Batman Likes Equilibrium

               It’s getting on towards Halloween.  Lots of grim reapers, skeletons and one tied up Barbie doll line my trek from the train station to work.  The Barbie doll creeps me out actually – her hands are tied behind her back with duct tape.  That ain’t right.

                Keeping that spirit of death alive, I’m going use this post to explain the following phrase:

A cell at equilibrium is dead.

                What does that mean?  Why is it dead?  Did the Devil come and steal its life?

                In order to understand it, we’ll need to learn a few things.  I’ll try to make it painless.

Thing #1: Batman likes chemistry.

                I’m sure you’ve seen chemical reactions written out as in Figure 40.1.  I’m not going to use real chemicals.  We’re going to keep it simple with A and B.  A and B are related to each other in that they can turn into each other: think of A as Bruce Wayne and B as Batman.  

Pretend we have 100 Bruce Waynes in a room.  All those Bruce Waynes look around and decide there’s way too many of them so some become Batman.  For simplicity’s sake, let’s say 25 Bruce Waynes become Batman.  Now we have 75 Bruce Waynes and 25 Batmans in one room.

25 Batmans / 75 Bruce Waynes = 1 Batman / 3 Bruce Waynes.

            Everyone in the room is happy with this mix of Bruce Waynes and Batmans. 

Let me take a minute and describe this moment when everyone is happy with the ratio.  It is called equilibrium!   The room likes being 75% Bruce Wayne.  However, this does not mean that individuals in the room stop changing back and forth between Bruce Wayne and Batman.  If one guy really wants to become Batman – he’s welcome to! - as long as one Batman then agrees to become Bruce Wayne.  Equilibrium is about the overall numbers.  Individuals within the room are still changing back and forth, but the total number of Bruces Waynes and Batmans are no longer changing.

Oops. We wasted too much talking about equilibrium and now 20 Batmans have left the room. 

           Our room now has 75 Bruce Waynes and only 5 Batmans.  

We established above that the room likes 1 Batman for every 3 Bruce Waynes.  In this new situation, we don’t have enough Batmans.  How do we get more?  

Some more of the Bruce Waynes need to change.

            And so, 15 Bruce Waynes become Batman.

20 Batmans / 60 Bruce Waynes = 1 Batman / 3 Bruce Waynes.

We’re back at equilibrium!

I’m sure you can see that there are many ways we can adjust the above situation. 

Examples:

What if 20 Bruce Waynes left the room? (You’d need more Bruce Waynes!)
What if 200 Bruce Waynes entered the room? (You’d need more Batmans!)

What if you made the room bigger? (They don’t care about the room size, they care about how many Batmans and Bruce Waynes there are.  Duh.)

Whatever you do the room, the overall numbers of Bruce Waynes and Batmans must adjust themselves to fulfill the ratio.

Thing #2: Chemistry likes the Bruce Wayne and Batman Scenario.

                Chemical reactions work like the above example.  To bring it back a little to the real world, consider again the equation in Figure 40.1.

                A will turn into B (and B can turn into A!).  If you put a bunch of A in a test tube, it will start turning into B until enough of B builds up that A says “okay, we’re done.”  The reaction is now at equilibrium.  Remember, individual molecules of A and B will still flip back and forth, but the overall numbers of A and B will no longer change.  

What governs how much B needs to be made before the reaction says enough?  A lot of things.  Suffice it to say that each chemical reaction has its own equilibrium point.  

A reaction is always trying to get to its equilibrium point.  Science, our cells, and life exploit that one fundamental fact mercilessly.

Thing #3: Equilibrium is not for live cells.

                Let’s go back to our test tube example with A turning into B.  Instead of allowing B to build up so the reaction reaches equilibrium, we’re going to continually remove B from the test tube.  Each time A turns into B, we’re going to take out the B.  

                A chemical reaction is always trying to reach equilibrium.  If we keep removing B, A is going to keep turning into B.  It’s going to keep trying to get to equilibrium, but we are foiling its plans.  We are ensuring that A keeps turning into B.

                Why is that useful?  In the Diabetes mellitus post, I told you that glucose is a precious energy source for the body.  The way that energy is extracted is to break down the molecule through a series of steps.  The first step turns glucose into glucose-6-phosphate.  Glucose-6-phosphate is then quickly turned into something else.  

Think of glucose as A and glucose-6-phosphate as B.  B is continually being removed from the reaction because it goes on to be something else.  This means that A will keep turning into B.  A is trying so hard to reach equilibrium with B but it can’t because B keep disappearing.   As long as glucose keeps turning into glucose-6-phosphate and glucose-6-phosphate keeps turning into C, glucose keeps getting broken down and our cells keep getting energy.   

   

What if glucose reaches equilibrium with glucose-6-phosphate?  Overall numbers of glucose becoming glucose-6-phosphate won’t change, which means that glucose is not being broken down efficiently anymore and that our cells are no longer getting energy.  

This pulling of reactions towards B is used in every chemical reaction within our bodies and keeps the reactions happening that keep us alive.

A cell at equilibrium is dead.

REFERENCES

 

Zumdahl, Steven S. “Chemical Principles, 4^th Edition” (2002) Houghton Mifflin Company, Boston, MA.

Alberts et al. “Molecular Biology of the Cell, 4^th Edition.”  Garland Science, New York, New York. (2002).

Me, myself, and I