Energy Flow and Enzymes - Shmoop Introduction

Mark Twain once said, "And what is man without energy? Nothing—nothing at all." A cell's ability to use energy to create order in a universe that is always headed toward disorder is a defining aspect of life. Without the ability to extract and use energy, we would indeed be "nothing—nothing at all." Logically, therefore, we need to discuss energy in the context of biology fairly early on. And by fairly early on, we mean now.

Physics and Chemistry can be thought of as the parents of Biology, setting the rules and regulations that govern every biological process and structure. But, unlike the rules set by your folks, the basic fundamental laws of physics cannot be broken. There are two major laws of physics that are extremely important in biology: the first and second laws of thermodynamics.

• The first law of thermodynamics says that energy can be changed from one form to another, but energy can never be created or destroyed. That's a pretty big "but," if you ask us.
   
• The second law of thermodynamics states that the amount of disorder in the universe is always increasing.

Trippy. What does it mean when we say that the amount of disorder in the universe is always increasing? This law might seem a little strange at first glance because our society looks like it is becoming more organized, not less. There are more roads to build, more buildings to erect, more rules to follow, and more social networks to join. Apple comes out with a more organized, more expensive (albeit awesome) iPhone every year. Your body is also an excellent example of organization, efficiency, and function.

In fact, the only things you may be able to think of that are barreling toward a disordered state faster than you can blink are your bedroom floor, school locker, and Gmail inbox. Let's face it: keeping up with all of Life’s expectations can be…challenging. What would we all do without our iPads and Xbox Kinects to distract us? (Come on, we all know that you, too, have a weakness for Dance Central. Disco fever!)

While it may seem that every cell in your body is a little Houdini that somehow defies the laws of physics, there is actually no magic involved. The reason is that the second law of thermodynamics applies to a contained, whole system: the universe. Therefore, while a cell is extremely ordered, the universe as a whole is heading toward a more disordered state.

When it comes to applying these fundamental laws of physics to biology, though, it is helpful to know about another physics term called free energy. You could think of free energy as a parent that gives you his or her credit card to pay for gas, but free energy is a little more complicated than that. Free energy is the amount of useful energy that can be extracted from a reaction.

Importantly, if a reaction has negative free energy, this means that the reaction will occur… sometime. Sometime? OK, maybe knowing that something will occur sometime in the future isn’t terribly useful. Can you imagine if your folks told you that they would let you use the car sometime over summer break? How are you supposed to plan to gather your fellow homefries and drive them to that Bruno Mars concert in August? Thanks a lot, Mom.

That’s where enzymes come in. Enzymes are in many ways the fast-forward buttons of biology; they "fast-forward" biological reactions so that they occur on a timescale compatible with Life.

You may not be that psyched about seeing physics content in the biology section, but believe us when we say that a foundation in physics will give us much more insight into biological processes and structures. In fact, looking at cells from a physics perspective can help answer some of the most difficult questions in biology, like the "why" questions:

Why do biological reactions happen so quickly?
 
Why does a cell membrane look the way it does?
 
Why does a certain type of protein take on a floppy, loop structure?
 
Why aren't I out watching a movie right now?

OK, maybe it won't answer that last one. But, if answering the other three questions doesn’t make physics just a little bit cooler, we don’t know what does. (No offense, Physics.)