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Cells replicate by splitting in two through a process called mitosis, which partitions roughly equal amounts of their contents into each new cell. The cell's genetic material, DNA, is contained in a ball-like compartment called the nucleus. The cell only has one nucleus, and it can't just be hacked into two equal parts for the new cells.
Thus, before the cell can split, it must create two copies of its genetic information. Here's how it works:
Step 1 - Prophase - DNA condenses from a loose coil into several pairs of chromosomes. Structures called centrioles move to opposite ends of the cell.
Step 2 - Prometaphase - The nucleus' membrane begins to break up. Protein "ropes" called microtubules attach to the centers of each chromosome and to each centriole.
Step 3 - Metaphase - Chromosome pairs are split and each chromosome, each of which looks like an "X", is lined up along the center of the cell.
Step 4 - Anaphase - The centrioles begin reeling in the microtubules. This splits each chromosome in half--like pulling on a wishbone--and one leg, called a chromatid, from each "X" is pulled to each end of the cell. This ensures that each new cell will have one half of each chromosome in the original pair.
Step 5 - Telophase - As the chromatids near the cell's poles, new nuclear membranes form around the material. The chromatids revert to their loose state and the microtubules and centrioles disperse.
After telophase, and sometimes during the final stages of it, the a fibrous "belt" begins to tighten around the middle of the cell, cinching and pinching off two nearly equal-sized daughter cells, each with their own nucleus.
The image above shows groups of boxy cells undergoing various stages of mitosis. The artwork, which was created bye superimposing images on a mass-produced floral fabric, won first prize in Princeton University's 2006 Art of Science competition.
Amazing Images: Science & Nature Photos from Our Readers
Credit: Jennifer Rea/Princeton U. 2006 Art of Science Competition
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