Cells: 1. Membranes: separate cells from the outside environment 2. Ribosomes: make proteins 3. Mitochondria: “powerhouses” where ATP is produced 4. Nucleus: stores chromosomes 5. Nucleolus: area in the nucleus where ribosomes are made 6. Centrioles: structures to which spindle fibers attach DNA: 1. Nucleotides 1. Adenine 2. Guanine 3. Thymine 4. Cytosine 1. Contains 3 billion nucleotides 2. Bundled in structures called chromosomes 3. 2 strands held together with hydrogen bonds (double helix) 4. 46 total chromosomes in each cell (23 from mother, 23 from father) Mitosis (cell division): 1. Prophase 1. Spindle fibers form and attach to centromeres of each pair of sister chromatids 2. Nuclear envelope dissolves and centrioles move towards opposite ends of the cell 3. Kinetochore connects the spindle fibers to the centromeres 1. Metaphase 1. Spindle fibers pull the chromosomes to the center of the cell 1. Anaphase 1. Sister chromatids are pulled apart and pulled to opposite ends of the cell 1. Telophase 1. The cell divides in half 2. Spindle fibers disappear and a nuclear envelope forms around each set of chromosomes