You started off as one cell: one tiny little zygote containing a full set of DNA (23 pairs of chromosomes). As an adult human being, you are now made up of over 37 trillion cells. This means that that one cell divided to make two cells, each of those cells divided to make 4 cells, those 4 cells divided to make 8 cells and on and on until the 37 trillion cells that make up you today. Even now, your body makes around 60 billion cells each day to create new skin cells, intestine cells, hair cells and and nail cells. When you cut yourself, the body needs to make new cells to heal. And if your cells divide out of control, this can cause cancer and if they stop diving this causes of aging. So understanding how cells divide is super important!
The cell cycle, which is the process of one cell and one set of DNA turing into two cells with two sets of DNA. There are three main parts of the cell cycle:
1. To make two cells from one, you can imagine that a few important things need to happen. First, you need the cell to grow to get bigger and to accumulate enough nutrients to support two cells. Second, you need to replicate the DNA so that when the cell divides, each “daughter” cell gets one copy of the DNA. These two things happen in the interphase part of the cell cycle. Interphase is separated into 3 parts
- Gap 1 (usually just called G1 phase) where the cell grows
- Synthesis (usually just called S phase) where the DNA is copied so that two complete copies of DNA are now in the cell
- Gap 2 (usually just called G2) where the cell grows some more
3. Finally, now that the DNA is separated into the two new cells, these cells have to officially split into two in a process called cytokinesis. You can imagine this is like pulling a drawstring closed to pinch the space between the two cells until they have completely split apart.
If this sounds like a complicated process, you’re right. It is. But it happens flawlessly 10,000 trillion times in a lifetime. Part of the reason why this is a flawless process is because the cell puts checkpoints into the process. It’s like when your bank calls you because they observed a strange transaction on your credit card and they put your card on hold. If the cell sees something strange happening when the cell is trying to undergo cell division, it puts a hold on the whole process until it gets fixed. We’ll discuss this a lot more in the future because when the cell cycle isn’t running flawlessly and these checkpoints aren’t working, this contributes to causing cancer and other diseases.