Mitosis and the cell cycle
The cell cycle and mitosis
Body cells divide in a repeating so an organism can grow, repair damaged tissue, and replace worn-out cells. Most of the cycle is , when the cell grows, carries out normal functions, and copies its DNA and organelles.
The nucleus of a human body cell contains , arranged in 23 pairs. When the DNA is copied, each chromosome becomes two identical copies, ready to be shared between the two new cells.
During , the copied chromosomes line up and are pulled apart so each new nucleus gets an identical set. The cytoplasm and cell membrane then divide, producing two new cells that are genetically identical to the parent cell and to each other. In humans, each new cell has the full 46 chromosomes.
Key terms
How bacteria divide differently
Bacteria are prokaryotic cells, and they don't use mitosis — they divide by . This differs from mitosis in three main ways:
- : bacteria have one circular chromosome plus small rings of extra DNA called , instead of DNA held in a nucleus with multiple chromosomes.
- Process: the bacterium copies its chromosome and plasmids, then splits in two directly — there are no equivalent phases to mitosis's chromosome alignment and separation.
- Size and speed: bacterial cells are far smaller than eukaryotic cells (roughly 1,000 times less volume) and can divide roughly every 20 minutes under ideal conditions, much faster than a eukaryotic cell cycle.