De-Nature of Proteins

We've talked about what meat is made of - muscle (apologies to any vegetarians reading this!). But what happens when you cook meat? Why does it look and taste so different?

Meat is mostly made up of water, fat, and proteins, which are very long molecules composed of building blocks called amino acids. You can think of a protein like a necklace, with the amino acids being the individual beads. Normally, these protein necklaces are coiled up in a very specific shape. But when they are heated, this shape falls apart, and they just become shapeless blobs - this process is called denaturation. Imagine a rope tied in a very complicated knot that somehow becomes untied and end up just as a pile of rope. When you cook meat, you denature the proteins, which has several effects:

• Denatured proteins are easier for our stomachs to digest
• Denatured proteins make meat firmer and not so slimy
• Denaturation disrupts the stringy muscle fibers, making the meat easier to chew
• Denaturation changes the color of meat from translucent to opaque

Cooking has other benefits, as well, since it kills bacteria and improves flavor. However, those aren't related to the denaturation process. So, how do you like your meat cooked - rare, or well-denatured??

Mighty Muscles

Let's talk some more about how muscles work, whether they're in a turkey leg or in your arm.

Make a muscle with your upper arm like the yellow guy at right is doing. Place your other hand on top of the bulging muscle (called the bicep) and straighten your arm. Can you feel something moving? What's really going on in there?

Muscles are made up of bundles of muscle fibers, which are long and skinny. Inside these fibers are smaller units, called fibrils, which contain stringy molecules of two kinds of protein: myosin (orange) and actin (blue). When your brain tells the muscle to get shorter, or contract (when you "make a muscle"), the myosin and actin molecules slide along each other. When you stretch, they slide apart and get longer:

Now place your hand on the muscle (tricep) underneath your arm, and straighten and bend your arm again. Can you feel the tricep move? Notice that when the bicep is contracted, the tricep is stretched, and when the bicep is stretched, the tricep is contracted. Many of the muscles in your body work in opposite ways like these two. This helps to keep you balanced.

So, now do a little dance around the room, and imagine all of your muscle fibrils sliding in and out, in and out, in and out... And the next time you eat a piece of meat, look for the muscle fibers!

Talking Turkey

The centerpiece of most people's Thanksgiving dinner is the turkey. Turkey is, of course, a kind of meat, by which we usually mean the muscle tissue of an animal - beef from cows, pork from pigs, veal from calves, turkey from turkey, etc. Meat is, in general, a very nutritious food because it contains a lot of the proteins we need to stay strong and healthy (although it is possible to get those proteins without eating meat).

You've probably noticed that turkey (and chicken) meat comes in two colors, which we call white and dark. But we never see "white" beef, or "dark" fish. Why not? The color difference is due to a chemical called myoglobin which stores oxygen. Darker meats contain more myoglobin than whiter meats, and muscles that get more exercise have more myoglobin. Cows walk around a lot finding grass to eat, so they get plenty of exercise, and all of their meat is dark. Turkeys, on the other hand, stand around in pens just waiting to get fed, and they rarely, if ever, fly. Their legs and thighs work hard, but their breast muscles, which control their wings, don't do very much. So, their leg and thigh meat is dark, but the breast is white!