Biochemistry, 4th Edition P104. Continuing Garrett and Grisham's innovative conceptual and organizing framework, "Essential Questions," BIOCHEMISTRY guides students through course concepts in a way that reveals the beauty and usefulness of biochemistry in the everyday world. Streamlined for increased clarity and readability, this edition also includes new photos and illustrations that show the subject matter consistently throughout the text. New end-of-chapter problems, MCAT practice questions, and the unparalleled text/media integration with the power of CengageNOW round out this exceptional package, giving you the tools you need to both master course concepts and develop critical problem-solving skills you can draw upon. | How Are Proteins Processed Following Translation 993 sine kinases and steroid hormone receptors are some of the signal transduction molecules see Chapter 32 that must associate with Hsp90 in order to become fully competent proteins fitting this description are called Hsp90 client proteins. The maturation of Hsp70 client proteins requires other proteins as well and together with Hsp90 these proteins come together to form an assembly that has been called a foldosome. CFTR cystic fibrosis transmembrane regulator telomerase and nitric oxide synthase are also Hsp90-dependent. Association of nascent polypeptide chains with proteins of the various chaperone systems commits them to a folding pathway redirecting them away from degradation pathways that would otherwise eliminate them from the cell. However if these protein chains fail to fold they are recognized as non-native and targeted for destruction. How Are Proteins Processed Following Translation Aside from these folding events release of the completed polypeptide from the ribosome is not necessarily the final step in the covalent construction of a protein. Many proteins must undergo covalent alterations before they become functional. In the course of these post-translational modifications the primary structure of a protein may be altered and or novel derivations may be introduced into its amino acid side chains. Hundreds of different amino acid variations have been described in proteins virtually all arising post-translationally. The list of such modifications is very large some are rather commonplace whereas others are peculiar to a single protein. The diphthamide moiety in elongation factor eEF-2 is one example of an amino acid modification see the Human Biochemistry box on page 980 in Chapter 30 the fluorescent group of green fluorescent protein GFP see Chapter 4 is another. In addition common chemical groups such as carbohydrates and lipids may be covalently attached to a protein during its maturation.
