With 37 trillion cells in our bodies, the idea of keeping everything the same, high quality, sounds like a nightmare. Luckily, we don’t have to actively check each cell and make sure it’s doing everything right; they do it themselves. Every single one of those 37 trillion cells is constantly performing quality control checks to make sure we keep running properly. There are a lot of different aspects of a cell that we want to make sure are working properly. Our cells ensure their mitochondria are functioning properly, organelles that provide cells with their energy. They constantly check their DNA to ensure their instruction manual has no mistakes. And, critically, our cells are constantly checking to make sure that they only divide when they’re supposed to.

All of these are critical parts of a cell that, when damaged, need to be repaired for a cell to live. If cell division is left unchecked, it can lead to several serious diseases, one of which is, of course, cancer. Luckily for us, our cells are equipped with rules, instructions, and ways to defend us if cell division goes wrong. These are called tumour suppressors, and they keep cancer at bay.

Cell division is absolutely critical to being a functioning human. In fact, it’s critical to almost all multicellular organisms. Without cell division, we’d all just be single cells floating around — basically just bacteria. There are many different reasons that cells divide, starting all the way back at our conception. As an egg is fertilized, cells start to divide, and cell division is exponential. That means that one cell becomes two, then each of those two cells divides to become four, and so on.

For growing embryos, this is really important. Starting from just a single cell, an embryo needs to grow, ultimately becoming a tiny little human. But cells don’t just divide for the purpose of growing in size. For example, the lining of our gut is constantly dividing. Our gut is constantly exposed to acid from our stomach and anything potentially harmful that we’ve eaten. This exposure can damage or even kill cells lining our gut, so cells in this area rapidly divide, constantly replacing the old, damaged ones. Our bodies actually clean up and replace around 330 billion cells every single day. With so many cells dividing, and with division doubling the number of cells so quickly, we can hopefully see how quickly things could get out of hand if our cells didn’t do their quality control.

A tumour suppressor is a gene that controls cell division, repairs DNA damage, or gets rid of faulty cells, and they’re essential to protect from cancer. They’re responsible for checking to see if all aspects of cell division are as they should be, and if not, they step in and put a stop to it.

There are a few different ways that tumour suppressors help regulate cell division. The first is by simply stopping before we start. A cell only divides when it has enough space and nutrients. It needs all the building blocks to double in size. If the cell is low on nutrients, certain tumour suppressors will essentially block any chance of even starting division. Because of checks like this, a cell only starts dividing when all of the conditions are right. Then, and only then, will a cell start using those building blocks to replicate its DNA and all of its other bits and bobs.

But what if a cell has already started dividing and something goes wrong? Fortunately for us, our cells have got that covered. There are a lot of things that can go wrong during cell division, like having its DNA damaged. If something goes wrong during cell division, tumour suppressors can intervene. Some tumour suppressors can essentially pause division to give the cell a chance to fix any problems. If the damage is too severe, some genes can cause a cell to go through apoptosis. Apoptosis is a form of programmed cell death that occurs when something goes wrong. That’s right, our cells are so committed to quality control that they would rather die off than risk developing into a disease.

Despite all the chaos of cell division, tumour suppressors make sure everything is perfect, or that the cell stops dividing, or is thrown away.

As our DNA is damaged, we can lose critical information, rules or instructions that are critical to proper cell division. If a cell's DNA is damaged right in the middle of a tumour suppressor gene, it can lose the ability to self-regulate. Having its DNA damaged in a specific tumour suppressor gene can lead to the loss of some of our critical checks and balances. Some mutations might cause a cell to continue dividing even when it’s not safe to do so. Some DNA damage might cause a cell to divide even though it doesn’t have enough space. Some damage can even cause a cell to lose its ability to repair DNA, leading to more DNA damage. As damage accumulates, the cells’ quality control drops, and the risk of cancer rises.

Fortunately, it’s exceptionally rare for a cancer to be caused by a single case of DNA damage. A cell usually has to undergo several mutations to become a full-blown cancer cell. And, with 37 trillion cells, it’s exceptionally rare that the exact same cell will be damaged in the exact right genes, all at the exact same time.

The idea of keeping 37 trillion cells working properly sounds like a nightmare. With constant exposure to carcinogens, elements that can damage our DNA, it only gets harder. And as we’re exposed to more and more carcinogens, cancer grows. Fortunately, our cells keep doing everything they can to keep that from happening. Although dividing is a chaotic and demanding process, we have our tumour suppressors keep things running smoothly. Each one keeps an eye out for flaws or faults in a cell’s division, and if they notice anything, they quickly intervene. We even have backups, so that if we lose one tumour suppressor, another can take its place. Our tumour suppressors are so effective that they’d rather a cell die off than become a disease, because that’s the safer option. Thanks to tumour suppressors and all our different checks and balances, our cells can keep dividing safely, producing only the finest quality.

I hope you learned a little something today, but next week we’re talking about a new way to deliver drugs straight to cancer - nanogels.

See you next week!

If you missed last week’s letter, you can read “That’s The Dream” to learn about the role of sleep in cancer… and the role of cancer in sleep!