beng100chapter4 - BENG 100 Frontiers of Biomedical...

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1 BENG 100 Frontiers of Biomedical Engineering Professor Mark Saltzman Chapter 4 SUMMARY • Linear polymers of amino acids are polypeptide chains. A protein can be composed of one or more polypeptide chains. • There are 20 different amino acids; each with its unique chemical properties conferred by the side chain. The amino acids can be placed into broad categories: polar, nonpolar, acidic, and basic. • There are four levels of structure for proteins. The amino acid sequence is the primary structure, the local domains are the secondary structure, the overall three-dimensional shape is the tertiary structure, and the formation of a complex with other polypeptide chains is the quaternary structure. • All the information necessary for a protein to fold properly into its tertiary structure is contained in the primary amino acid sequence. • Non-covalent interactions such as hydrogen bonding or the hydrophobic/hydrophilic forces hold a protein in its native form. Covalent disulfide bonds can be formed between two cysteine amino acids located at different regions of the polypeptide chain. • The three-dimensional protein structure can be determined experimentally using NMR spectroscopy or X-ray crystallography. • Proteins are often modified after translation by the addition of chemical groups to certain amino acids. • Proteins can also be processed via proteolytic cleavage of the polypeptide chain into smaller segments. • Proteins have diverse functions such as maintaining cell structure, transporting small molecules, facilitating cell communication, protecting against foreign invaders, and catalyzing chemical reactions. • Enzymes catalyze chemical reactions by lowering the activation energy of a reaction.
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2 KEY CONCEPTS AND DEFINITIONS alpha ( α ) helix – a common secondary structure of proteins in which the linear sequence of amino acids is folded into a right-handed spiral stabilized by hydrogen bonds between carboxyl and amide groups in the backbone; a coiled secondary structure of a polypeptide
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beng100chapter4 - BENG 100 Frontiers of Biomedical...

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