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Proteins

Properties Of Amino Acids, Primary Structure, Secondary Structure And Motifs, Tertiary Structure And Protein DomainsMolecular Chaperones, Proteomics

Proteins are polymers of amino acids that provide structure and control reactions in all cells. When humans think of expressing the meaning of life, they often resort to words. From poems to sonnets to short stories to novels, words tell the stories of life. But in biological terms, the words of life are proteins. While DNA holds the code of life, proteins are the language in which that code is expressed.

Computer generated representation of the enzyme neuraminidase (ribbons and strings) with an inhibitor (ball and stick) in the active site, a cleft on the enzyme's surface. This tertiary structure is built up from the primary structure (amino acid structure) and secondary structure. The arrows represent the beta-pleated sheet, a type of secondary structure.

To observe the mosaic of proteins in life is to observe nature in its finest array. The feathers of a bird and the silk of a spider's web are both almost pure protein. The most numerous proteins in an animal are the collagen proteins joining animal body parts. Other proteins include the positively charged histone proteins that condense the cell's negatively charged DNA and the transcription factor proteins that control which genes are expressed (made into proteins) and which remain silent. A plant traps CO2 to make sugar with Earth's most abundant protein, the enzyme ribulose 1,5-biphosphate carboxylase. The protein hemoglobin transports gases through the bloodstream necessary for the metabolism of life. Other proteins store minerals (ferritin) or fats (ovalbumin), contract muscles (myosin), protect against infection (anti-bodies), or act as toxins (botulinum) or hormones (insulin).

Although the folding of the protein into its tertiary structure is determined by the primary order of amino acids, the process of folding occurs with the assistance of molecular chaperone proteins. These molecular chaperones often have pockets or tunnels that envelop the nascent polypeptide. This enveloping allows the folding of the protein to occur unhindered by unwanted interaction with other cellular components.

Proteomics is a new field of study that seeks to describe which proteins are expressed in a cell, when they are expressed, what consequences result from their expression, and how they fit into biochemical pathways. The first step in the study of proteomics is to define the language of protein structure. The field of proteomics promises to bring a complex understanding to the role of proteins in living cells.

Paul K. Small

Bibliography

Fairbanks, Daniel, J., and W. Ralph Anderson. Genetics: The Continuity of Life. PacificGrove, CA: Brooks/Cole, 1999.

Lodish, Harvey, et al. Molecular Cell Biology, 4th ed. New York: W. H. Freeman, 2000.

Sadava, David E. Cell Biology: Organelle Structure and Function. Boston: Jones and Bartlett, 1993.

Stryer, Lubert. Biochemistry, 3rd ed. New York: W. H. Freeman, 1988.

Additional topics

Medicine EncyclopediaGenetics in Medicine - Part 3