Globular proteins, structure-forming

The Structure of the a-Keratins Was Determined with the Help of Molecular Models The fi-Keratins Form Sheetlike Structures with Extended Polypeptide Chains Collagen Forms a Unique Triple-Stranded Structure Globular Protein Structures Are Extremely Varied and Require a More Sophisticated Form of Analysis Folding of Globular Proteins Reveals a Hierarchy of Structural Organization... 

Globular Protein Structures Are Extremely Varied and Require a More Sophisticated Form of Analysis... 

We have seen that the forces that maintain the secondary structure of a protein are hydrogen bonds between the amide hydrogen and the carbonyl oxygen of the peptide bond. What are the forces that maintain the tertiary structure of a protein The globular tertiary structure forms spontaneously and is maintained as a result of interactions among the side chains, the R groups, of the amino acids. The structure is maintained by the following molecular interactions ... 

FIGURE 4-15 Globular protein structures are compact and varied. Human serum albumin (M, 64,500) has 585 residues in a single chain. Given here are the approximate dimensions its single polypeptide chain would have if it occurred entirely in extended fi conformation or as an a helix. Also shown is the size of the protein in its native globular form, as determined by X-ray crystallography the polypeptide chain must be very compactly folded to fit into these dimensions. 

Globular protein (Section 27 20) An approximately spheri cally shaped protein that forms a colloidal dispersion in water Most enzymes are globular proteins Glycogen (Section 25 15) A polysaccharide present in animals that IS denved from glucose Similar in structure to amy lopectin... 

Hydrogen bonding stabilizes some protein molecules in helical forms, and disulfide cross-links stabilize some protein molecules in globular forms. We shall consider helical structures in Sec. 1.11 and shall learn more about ellipsoidal globular proteins in the chapters concerned with the solution properties of polymers, especially Chap. 9. Both secondary and tertiary levels of structure are also influenced by the distribution of polar and nonpolar amino acid molecules relative to the aqueous environment of the protein molecules. Nonpolar amino acids are designated in Table 1.3. 

X-ray diffraction analysis reveals the three-dimensional structure of both IL-l molecules to be quite similar. Both are globular proteins, composed of six strands of antiparallel P pleated sheet forming a barrel that is closed at one end by a further series of P sheets. 

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