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The Life Cycle of a Cell
The Life Cycle of a Cell
Cells are living things, of course, so it is appropriate that we refer their lifespan and activities as a cell's life cycle. Cells involve many different signals, chemical reactions, and more depending on the cell's jobs, of course. But, there is a general life cycle that applies to most cells that is nice and general. That life cycle is shown here.
As you can see, the cell's life cycle is typically represented in a circle (because it is a cycle) that renews when the cell reproduces...but more on that later.
Let's focus for now on just the 2 major phases:
Interphase
Mitotic Phase
Interphase, as shown in grey in the outer circle, comprises the vast majority of the cell's life. The mitotic phase, shown in the peach color, makes up just a small sliver of time in a cell's life. Let's zoom in on each of these phases a bit more.
Interphase: The Vast Majority of a Cell's Life
Interphase: The Vast Majority of a Cell's Life
As mentioned previously, interphase is the phase of life in which cells spend the vast majority of their lives. If a cell is functioning normally and doing its job, it is almost certainly in interphase. The only time cells leave interphase is when they are reproducing. As you can see in the diagram, interphase is made up of 3 sub-phases: the G1, S, and G2 phases. In reality, there is an unusual fourth phase known as the G0 phase, but we get to ignore that phase for our course! Let's talk about each of these phases individually:
G1 Phase - All About Growth
G1 Phase - All About Growth
During the G1 phase, the cell will start duplicating its organelles and other cellular components. This is the start of the preparations for mitosis, or cell division. The cell is eventually (during the mitotic phase) going to split into two cells, so it is going to have to grow larger and start to duplicate some important enzymes and other cellular components.
S Phase - All About Synthesis
S Phase - All About Synthesis
Just like in the previous phase, this phase will ultimately help to prepare for cell division as well. This time, however, the cell will duplicate its DNA - copying every chromosome so that there are copies of each to go into each daughter cell. The S standards for 'synthesis' because the cell is synthesizing, or building, new copies of DNA.
G2 Phase - Better Double-Check!
G2 Phase - Better Double-Check!
During this phase, the cell will be growing larger...again... and doubling more cellular components such as organelles. Now that the cell has doubled everything... hopefully... so you might be thinking that it is time to divide into two cells. Well, not quite. For reasons that will become apparent when we discuss mitosis in more depth, it is VERY important that cells be absolutely sure that everything is in order before they divide. Otherwise, some very serious issues will arise. So, this phase also includes checking to make sure that everything doubled properly before moving on to the mitotic phase of the cell cycle. In reality, some more growth of the cell occurs here too, but don't worry too much about that for this course.
Checkpoints Between These Phases
Checkpoints Between These Phases
These phases are all, in reality, separated by different 'checkpoints', or times in which the cell will check to make sure everything is in order before proceeding to the next phase. These checkpoints are crucial, and were mentioned at the end of the G2 phase, but you do not need to memorize specifically what occurs in any checkpoint.
Mitosis: A Small Portion, But Gets All the Glory
Mitosis: A Small Portion, But Gets All the Glory
Mitosis is the most exciting part of the cell cycle, admittedly. This is when the cell finally splits into two identical daughter cells, but I will cover that phase (and its sub-phases) on a separate page.
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