Friday, May 14, 2010

Connection between Glucose and Energy


The question was purposed on how would your explain the connection between glucose entering the body and energy created by the body to a friend, using your new biochemistry knowledge? 
Original picture by J. Russell 2010

Glucose enters the body. I start explaining the process and my friends leave the room.  Just kidding.  It is a story involving the major component of most of our snack foods, my friend's and I enjoy.  Glucose is a major source of energy for the body. It can be used for energy to running cell processes by the metabolizing of the glucose. The breakdown or catabolism of glucose converts this source of energy to adenosine triphosphate or ATP.  Pause for dramatic effect.  Oh, but it is not done so in one easy step. The high point is glucose is no slacker when it comes to producing the body's energy currency source.  It yields 36 ATP molecules which is an average of 6 ATP per carbon atom.  Not a bad rate of exchange. This conversion from food source to energy source is accomplished by the powerhouse of the cell called the mitochondria. The process that links catabolism to ATP consists of intermediate steps of the citric acid cycle (TCA), electron transport chain and oxidative phosphorylation. Now if my friends, if they have not left the room, want the basic details of what those consist of here it comes.  TCA packs a punch to break down that glucose and put it to work with eight reactions utilizing eight different enzymes: citrate synthase, aconitase, isocitrate dehydrogenase, succinyl-CoA synthetaase, sucinate dehydrogenase, fumarase, and malate dehydrogenase. Painting with broad strokes, the catabolism of glucose produces acetyl-CoA that is then input into the TCA which through the cascade of eight reactions then produces oxaloacetate (oxidation of acetyl group), two NADH molecules, a GTP molecule, a FADH2 molecule and two CO2. Oxidative phosphorylation utilizes the electron transport chain to convert the TCA products.  Pause again to let my friends refocus for the big finale.  The electron transport chain consists of four protein complexes: complex I oxidation of NADH, complex II oxidation of FADH2, complex III oxidation of COQ and complex IV oxidation of cytochrome C.  Interestingly, the product of the electron transfer chain is energy and water.  But wait my friends say, "You said the energy currency of the body was ATP.  Now you are rewritting the ending."  Wait for it.  This free energy is utilized by ATP synthase to produce ATP from ADP and inorganic phosphate within the mitochondrial matrix.  Remember the powerhouse of the cell I interject.  Finally, the ATP is released by the mitochondria to the cell to be used as energy for body processes.  Pass the chips and dip my friends say.  They need to fuel up on some ATP.    Now we are talking lactate and starch, but that is a story for another day.

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