Identifying Unknown Proteins. Since several different proteins may have the same mass, simply obtaining the mass of the whole protein is not enough to identify it. However, if it is broken into a characteristic set of fragments peptides amino acid (called peptides), and the mass of each of these is determined, it is usually chains possible to identify the protein based on its "peptide fingerprint."

Sequencing Peptides. Peptides can be sequenced by generating multiple sets of fragments and analyzing the differences in masses among them. Removing a single amino acid from a peptide, for instance, will decrease its mass by a specific amount and at the same time create a new, detectable particle with the same mass. Individual amino acids can be identified by their characteristic molecular masses. Mass spectrometry has made protein sequencing much easier than it had been. The traditional method required about twelve hours to sequence a ten-amino acid peptide. Mass spectrometry can do the same job in about one second. The entire protein need not be sequenced to be identified. Often four to five amino acids are enough.

Identifying Chemical Modifications. Chemical modifications to proteins after they are synthesized (called post-translational modifications) are important for regulation. For instance, the addition of a phosphate group (PO4) is used to turn on or turn off many enzymes. The presence of such groups can be detected by the additional weight they bring. Sugar groups can be detected in the same fashion. see also Bioinformatics; HPLC: HighPerformance Liquid Chromatography; Internet; Post-Translational Control; Proteins; Proteomics.

Richard Robinson


Perkel, Jeffrey M. "Mass Spectrometry Applications for Proteomics." The Scientist 15, no. 16 (2001): 31-32.

Internet Resource

Mass Spectrometry. Richard Caprioli and Marc Sutter, eds. Vanderbilt University Mass Spectrometry Research Center. <>.

McClintock, Barbara

Geneticist 1902-1992

Barbara McClintock was one of the most important geneticists of the twentieth century and among the most controversial women in the history of science. She made several fundamental contributions to our understanding of chromosome structure, put forward a bold and incorrect theory of gene regulation, and, late in her career, developed a profound understanding of the interactions among genes, organisms, and environments. She was born on June 16, 1902, in Hartford, Connecticut, the third of four children and the youngest daughter. She grew up in Brooklyn, New York, and in 1919 she enrolled in the agricultural college of Cornell University, where she received all her post-secondary education. She took a bachelor's degree in 1923, a master's in 1925, and a Ph.D., under the direction of the cytologist Lester Sharp, in 1927.

McClintock gravitated toward the cytology and genetics of maize, or Indian corn, and by 1929 she was a rising star in her field. Not quite single-handedly, she made possible the "golden age of maize genetics," from 1929 to 1935. During those years, McClintock published a string of superb papers identifying novel cytological phenomena and linking them to genetic events. Working with Harriet Creighton, she confirmed that chromosomes physically exchange pieces during the genetic phenomenon known as "crossing over." She was supported by a series of prestigious fellowships, from the National Research Council, the Guggenheim Foundation, and others, that took her from Cornell to the California Institute of Technology, and to Berlin and back. In 1935 she took a faculty position at the University of Missouri in Columbia. She was not happy there, however, and resigned in 1939, despite the apparent imminence of a promotion with tenure.

In 1941 she took a summer position at Cold Spring Harbor on New York's Long Island, at the Carnegie Institution of Washington's Department of Genetics. It was an ideal position for her, with no teaching or administrative duties. Within a year the post became permanent, and she remained there until her death. On arrival, she continued work that she had begun while at Missouri, investigating a phenomenon called the breakage-fusion-bridge (BFB) cycle. This is a repeating pattern of chromosome breakage she had discovered among strains of maize plants grown from X-rayed pollen. In 1944, during an experiment designed to use the BFB cycle to create new mutations, she discovered numerous "mutable" genes: genes that turned on and off spontaneously during development. In the cells of some of these new mutants lay her most important discovery, chromosome segments that move from place to place on the chromosome. That same year, the National Academy of Sciences honored a woman for only the third time in its eighty-year history when it elected McClintock a member.

During the rest of the 1940s McClintock developed a novel theory of how genes could control the development and differentiation of organisms.

Barbara McClintock, having just received the prestigious $15,000 Lasker Award in 1981 for her many contributions to the field of genetics.

cytologist a scientist who studies cells

0 0

Post a comment