Biochemistry, 4th Edition P12. 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. | What Are the Structures and Properties of Amino Acids 73 d Basic FIGURE continued 74 Chapter 4 Amino Acids CENGAGENOW Go to CengageNOW at www . login and click BiochemistryInteractive to find out how many amino acids you can recognize and name. Nonpolar Amino Acids The nonpolar amino acids Figure are critically important for the processes that drive protein chains to fold that is to form their natural and functional structures as shown in Chapter 6. Amino acids termed nonpolar include all those with alkyl chain R groups alanine valine leucine and isoleucine as well as proline with its unusual cyclic structure methionine one of the two sulfur-containing amino acids and two aromatic amino acids phenylalanine and tryptophan. Tryptophan is sometimes considered a borderline member of this group because it can interact favorably with water via the N H moiety of the indole ring. Proline strictly speaking is not an amino acid but rather an a-imino acid. Polar Uncharged Amino Acids The polar uncharged amino acids Figure except for glycine contain R groups that can 1 form hydrogen bonds with water and 2 play a variety of nucleophilic roles in enzyme reactions. These amino acids are usually more soluble in water than the nonpolar amino acids. The amide groups of asparagine and glutamine the hydroxyl groups of tyrosine threonine and serine and the sulfhydryl group of cysteine are all good hydrogen bond-forming moieties. Glycine the simplest amino acid has only a single hydrogen for an R group and this hydrogen is not a good hydrogen bond former. Glycine s solubility properties are mainly influenced by its polar amino and carboxyl groups and thus glycine is best considered a member of the polar uncharged group. It should be noted that tyrosine has significant nonpolar characteristics due to its aromatic ring and could arguably be placed in the nonpolar group. However with a pKa of tyrosine s phenolic hydroxyl is a charged polar entity at high .
