To understand physiology, you have to understand cells. To understand cells, you’ve got to understand DNA and self-replication. And you can’t understand DNA unless you put them in the context of chemistry and physics …
Atoms are the building blocks of nature. They are mostly empty space: a tiny clump of protons and neutrons, like a baseball floating in the centre of a stadium, plus some electrons whizzing around the stands like peanuts.
What gives it substance, then? Only the weird, extreme, and arbitrary forces of the universe hold it together. Like magic, you simply can’t wedge anything else between the electrons and the nucleus — and so they seem solid.
Add a single proton to an atom, you get a different kind of atom. If you add too many, they don’t hold together well, and the structure is radioactive, and sheds subatomic particles and energy that can disrupt other matter. There are several dozen kinds of more or less stable atoms, each one of them called an element, like iron, magnesium, or carbon.
This is atomic physics.
Combinations of elements — several atoms stuck together — are molecules. Atoms and molecules combine in almost infinite ways, making up everything in the universe. For all the variety of combinations, however, only one element — carbon — combines into impressively complex molecules. These super molecules are the basic ingredient of life. This is why we are a “carbon-based” life form. Silicon is the only other element that could, conceivably, combine to create molecules complex enough for life: but here on Earth, carbon is the king.
This is chemistry.
Somehow — and this is one the great mysteries of biology — organic chemistry got too big for its britches. The king of the carbon-based super molecules is deoxyribonucleic acid, or DNA. This molecule is special because it has the somewhat spooky ability to make copies of itself, a process as lifeless in itself as any other chemical reaction — just unusually complicated chemistry. This ability to self-replicate had some extraordinary consequences, starting with natural selection and leading to the dinosaurs, you, Elvis, and this book. How?
Naturally, DNA’s talent for cloning itself resulted in a whole bunch of DNA molecules kicking around. At the dawn of life, slight errors and differences in all that copying — caused by the interference of radioactivity — resulted in some DNA molecules that were better or worse at copying themselves. It doesn’t matter how many of these detours were impotent, as long as any of them worked better. The ones that were better at it became more numerous, and evolution was born.This ability to self-replicate had some extraordinary consequences …
In this way, over hundreds of millions of years, by slow and random accumulation of slightly more effective methods of self-replication, DNA molecules gradually developed complex chemical machinery for aiding and abetting the process of replication. And somewhere in there, during some uncelebrated stretch of eons, that chemical machinery became so elaborate that it crossed a vague gray zone and became … alive! Cells were born.
This is biology.
Although the articles in the Biological Literacy series can be read in any order, here’s a logical next step: We Are Full of Critters: The human body is a colony of ten trillion co-operating cells