Prosthetic groups tertiary structure

Describe, using a suitable example, each of the following (a) a prosthetic group, (b) a peptide link, (c) a S-S bridge and (d) the tertiary structure of a protein. 

Circular dichroism (CD) spectroscopy is a sensitive analytical tool for assessing protein structure. It can detect changes in both the secondary and tertiary structure of proteins, as well as provide information regarding prosthetic groups, bound ligands and co-factors. The origin of circular dichroism in proteins is described and various applications of CD spectroscopy to the study of protein structure, function, and folding is discussed. 

The apparent absence in the transferrins of any prosthetic group or chemical structure uncommon to proteins might suggest that the transferrins contain some unusual sequences of amino acids or some unusual juxtaposition of residues in the tertiary structure. Unfortunately, there is no sequence data available and very little is known about tertiary structure so the information presently available is essentially nothing more than sterile listings of amino acid compositions. 

Metalloproteins constitute a distinct subclass of proteins that are characterized by the presence of single or multiple metal ions bound to the protein by interactions with nitrogen, sulfur, or oxygen atoms of available amino acid residues or are complexed by prosthetic groups, such as heme, that are covalently linked to the protein. These metals function either as catalysts for chemical reactions or as stabilizers of the protein tertiary structure. Protein-bound metals may also be labile and, as such, be subject to transport, transient storage, and donation to other molecular sites of requirement within tissues and cells. 

Tertiary structure includes the three-dimensional arrangement of all the atoms in the protein, including those in the side chains and in any prosthetic groups (groups of atoms other than amino acids). 

The tertiary structure of a protein is the three-dimensional arrangement of all the atoms in the molecule. The conformations of the side chains and the positions of any prosthetic groups are parts of the tertiary structure, as is the arrangement of helical and pleated-sheet sections with respect to one another. In a hbrous protein, the overall shape of which is a long rod, the secondary structure also provides much of the information about the tertiary structure. The helical backbone of the protein does not fold back on itself, and the only... 

For a globular protein, considerably more information is needed. It is necessary to determine the way in which the helical and pleated-sheet sections fold back on each other, in addition to the positions of the side-chain atoms and any prosthetic groups. The interactions between the side chains play an important role in the folding of proteins. The folding pattern frequently brings residues that are separated in the amino acid sequence into proximity in the tertiary structure of the native protein. 

Almost nothing is known about the tertiary structure of most proteins, because crystal-structure analyses are unusually laborious. Hemoglobin and myoglobin are the only proteins whose arrangement of peptide chains in space is known (Perutz Kendrew). Fundamentally, the structure consists of a-helix portions that are draped in an irregular double loop around the prosthetic group. Myoglobin is... 

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