Residual acid

Proteins consist of large numbers of amino-acids joined by the p>eptide link —CO —NH — into chains, as shown in the diagram, where R and R" are amino-acid residues. These chains are called peptides and may be broken into smaller chains by partial hydrolysis (see peptides). Proteins may contain more than one peptide chain thus insulin consists of... 

Table 1. Effects of neutralization of some acidic residues on the pK of Serl7 residue of the substrate...

HyperChem contains a database of amino and nucleic acid residues so you can quickly build polymers con laining these subunits. You can also read in structures in files from standard databases, such as the Brookhaven Protein Data Bank (see the HyperChem Reference Manual). 

The OPLS force field is described in twtt papers, one discussing parameters for proteins W. L. Jorgensen and J. Tirado-Rives,/. Amer. (. hem. Soc., 110, 1557 (iy8K) and on e discii ssin g param eters for n iicleotide bases [J. Pranata, S. Wiersch ke, and W. L. Jorgen sen. , /.. Amer. Chem. Soc.. 117, 281(1 ( 1991)1. The force field uses the united atom concept ftir many, but not all. hydrttgens attached to carbons to allow faster calculation s on macromolecular systems. The amino and nucleic acid residue templates in HyperChein automatically switch to a united atom representation where appropriate when th e OPLS option is selected. 

The role of the base is apparently primarily that of a proton remover from the reactive methylene group thus if B represents the base, reaction (i) gives the carbanion, which then combines with the positive carbon of the carbonyl group (reaction ii) the product regains a proton from the piperidinium ion, and then by loss of water followed by mono-decarboxylation of the malonic acid residue gives the final acid. 

The Stobbe condensation thus provides a method for introducing a propionic acid residue at the site of a carbonyl group. 

Sanger also determined the sequence of the A chain and identified the cysteine residues involved m disulfide bonds befween fhe A and B chains as well as m fhe disulfide linkage wifhin fhe A chain The complefe insulin sfruefure is shown m Figure 27 11 The sfruefure shown is fhaf of bovine insulin (from cattle) The A chains of human insulin and bovine insulin differ m only fwo ammo acid residues fheir B chains are identical except for the ammo acid at the C terminus... 

By successively adding ammo acid residues to the C terminal ammo acid it took Memfield only eight days to synthesize bradykmm m 68% yield The biological activ ity of synthetic bradykmm was identical with that of natural material... 

Step 4 The Boc protecting group is removed as m step 2 If desired steps 3 and 4 may be repeated to introduce as many ammo acid residues as desired... 

FIGURE 27 15 Peptide synthesis by the solid phase method Ammo acid residues are attached sequentially beginning at the C terminus... 

Section 27 18 In the Memfield method the carboxyl group of an ammo acid is anchored to a solid support and the chain extended one ammo acid at a time When all the ammo acid residues have been added the polypeptide is removed from the solid support... 

What are the products of each of the following reactions Your answer should account for all the ammo acid residues m the starting peptides... 

This reaction forms the basis of one method of terminal residue analysis A peptide is treated with excess hydrazine in order to cleave all the peptide linkages One of the terminal amino acids is cleaved as the free amino acid and identified all the other ammo acid residues are converted to acyl hydrazides Which amino acid is identified by hydrazmolysis the N terminus or the C terminus ... 

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

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