In this lesson, we'll learn the definitions of the cell cycle and of mitosis and go over the different steps involved in each. We'll also take a look at what happens to our cells and our bodies when these processes go wrong.
What Is the Cell Cycle?
Think about your commute to work or school. You probably pass through some traffic lights on the way. If everything is ready, you get the green light to keep moving. If the other traffic still needs time to pass, you have to stop at a red light. You can think of the cell cycle in the same way.
The cell cycle is the series of steps, or phases, in a cell's life. Each cell in your body grows, doubles its DNA, and then divides in two to make more cells as needed. Some cells don't divide often, and it's like they have pulled off the road and parked near the red light. Let's look a little closer at the steps and what changes the traffic lights for a cell.
The cell cycle starts in a phase called G1. In G1, the cell is increasing in size and hanging out, doing its job. Some cells get the stop light here and enter a phase called G0, where they no longer divide, pulling off the road either for some time or permanently, depending on the cell.
Other cells need to duplicate their DNA in S Phase so they can get ready to make two new cells. After S phase comes G2, where the cell makes its final preparations to divide. After G2, the action happens in mitosis, or M phase, where the cell actually divides in two. So cell division is actually only a part of the whole cell cycle.
What Is Mitosis?
Now that we know the phases of the cell cycle, let's look a little at what happens during mitosis.
Mitosis has several stages of its own. Within each stage there are multiple mini-stages, but we'll focus on the big picture for this lesson. The first is prophase, where the coating on the nucleus dissolves and frees the DNA, which has condensed into chromosomes. The spindle fibers, or strings that will help separate the chromosomes, also start to form. In the next step, metaphase, the chromosomes line up at the middle with help from the spindle fibers. After metaphase comes anaphase, in which the spindle fibers start to reel in the chromosomes to either side of the cell like a fishing rod. In telophase, the large cell starts to pinch into two and the nuclei start to come back together. The last stage is cytokinesis where the cells actually split into two.
Cell division in mitosis
Differences Between Cell Cycle and Mitosis
One of the key differences between the cell cycle and mitosis is the length of each process. The cell cycle can extend throughout the cell's entire life depending on how fast it divides. The process could take two to three days in quickly dividing cells, like hair follicles, or may never be completed at all, like in cells that don't divide, like heart muscle or brain tissue. Mitosis, on the other hand, happens quickly because it is only one part of the cell cycle.
There is also a difference in the purpose of each process. Unlike the initial cell cycle, where our cell was growing and doubling everything, during mitosis, the cell divides all that stuff up. The cell cycle makes what we need, and then mitosis portions it out.
DNA amount and structure changes with each cycle as well. For most of the cell cycle, specifically the longest phase of G1, the cell has a normal amount of DNA, which is not condensed into chromosomes. Only during G2, S, and M does the cell have double the DNA. In mitosis, until the cell divides it always has double the DNA. Mitosis doesn't change the amount of DNA in a cell until it splits into two, giving each cell the correct amount. Also, the nucleus that holds the DNA is intact for the entire cell cycle, but breaks down to move the chromosomes around in mitosis.
In summary, the cell cycle is the phases of a cell's life. There are four phases to the cell cycle: G1, where the cell grows; S phase, where DNA is duplicated; G2, where the cell makes final preparations for cell division; and M phase, where the cell enters mitosis. Mitosis, or cell division, is only a small part of the cell cycle. The overall cell cycle lasts much longer, and can actually continue for the entire life of a cell if it enters G0, where the cell no longer divides. But like the cell cycle, mitosis is also divided into stages:
Unlike the cell cycle where everything is duplicated, the point of mitosis is to divide out the materials already created into two new cells. DNA is duplicated during S phase in the cell cycle and remains that way though out mitosis. So in mitosis the DNA is always duplicated, where in the cell cycle it is only duplicated during S and G2.