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Proteins

 

Overview

Proteins run our show. Muscles, organs, hair, bone, and skin either contain or are made of proteins. They are a major component in all of our cells. Enzymes that run the chemical reactions in our bodies are proteins. Proteins help us move, send messages (hormones and nerve receptors), fight off disease (antibodies), and transport other molecules and atoms around our bodies. A protein is a molecule that consists of a chain of amino acids. There are 20 different amino acids to choose from, and the genetic information in our DNA determines how they're put together. A single protein consists of hundreds of amino acids, all folding into a structure with a specific shape. What job a protein does in the body is determined by its structure (its conformation) and the way it moves (its dynamics). Hemoglobin, for example, is an important red blood cell protein that delivers oxygen to tissues and hauls carbon dioxide to the lungs for removal. In the lungs, oxygen binds to the iron atoms inside a hemoglobin molecule and any attached carbon dioxide is released. In the tissues, the molecules of oxygen are released and more carbon dioxide is picked up. As illustrated in the video segment, it is the motions of parts of the hemoglobin molecule that makes this binding and release action work. Scientists can investigate these motions or dynamics as well as the protein's structure using a technique called NMR (nuclear magnetic resonance) spectroscopy. The nuclei of some atoms are like little magnets; they align within a magnetic field. If disturbed by a very quick blast of radio waves, this alignment is disrupted and these little magnets gradually relax back into alignment with the field. Researchers can interpret this NMR relaxation to get very detailed information about molecular motion and how proteins do their many different tasks in the body.

Activity

Scientists describe the structure of proteins several different ways, from the sequence of amino acids ­the basic building blocks of protein­ to how proteins interact. Some of the basic structures of proteins are recognizable; one is the alpha­helix, which looks like an open spiral staircase. Another is the beta­sheet, which resembles a picket fence. In this activity, you'll build a model of a protein with four helix units. Materials (per group of four)
  • four 10" ­ 12" cardboard tubes (from plastic wrap or aluminum foil)
  • four 30" ­ long pieces of Velcro (with peel-off sticky back)
  • cotton balls
  • Ping-Pong or golf ball 1. Each member of the group will make one helix: Hold one of the tubes vertically and wrap the Velcro strip around the tube in a spiral pattern. Attach the cotton balls to the Velcro an inch apart from each other. Can you see how this resembles a helix structure of a protein? What do the cotton balls represent? 2. Position four tubes together so that the cotton balls of one tube touch the Velcro strip of another. They should be able to hold together this way. What happens if you combine yours with another group's? 3. Now take the Ping­Pong or golf ball and try to get it into the middle of your four helices. What do you have to do to get it to fit inside? How is this similar to what a protein does to accommodate a smaller molecule? What kinds of molecules change their conformation like this to do their job? Questions Why is it important for researchers to know the shapes of different proteins? How do you think they are able to alter a protein's shape?
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