It’s been a long time in coming, but it’s finally happening: I’m starting my series of introductions to scientific topics that impact our everyday lives. First up is cancer. There is obviously FAR more to say about the subject than I can possibly fit into one post, and if you drill down the biology can get quite complex, but I’m going to do my best to hit the biggest points that people tend to ask questions about, and also to write at a level appropriate for non-scientists. To that end, if you have any questions I fail to answer here OR you don’t fully understand one of my explanations, PLEASE speak up in the comments! I am still learning as a teacher and a writer, and I don’t ever want anyone to assume that a failure to understand what I’m saying means that they aren’t smart enough to get it. Instead, please speak up and give me a shot at a second try!
Before we get started, a few notes:
- I am not a medical doctor and none of what I say here should be taken as medical advice.
- I am also not a cancer researcher and do not know everything there is to know about the state of current research, but I have taken a few graduate-level courses on the subject and I do my best to research thoroughly. If you catch any mistakes, feel free to correct me.
- I was inspired to finally get off my ass and write this series of posts thanks to the episode of the Enquiring Minds podcast that featured George Johnson, writer of the new book The Cancer Chronicles: Unlocking Medicine’s Deepest Mystery. As such, Johnson’s discussion of the topic is fresh in my mind and I may use some of his ideas/wordings in my discussion here. I’d like to thank the podcast and Johnson for the inspiration.
Okay now, with all of that out of the way, let’s get started, shall we? This series will answer the questions:
- What is cancer?
- Why do we get cancer?
- How do we treat it?
…and also do a bit of cancer mythbusting. Today though, we’ll cover topic #1.
What is cancer?
Let’s start at the very, very beginning: with a single cell.
The cell is the smallest unit that can possible considered alive; therefore every living thing on the planet either is a cell or is made of many cells. At it’s most basic, a cell is made up of a handful of things:
- Some kind of divider between the cell and the outside world. In most cells, this is just a membrane–a layer of lipid molecules*–but some get all fancy about it and make walls around their membranes out of proteins and/or sugar polymers**.
- A genome–DNA that encodes all the information necessary to build the cell. Genomes include genes, which we generally think of as coding for proteins. Proteins do most of the work of the cell–transporting substances in and out, “reading” the genetic code, replicating the DNA, etc.
- Ribosomes, which are basically little protein factories. These do the job of turning that genetic code from the genome into proteins.
- A bunch of proteins running around doing all the jobs needed to keep the cell alive and growing.
Some cells are more complicated and have what we call organelles, which are basically little membrane-enclosed areas that perform specific jobs for the cell. But for now, let’s not worry about the complexity of the machinery.
The big picture is this: a single cell living alone is a little sac of chemicals that exists to collect materials and energy from the environment that it can then use to sustain it’s basic housekeeping activities, grow, and produce little copies of itself. There is, of course, a finite number of such resources available, so cells end up in competition with one another, fighting a constant arms race to collect nutrients more efficiently, to grow faster, to divide faster. Every man for himself.
Constant competition between individual cells, is, as it turns out, only one way to go about this whole living thing. Over the course of evolutionary history, many single-celled organisms developed varying levels of interdependence. In a very simple example, a clump of bacteria may have the ones towards the outside specialize in obtaining food, and the ones towards the inside specialize in making complex biochemicals that provide some competitive advantage by, say, killing off other nearby species, or helping the clump of bacteria stick to a safe and cozy surface. For some species, this strategy of living communally and cooperatively was so effective, that the system of specialization and cooperation became ever more intricate and permanent, eventually leading to the development of multicellular organisms.
There are undoubtedly major advantages to this strategy–the degree of specialization possible when a group of cells is tied together permanently, thus becoming entirely dependent on one another for survival and reproduction, is almost endless (I, for one, am a big fan of nervous systems–consciousness, woo hoo!). But like any strategy, it has its costs. Even the most basic level of cooperation between single-celled critters requires some rudimentary communication abilities–the cells must be able to produce and respond to chemical signals that say things like “I’m here!” or “plenty of food coming in, you builder cells keep on building!” or “crap, we’re running out of space!”
Additionally, specializing requires that individual cells control their activities in ways they wouldn’t necessarily have to if they lived alone–for instance, turning off their “grow and divide” program in order to shift resources into the “build chemical weapons against competitor X” module. And the system needs to be pretty damn effective–after all, if you’re scaling back your food-harvesting efforts in order to produce weapons for the community, the other members of the community damn well better have your back, or you’ll starve pretty quickly.
Multicellularity requires incredibly complex systems of communication and control. In complex multicellular organisms, a significant number of mechanisms exist to exert this control over every individual cell in the body. And this control is powerful: a very commonly used mechanism in growth, development, and maintenance of multicellular organisms is apoptosis, or programmed cell DEATH. Cells can be told to die because they are infected with a virus, because they aren’t needed anymore (for awhile in the womb, all of us have webbed fingers and toes… until all the cells in the webbing are told “hey you! time to die!”), because they are acting strangely and present possible danger… pretty much anything.
Remember, left to their own devices, individual cells want to eat, grow, and divide endlessly, but the evolved mechanisms of control are so strong that our cells regularly kill themselves for the good of the body as a whole. This same control makes brain cells stay brain cells and muscle cells stay muscle cells and so on and so forth as required to keep the entire complex machine running smoothly. It’s a beautiful, intricate system that medical science is still working to understand in greater depth, but the bottom line is that it works, somehow, to keep all our parts doing their respective jobs.
Until, of course, the controls fail.
If all of your growth-control mechanisms run smoothly, you’re golden. If one or two break in a given cell, you might still be fine–evolution is ‘smart’ enough, in its way, to have built in a significant amount of redundancy. The real problem begins when enough of the mechanisms break in one cell that it stops acting like a well-behaved skin cell or muscle cell or immune system cell, and starts acting more like a selfish free-agent. When that happens, when a single cell reaches the point of having so little regard for its place in the world that it goes rogue… we call that cancer.
Tomorrow, I’ll get into WHY these growth-control mechanisms fail. Stay tuned!
*lipids are molecules consisting of mostly carbon and hydrogen that we know as oils and fats. Whether any given lipid is referred to as an oil or a fat is dependent on whether they are liquid or solid at room temperature, which depends on the structure of the bonds between the carbons.
**polymers are molecules made up of long chains of smaller molecular subunits, which are often referred to as monomers. Most important biological molecules are polymers–DNA is a polymer made up of monomers called nucleotides, proteins are polymers made up of monomers called amino acids, and simple sugars can be connected together in a variety of ways to create polymers called polysaccharides that can be used for storing energy (for example: starch in plants, and glycogen in humans are both storage polysaccharides) or for structural material (the tough cell walls of plant cells are made of a polysaccharide called cellulose).