BiologicalMolecules160-page19

BiologicalMolecules160-page19 - and a second domain may...

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Biological Molecules - 19 Domain and Tertiary Structure Following the secondary shape, openings for bonding along the side chains (the R groups) of amino acids may fold independently into a functional unit called the domain. Domains are connected by the rest of the polypeptide. The folding of a protein into its domains is related to the hydrophilic or hydrophobic properties of its amino acids. Domain formation is part of the tertiary structure or proteins. Disulfide bonds (which are strong covalent bonds) between nearby cysteine molecules are important to the tertiary structure as well, as are hydrogen bonds, some ionic bonds between charged R-groups and van der Waals interactions. The final shape for most proteins is a globular shape. Tertiary Protein Structures Functionally, domains may perform different functions for a given protein. For example, one domain of an enzyme might be the attachment site for a co-factor
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Unformatted text preview: and a second domain may function as the active sire of the enzyme. Quaternary Protein Structure If two or more polypeptide chains join in aggregates, they form a quaternary structure, such as in the protein molecule, hemoglobin. Often quaternary proteins are complexed with a different molecule, often a mineral. Hemoglobin contains iron, for example. If two or more polypeptide chains join in aggregates, they form a quaternary structure, such as in the protein molecule, hemoglobin. Often quaternary proteins are complexed with a different molecule, often a mineral. Hemoglobin contains iron, for example. Other quaternary proteins function in cell defense, with one section anchored in the plasma membrane and a second shaped to catch invaders. H e m o g l o b i n...
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