Cell Cycle Interphase: Period between the end of one mitosis and the beginning of the next.
Steps of Cell Cycle 1. G1 phase (gap 1): cell grows 2. S phase: DNA replicates (copy) 3. G2 phase: more growth 4. Mitosis: Cell divides.
Replication of DNA DNA’s Ability to make an exact copy of itself! Occurs during S- phase of Cell Cycle, before mitosis. Occurs at hundreds of places along DNA strand
Replication of DNA: 1. DNA Unzips: Enzyme Breaks Hydrogen Bonds between nitrogenous base pairs Creates 2 Complementary Strands (templates) 2. DNA Polymerase moves along original strands (templates) Nucleotides come from the cytoplasm DNA Polymerase attaches complimentary bases to both sides of the unzipped strands (Semi-Conservative). 3. Completed: 2 NEW identical strands of DNA are produced DNA Polymerase “proofreads” the new strands
Chromosome Structure Two sister Chromatids Centromere: Holds chromatids together. Chromosome
Chromosomes Found in the nucleus of the cell
Chromosomes Contain DNA Number varies with organism: Humans: 46 Cats: 32 Dogs: 72 Karyotype: shows # of Chromosome pairs
(pause… mitosis is next)
M-Phase: Cell Division 2 Steps: 1. Mitosis: Nucleus divides into 2 nuclei. 2. Cytokinesis: cytoplasm divides to form two new cells. Takes 30 minutes to several hours.
Cell Division
Mitosis Animation
Stages of Mitosis
Interphase: Animal cell: Plant Cells:
2nd: Prophase Mitosis begins (cell begins to divide) Spindle fibers form between the ends (poles) of cell.
3rd: Metaphase Chromosomes line up at the center of the cell or equator Spindle fibers attach to Chromatids, as they prepare to pull them apart
4th: Anaphase Chromatids (or pairs of chromosomes)) separate and begin to move to opposite ends of the cell
5th: Telophase Two new nuclei form Chromosomes appear as chromatin (threads rather than rods) Mitosis ENDS
Cytokinesis Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes