Q How are cells created?
— Becca Lynn, home school
A Beth Weaver, associate professor in the department of cell and regenerative biology and the department of oncology at the University of Wisconsin-Madison:
New cells are created from existing cells through a process called the cell cycle. One cell can make a copy of itself and form two new daughter cells.
There are two major tasks that must happen every cell cycle. First, cells need to make an exact copy of their DNA. DNA is like the instruction manual for a cell. It encodes genes for characteristics and dictates things like eye color and blood type.
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DNA is organized into chromosomes. Most bacteria have one circular chromosome, while animal cells, including human cells, have multiple linear chromosomes. These chromosomes get replicated during the synthesis phase, or S phase, of the cell cycle.
The second major task of every cell cycle is for the replicated chromosomes to be organized and separated into opposite sides of the cell. This happens during mitosis, or the M phase of the cell cycle.
During mitosis, cells build a molecular machine, which is known as the mitotic spindle. The mitotic spindle is composed of filaments, called microtubules, that grow and shrink. The microtubules connect to the chromosomes and organize them in such a way that they all line up in the middle of the cell.
After the chromosomes line up in the middle of the cell, they then separate to opposite sides, still connected to the microtubules.
The cell then grows longer, further separating those masses of chromosomes. The middle of the cell then pinches off in a process known as cytokinesis, splitting the cell into two cells. A new cell has been created, and that completes the cell cycle.