Tuesday, March 06, 2007

White and Dark Meat

I came across a blog Omics! Omics! today and read a blog entry containing this interesting tidbit.

"First though, we need to review some biochemistry. The metabolism of sugar to energy in our cells requires a complex pathway of events. The system can be divided into three basic subsystems: glycolysis, the citric acid (or Krebs) cycle, and the respiratory electron transport chain. The handoff from glycolysis to the citric acid cycle is the molecule pyruvate. However, this three stage system requires oxygen; in the absence of oxygen energy production halts at glycolysis. Which means the cell needs to deal with all that pyruvate, or the system stalls.

The first biotechnologists discovered that yeast has a very interesting solution to this problem: it converts the pyruvate to ethanol. But in animals, the endpoint is instead lactic acid. It is lactic acid buildup that gives you a burning sensation from tired muscles. Obtaining energy solely from glycolysis is far less effective than going the whole scheme (about 6X if I remember correctly), so animals tend to reserve it for special occasions -- such as quick bursts of muscle activity or other occasions when oxygen can't get to the cells fast enough. As my freshman bio prof pointed out, this leads to the white meat vs. dark meat dichotomy of chickens: chickens walk all the time, so the legs operate in the aerobic regime, whereas the wings are for short flights and operate anerobically. The oxygen storage protein myoglobin contains oxygen & gives the dark meat its characteristic color."

It works for turkeys too; a favorite of mine. BTW, oxygen can be toxic to organisms lacking enzymes that prevent destructive effects this element can engender. Aerobic glycolysis requires oxygen and anaerobic glycolysis can occur without it. Pyruvate is the end product of aerobic glycolysis. Pyruvate is then converted in another pathway- the tricarboxylic acid cycle.



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