Proteins-notes

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Unformatted text preview: M. S. Shell 2010 1/38 last modified 10/19/2010 Proteins Overview Proteins are responsible for most of the chemical and physical action in cells: reactions, enzymes structure transport motoring / mechanical movement storage signaling receptor / sensing regulation of protein production Proteins are polymers of amino acids. They have many properties similar to traditional polymers, however they have two remarkable features that give them a much broader range of functionalities b we will discuss Protein composition Polymers of amino acids, made in precise sequences Each amino acid: The carbon in the center is the alpha carbon. It is a chiral center. All amino acids have L- chirality. M. S. Shell 2010 2/38 last modified 10/19/2010 The R group is called the side chain. Amino acids join together to form a peptide bond by a condensation reaction: Peptide bonds are between the carbonyl and amino groups of adjacent amino acids and are planar due to partial p character. Rotations can occur along the phi and psi angles: These rotations allow the protein polymer to assume different conformations . The backbone of the protein has amide hydrogens and carbonyl oxygens that can interact to form hydrogen bonds . N C C O H H R N C C O H H R N C C O H H R N C C O H H R amino acid residue hydrogen bond donor hydrogen bond acceptor M. S. Shell 2010 3/38 last modified 10/19/2010 Protein chains have a direction: N and C terminal parts; synthesized starting at the N terminal: Typically the termini of a protein are charged (basic/acidic) in solution. Amino acids Nature uses 20 amino acids b more are possible Often abbreviated with one-letter and three-letter codes Different chemistries so as to allow different interactions and reactions Basic kinds of amino acids hydrophobic, of varying sizes polar, uncharged polar, positively (basic) or negatively (acidic) charged Special amino acids proline rigid, cant rotate around phi angle, used to make rigid backbone glycine highly flexible, no side chain histidine easily protonated / deprotonated, useful in catalysis of many reactions cysteine can cross link through disulfide bonds using sulfur atoms, enables more stable protein structures Cysteine example: M. S. Shell 2010 4/38 last modified 10/19/2010 First amazing property of proteins : are synthesized with exact sequences of amino acids, up to long polymers with lengths of ~10000 amino acids. This contrasts synthetic polymers for which it is very hard to make with peaked molecular weight distributions or complex architectures. Protein sequences ultimately come from DNA sequences b transcription/translation machinery accomplishes this difficult task Protein folding Second amazing property of proteins : each protein adopts a unique, three dimensional conformation in aqueous solution The terminology folding is used to describe the process of going from a floppy, unstructured...
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This note was uploaded on 12/29/2011 for the course CHE 170 taught by Professor Ceweb during the Fall '10 term at UCSB.

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Proteins-notes - M. S. Shell 2010 1/38 last modified...

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