Primary, Secondary, Tertiary, and Quaternary Structure of Proteins

PRIMARY, SECONDARY, TERTIARY, AND QUATERNARY STRUCTURE OF PROTEINS 

Primary struclure (amino acid sequence in a polypeptide chain) 

Quaternary structure the four separate chains of hemoglobin assembled into an oligomeric protein 

FIGURE 3.6 Structural organisation of proteins. (From Voet Voet, 2004. Reproduced with permission from John Wiley Sons, Inc.) 

We know, from the classic experiments of Christian B. Anfinsen (Anfinsen, 1973), that the amino acid sequence inherently contains all the information required for the overall three-dimensional structure of the protein (but, we still do not yet know how to predict the latter accurately from the former). The secondary 

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

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. 

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. 

Figure 28.15 The primary, secondary, tertiary, and quaternary structure of proteins...

Primary, Secondary, Tertiary, and Quaternary Structure of Proteins Secondary and Tertiary Structures of Nucleic Acids... 

Recognize the amino adds and understand how they form peptides and proteins via amide bond formation. (Section 24.7) Understand the differences among the primary, secondary, tertiary, and quaternary structures of proteins. (Section 24.7)... 

Fig. 20. Primary, secondary, tertiary, and quaternary structure of proteins. In the secondary structure, the small unlettered circles represent hydrogen atoms, R = sidechains of the amino acids. In the tertiary structure the black disc represents the hemin group. In the quaternary structure the two a-chains of hemoglobin are white, the two /3-chains black. One of them is easy to distinguish from the white background of the a-chains (modified from Sund as presented in Wieland and Pfieiderer 1969).

Armed with these new insights into primary, secondary, tertiary, and quaternary structure of proteins, let us now return to the question of the relation one gene-one polypetide. In doing so we will not concern ourselves with the enumeration of instances of one gene-one enzyme relationships. (There is a variety of obvious examples in higher plants.) Instead we want to verify whether in fact one gene does induce one polypeptide, which can then, possibly, combine with other polypeptides of the same or a slightly different kind to form a quaternary structure. To do this we must study isoenzymes. 

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