Red light green light: Hypoxia says go!
Take a deep breath. We’re about to talk about how that oxygen you're breathing in can turn into deadly chemicals.
If you’ve been unfortunate enough to learn the TCA/Krebs/whatever they’re calling it now cycle, you may already know some of what we’re about to tell you. The TCA cycle (that’s how I learned it and that’s what I’m sticking with) is a pathway that breaks down the sugars in your food into smaller molecules that will feed into the electron transport chain. The ETC then takes the electrons and transports them to different proteins, eventually generating ATP as energy for your cell (that’s the grossly oversimplified version- you’re welcome).
During this process, electrons are transiently grabbed by molecules, including the oxygen you breath in, creating what is called a radical. These oxygen radicals are very reactive on their own. Even worse, they can turn into non-radical species (e.g hydrogen peroxide) that still cause damage to molecules. These species that derive from and include oxygen radicals are dubbed “Reactive Oxygen Species”, or ROS. Under healthy conditions, your cells produce low levels of ROS. Most of these can be immediately soaked up by proteins and are sometimes even used in biological processes. The issue comes when you have TOO much ROS, and they overwhelm a cell’s natural ability to clear these molecules. The ROS will then begin damaging your cell by attacking other molecules such as your DNA, proteins, or lipids.
Let’s go back to those hypoxic cells at the center of tumors that we learned about from our talk with Ines. Under hypoxic conditions, the production of ROS can significantly increase (it’s a complicated process, but take our word for it). Our very important DNA and protein molecules nearby become susceptible to mutation and damage. Some of these changes can make a cancerous cell even more dangerous by promoting entry into the bloodstream (where it could metastasize). However, most cells cannot readily survive in the bloodstream. Fortunate for the hypoxic cancer cells, their ROS-filled environment triggers them to express a variety of proteins that help them deal with hypoxia and the harsh bloodstream. So, while ROS and hypoxia are usually really damaging to healthy cells, such harsh conditions surprisingly help cancer cells to metastasize.