Figure 218

Hydrogen bonds between regularly spaced peptide bonds can produce a helical conformation in a polypeptide chain.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART ONE Basic Cell Functions

TABLE 2-6 Bonding Forces Between Atoms and Molecules

Bond

Strength

Characteristics

Examples

Hydrogen

Weak

Electrical attraction between polarized bonds, usually hydrogen and oxygen

Attractions between peptide bonds forming the alpha helix structure of proteins and between polar amino acid side chains contributing to protein conformation; attractions between water molecules

Ionic

Strong

Electrical attraction between oppositely charged ionized groups

Attractions between ionized groups in amino acid side chains contributing to protein conformation; attractions between ions in a salt

van der Waals

Very weak

Attraction between nonpolar molecules and groups when very close to each other

Attractions between nonpolar amino acids in proteins contributing to protein conformation; attractions between lipid molecules

Covalent

Very strong

Shared electrons between atoms

Nonpolar covalent bonds share electrons equally while in polar bonds the electrons reside closer to one atom in the pair

Most bonds linking atoms together to form molecules

Beta Sheet

FIGURE 2-19

A ribbon diagram illustrating the pathway followed by the backbone of a single polypeptide chain. Helical regions (blue) are coiled, beta sheets (red) of parallel chains are shown as relatively straight arrows, and loop conformations (yellow) connect the various helical and beta sheet regions. Beginning at the end of the chain labeled "Beta sheet," there is a continuous chain of amino acids that passes through various conformations.

FIGURE 2-19

A ribbon diagram illustrating the pathway followed by the backbone of a single polypeptide chain. Helical regions (blue) are coiled, beta sheets (red) of parallel chains are shown as relatively straight arrows, and loop conformations (yellow) connect the various helical and beta sheet regions. Beginning at the end of the chain labeled "Beta sheet," there is a continuous chain of amino acids that passes through various conformations.

three-dimensional conformations have been determined for only a few. Because of the multiple factors that can influence the folding of a polypeptide chain, it is not yet possible to predict accurately the conformation of a protein from its primary amino acid sequence.

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