Ever since middle school when students learn about cells, they are taught that nucleus is the control center of the cell. They hear that the nucleus is “the brain” and in charge of all cell functions. When teachers do the cell-as-a-factory analogy, the nucleus ends up being the boss. This is not technically true… while the nucleus houses all the information the cell needs to complete different tasks, it isn’t in charge of when that information is used. We need to make sure students understand why cells do the things they do, and it all comes down to cell signaling.
Cells complete cellular processes when the cell membrane gets a signal from the outside environment. Once the signal is received, then the cell will respond by using the genetic information in the nucleus to carry out the task. That task will generally keep going until the signal is terminated. Here are a few examples:
- When red blood cell levels are low, the kidneys release a hormone that signals and stimulates the bone marrow to produce more blood cells.
- When your stomach is empty, it absorbs a hormone called Ghrelin, which signals brain cells that you are hungry. When the stomach stretches after eating, hormone absorption stops.
- When something goes wrong in a cell or it grows too old, a stimulus will activate a protein called caspase, which causes cell death (apoptosis).
You see, the only way a protein or gene knows what to do, is because an environmental signal sent a message to the cell. The gene did not self-activate.
How to get students thinking:
This can be a tricky concept to introduce to students. High school students don’t usually understand how the cell operates as a whole and communicates with the outside environment. A great way to introduce the topic is by posing them these questions: “Are identical twins truly identical? Is it possible for one twin to get cancer while the other does not get cancer?” Most students will say yes, this is possible. But if they have the same genes, how can this be? Our cells are not pre-programed to behave based on our DNA. Genes are only regulated based on signals from the environment. Many students also get confused when we talk about “the environment,” because they are so used to hearing this term used in ecology. Make sure students understand that the cell has its own environment within the body.
The moral of the story:
- Teach students that the nucleus is an organelle that contains DNA inside.
- The nucleus is not in charge of cell activities. (If this were the case, every disorder you are predisposed to have would be manifest. We know this is not the case).
- Cells do things because they respond to signals from their environment, many of which come from the cell membrane.