation continues Mitosis is complete

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

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