Re: Does the nucleus in a cell control it like our brain controls our body?

Thank you for your interesting question.

In a way of speaking, the nucleus can be conceived to be the “brain” of the cell, but you have to remember that you cannot take a literal translation of this metaphor. When we think of the brain we think of an organ capable of thought, and calculation, which makes judgments. Based on these judgments, the brain then directs the body to react in some way. Of course, the brain can also work on a much more primitive pathway – namely the reflex arc. As you will see, the nucleus doesn’t really do a whole lot other than act as a container for the DNA, and the DNA doesn’t do as much in and of itself – but the proteins it codes mean the whole world!

So, let’s consider things a little deeper. A cell reacts to its environment, as does the human body. The cell contains on it various kinds of receptors, which transmit information from the environment to the cell for processing. These receptors can pick up all kinds of signals, like steroids, glucose, heat, and others. The body does something very similar, using our five senses we are able to “pick up” environmental signals, too. The sense organs of the body then transmit their information to the brain, where the information is processed, judgments are made, and some reaction takes place (even a lack of a response is a response).

The cell, as I have already said, takes up a signal. The receptor processes this signal, and reacts accordingly within the cell. Depending on the kind of receptor, and what the signal is, something can happen in the long-term, or short-term. Long-term reactions are usually mediated by some mechanism within the nucleus. The short-term reactions are usually handled by the proteins without needing to confer with the DNA. A short term mechanism you might be familiar with would be something like a Na+/K+ pump.

Now let’s look at the nucleus. The nucleus does not contain within it any ability to think. Nothing in the cell contains that ability. Instead, the nucleus just contains the DNA (some RNA as well). The DNA encodes every possible protein that the cell can make. Now here’s the interesting part – those receptors that I talked about before, and the signals that they pick up – those can actually regulate what proteins are made (this is called regulation of gene expression). In other words, those receptors have control over the DNA. Although the DNA is important, and without it the cell would not exist, I would not use the analogy of the nucleus being the brain. It’s not that one shouldn’t use that analogy, it’s probably a very appropriate one for pre-college studies. Everyone is familiar with the importance of the brain – and that is probably where the analogy could be drawn – the nucleus is essential for the cell, just as our brain is essential for us (there is no “brain” machine at the hospital to help keep you thinking, although that would be pretty cool wouldn’t it? Increase your brain power through the use of a machine that you just plug in to!).

To answer your questions further, I’ll describe a bit of how the brain works, and how cells work. The brain has many different ways in which it can control various parts of the body. One way is by sending electrical messages down the spinal cord to various parts, and using chemical cues which interact with other neurons at the target, causing some kind of change in the cells. That’s more or less how the CNS (central nervous system) works. An excellent example would be muscle twitches. The brain sends a signal down the spinal cord, to let’s say a leg muscle. There is a neuron from the spinal cord that interacts with a muscle cell. The neuron secretes a chemical (in this case acetylcholine), which binds to a receptor at the muscle cell. This causes an electrical signal to be started in the muscle, and various things take place, leading to the muscle contracting. The muscle then relaxes. And presto – you’ve experienced a muscle twitch!

Another mechanism that the brain can use to direct the body is by the use of hormones. A prime example here is the secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus (a structure in the brain). GnRH then meets its receptors in the pituitary, and causes the pituitary to secrete luteinizing hormone (LH) and follicle stimulating hormone (FSH). Those hormones then travel to the testes or the ovaries, and have different actions depending on which organ they end up at.

The nucleus doesn’t do either of those things. The nucleus just sort of hangs out, and protects the DNA, as well as some RNA. When a signal comes in via a receptor, the cell responds. One kind of signal is that acetylcholine in the case of the skeletal muscle. The acetylcholine binds to the acetylcholine receptor, and causes an ion channel to open up, which allows ions to pass into the cell. Then the muscle shortens. In this case, there is no gene expression going on. However, in the case of the LH, it binds to its receptor on the ovary (or testis, but I’ll talk about ovary in more depth, since I’m more familiar with this system), the receptor activates several different proteins, which leads to the activation of a DNA binding protein. This DNA binding protein then stimulates the expression of various genes.

I hope that answers your questions. I hope I didn’t overwhelm you with more information than you wanted to know :0)

Thanks again!