Amino-acid sequence, primary

Within both of the light and heavy chains are regions of amino acid sequences (primary structures) which are constant, that is, they are the same for each type of antibody molecule we will consider. There are five types of antibodies and five sets of constant amino acid sequences for the heavy chains. The light chains have a... 

Figure 25-15 Lysozyme from hen egg-white showing the amino-acid sequence (primary structure) and the four intrachain disulfide bridges. [Adapted from D. C. Phillips, Sc/. Amer. 5, 215 (1966).]...

The enormous structural diversity of proteins begins with different amino acid sequences (primary structure) of polypeptide chains that fold into complex 3D structures. The final folded arrangement of the polypeptide chain is referred to as its conformation (secondary and tertiary structures). It appears that the information for folding to the native conformation is present in the amino acid sequences (Anfinsen, 1973) however, a special class of proteins known as chaperons is required to facilitate in vivo folding of a protein to form its native conformation (Martin and Hartl, 1997). 

Proteins contain many single bonds capable of free rotation. Theoretically, therefore, proteins can assume an infinite number of possible conformations but under normal biological conditions, they assume only one or a very small number of most stable conformations. Proteins depend upon these stable conformations for their specific biological functions. A functional protein is said to be in its native form, usually the most stable one. The three-dimensional conformation of a polypeptide chain is ultimately determined by its amino acid sequence (primary structure). Changes in that sequence, as they arise from mutations in DNA, may yield conformationally altered (and often less stable, less active, or inactive) proteins. Since the biological function of a protein depends on a... 

Next, we describe the H NMR spectra of the two forms of Bomhyx mori fibroins, silk I and silk II (/3-sheet) forms, as shown in Fig. 31 (B) and (C). It should be noted that the amino-acid sequence (primary structure) of these two samples is completely identical, but their main-chain conformations are different. As expected, these two conformations are quite different to each other in terms of H CRAMPS NMR spectra. The H" signals of Bomhyx mori-I (silk-I) and Bomhyx mori-ll (silk-II) showed a singlet (h = 3.9) and doublet (S = 5.0 and 3.9), respectively. In addition, the chemical shift of the H protons... 

Figure 9.5 The amino acid sequence (primary structure) of human insulin.

If the only structural characteristics of proteins were their amino acid sequences (primary structures), all protein molecules would consist of long chains arranged in random fashion. However, protein chains fold and become aligned in such a way that certain orderly patterns result. These orderly patterns, referred to as secondary structures, result from hydrogen bonding and include the a-helix (alpha-helix) and the P-pleated (beta-pleated) sheet. 

The complete amino acid sequences (primary structure) of hemoglobins can, in principle, be determined by methods currently available. Although detailed studies of the primary structure of human and horse hemoglobins are in progress in several laboratories, the methods are so laborious that complete sequences have not yet been established. Important questions in the realm of genetics and evolution require the immediate examination of the structure, primary and other, of... 

It is important to appreciate that nmr cannot be used to determine the amino acid sequence (primary structure) of a protein. However, provided that the amino acid sequence is known, 2D nmr techniques can be used to deduce the secondary and tertiary structure of a protein (i.e. the way in which the polypeptide chain is coiled to give a-helical, -stranded or random coil regions and the way in which these re-... 

Another feature of peptide structure must be considered. The overall structure of a long polypeptide is determined by its amino acid sequence (primary structure) and whether it forms an a-helix or a P-pleated sheet (secondary structure). It is also possible to fold or coil the peptide chain into a complex, globular structure that is known as its tertiary structure. This is illustrated by the ribbon diagram for ribonuclease A, 131. The peptide chain folds and coils into a very complex structure in 131. This is the tertiary structure of the peptide. 

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