Tertiary and quaternary structure of

Schematic drawings of the tertiary and quaternary structures of Mb and Hb are shown in Figure 4.3 as reprinted from Figure 4.2 of reference 7.

PRIMARY, SECONDARY, TERTIARY AND QUATERNARY STRUCTURES OF PROTEINS... 

Primary, Secondary, Tertiary and Quaternary Structures of Proteins.47... 

Secondary structure, as well as tertiary and quaternary structure of proteins, is intimately dependent on the primary sequence of amino acids in the chain. In fact, the manner in which proteins fold into their ultimate structures in biological species is a subject of much research and continued uncertainty even... 

Mercaptoethanol is added to reduce the disulfide bond to disrupt the tertiary and quaternary structure of some proteins for analysis. It has a strong pungent smell. Handle sample containing 2-mercaptoethanol in a fume hood. 

D. Tertiary and quaternary structures of DNA allow even further condensation of nucleosome-coated DNA into the highly compacted structure of the chromosome (Figure 11-1). 

As described in the beginning of this chapter, the peptide bond is rigid, polar, and prefers a planar structure with hydrogen of the amino group and oxygen of the carbonyl almost trans. It is easily understood that this conformational preference and rigidity has profound implications to the tertiary and quaternary structure of proteins and similarly on the binding of smaller peptides to receptors. 

With the exception of a small group of catalytic RNA molecules (Chapter 26), all enzymes are proteins. Their catalytic activity depends on the integrity of their native protein conformation. If an enzyme is denatured or dissociated into its subunits, catalytic activity is usually lost. If an enzyme is broken down into its component amino acids, its catalytic activity is always destroyed. Thus the primary, secondary, tertiary, and quaternary structures of protein enzymes are essential to their catalytic activity. 

Tertiary and quaternary structure of proteins, glycoproteins, denaturation 21.9-21.11... 

Formaldehyde introduces both intramolecular and intermolecular crosslinks between proteins involving hydroxymethylene bridges, which change the three-dimensional structure of proteins. Such changes involve the tertiary and quaternary structures of proteins, whereas the primary and secondary structures are little affected. It has been shown that the secondary structure of purified protein molecules remains mostly unaltered during fixation with formaldehyde (Mason and O Leary, 1991). Even when the quaternary structure is changed by formaldehyde fixation, the secondary structure can remain intact. 

VIII. Influence of Salt Bridges on Tertiary and Quaternary Structures of Hemoglobin... 

NES represents the product of a reaction between Af-ethylmaleimide and the sulfhydryl group of (393 cysteine. Attaching NES to the sulfhydryl group of Cys((393) inhibits the formation of the salt bridge between His( 3146) and Asp(094). H NMR spectroscopy was used to investigate these modified Hbs and thus to assess the influence of the salt bridges located at the carboxy terminals of both the a and (3 chains on the tertiary and quaternary structures of Hb (for details, refer to Miura and Ho, 1984). 

Fifth, we have prepared cross-linked modified hemoglobins—[a(des-Arg)0]A[a0]cXL, [a(des-Arg-Tyr)0]A[a0]cXL, [a(des-Arg)0(NES)]A [a0]cXL, and [a(des-Arg)0]A[a0(NES)]cXL—and used them to investigate the influence of salt bridges on tertiary and quaternary structures of Hb by H NMR spectroscopy (Miura and Ho, 1984). We have found that several features of the H NMR spectra of asymmetrically modified Hbs cannot be accounted for as a spectral sum of the intact dexoy-Hb C and chemically modified Hb A. The H NMR spectra of deoxy [a(des-Arg)0(NES)]A[a0]cXL and deoxy[a(des-ARG)0]A[a0(NES)]cXL at low pH (pH —6.0) cannot be explained simply as a sum of the spectral features specific for the deoxylike and the oxylike quaternary structures. Thus, our results suggest that there exist intermediate structures in which the tertiary and quaternary structural transitions occur asymmetrically about the diad axis of the Hb molecule during the course of successive removal of the salt bridges (Miura and Ho, 1984). 

Secondary, tertiary, and quaternary structures of a protein are mainly stabilized by hydrophobic interactions, van der Waals forces, and by hydrogen bonds. 

The conformation of a protein in a particular environment affects its functional properties. Conformation is governed by the amino acid composition and their sequence as influenced by the immediate environment. The secondary, tertiary and quaternary structures of proteins are mostly due to non-covalent interactions between the side chains of contiguous amino acid residues. Covalent disulfide bonds may be important in the maintenance of tertiary and quaternary structure. The non-covalent forces are hydrogen bonding, electrostatic interactions, Van der Waals interactions and hydrophobic associations. The possible importance of these in relation to protein structure and function was discussed by Ryan (13). 

The diversity in primary, secondary, tertiary, and quaternary structures of proteins means that few generalisations can be made concerning their chemical properties. Some fulfil structural roles, such as the collagens (found in bone) and keratin (found in claws and beaks), and are insoluble in all solvents. Others, such as albumins or globulins of plasma, are very soluble in water. Still others, which form part of membranes of cells, are partly hydrophilic ( water-loving , hence water-soluble) and partly lipophilic ( lipid-loving , hence fat-soluble). 

Now that you have learned some of the chemistry of amino acids, it s time to study proteins, the large polymers of amino acids that are responsible for so much of the structure and function of all living cells. We begin with a discussion of the primary, secondary, tertiary, and quaternary structure of proteins. 

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