Molecular fingerprints  pg. 3

  1. John Roberts, M.D., left, chief of general thoracic surgery, removes a lung tumor with the help of surgery resident John Stewart, M.D.
  2. The tumor, removed from the left lung, is about an inch long.
  3. Adriana Gonzalez, M.D., examines a lung tumor in the surgical pathology lab.
  4. Slices of a tumor are prepared for a mass spectrometry study.
  5. Kiyoshi Yanagisawa, M.D., Ph.D., reads the mass spectrum of proteins in a tumor.
Photos by 1 & 2:  Dana Johnson, 3, 4 & 5: Anne Rayner
While humans apparently have fewer genes than it takes to make a rice plant, there are hundreds of thousands of different human proteins, perhaps more than a million.

The diversity and complexity of proteins is absolutely mind-boggling.

Insulin, which carries sugar into the cells for fuel, is made up of two polypeptide chains, one with 30 amino acids and the other with 21. Hemoglobin, the oxygen-carrying protein in red blood cells, is a complex three-dimensional molecule with four chains, each more than 140 amino acids long. The epidermal growth factor receptor, a target for some of the new cancer drugs, is a single-chain protein with nearly 1,200 amino acids (see “One Protein’s Story”).

Proteins also have many different jobs. They form the elastic and resilient framework of muscles, nerves and other body tissues. They carry signals within and between cells, and -- in the case of antibodies -- sound the alarm when a germ invades. Many of them are enzymes, catalyzing chemical reactions. Still others help “read” the genetic code so it can be “translated” into more proteins.

Scientists used to think that for every gene there was only one protein. They now know that while genes determine the sequence of amino acids that make up the protein backbone, the genetic instructions can be translated and implemented in more than one way.

Once produced, proteins can be modified—by the addition of a phosphate or sugar molecule, for example—in ways that change their shape and function. And while our double-helical string of genes is relatively static and unchanging, proteins are constantly in motion. Some proteins come on the scene just long enough to do their jobs, and then -- in a blink of an eye -- they’re gone.

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