TAILIEUCHUNG - Biochemistry, 4th Edition P23

Biochemistry, 4th Edition P23. 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 Is the Structure and Chemistry of Monosaccharides 183 Carbon number 1 CH2OH I 2 C O I 3 CH2OH KETOTRIOSE Dihydroxyacetone 1 CH2OH I 2 C O Carbon number 3 hCoH I 4 CH2OH KETOTETROSE Carbon number D-Erythrulose CH2OH I CO I HOCH I HCOH I CH2OH D-Xylulose KETOPENTOSES Carbon number 1 CH2OH I 2 C O I 3 HCOH I 4 HCOH I 5 HCOH I 6 CH2OH CH2OH I CO HOCH HCOH I HCOH I CH2OH CH2OH I CO I HCOH I HOCH I HCOH I CH2OH CH2OH I CO I HOCH I KETOHEXOSES HOCH I HCOH I CH2OH D-Psicose D-Fructose D-Sorbose D-Tagatose FIGURE The structure and stereochemical relationships of D-ketoses with three to six configuration in each case is determined by the highest numbered asymmetric carbon shown in pink . In each row the new asymmetric carbon is shown in yellow. Blue highlights indicate the most common ketoses. Monosaccharides either aldoses or ketoses are often given more detailed generic names to describe both the important functional groups and the total number of carbon atoms. Thus one can refer to aldotetroses and ketotetroses aldopentoses and ketopentoses aldohexoses and ketohexoses and so on. Sometimes the ketone-containing monosaccharides are named simply by inserting the letters -ul-into the simple generic terms such as tetruloses pentuloses hexuloses heptuloses and so on. The simplest monosaccharides are water soluble and most taste sweet. Stereochemistry Is a Prominent Feature of Monosaccharides Aldoses with at least three carbons and ketoses with at least four carbons contain chiral centers see Chapter 4 . The nomenclature for such molecules must specify the configuration about each asymmetric center and drawings of these molecules must be based on a system that clearly specifies these configurations. As noted in Chapter 4 the Fischer projection system is used almost universally for this purpose today. The structures shown in Figures and are Fischer projections. For monosaccharides with two or more asymmetric carbons the prefix D or L refers to the

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