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Physiologically important ketoses and their common names. Systematic names are shown in parentheses. neuraminic acid, a nine-carbon acidic ketose, is an important signaling epitope in glycoproteins. The abbreviations or symbols for the sugars usually consist of the first three letters of their names (Table 1-1). Glucose (Glc) and some ketoses are exceptions to this rule.

Classification

Carbohydrates are defined as polyhydroxy aldehydes (the aldoses) and ketones (the keto-ses) or derivatives of these sugars. This definition emphasizes the hydrophilic nature of most carbohydrates and allows inclusion of sugar alcohols (alditols), sugar acids (uronic, aldonic, and aldaric acids), glycosides, and polymerized products (oligosaccharides and polysaccharides) among the classes of carbohydrates. The hydroxyl groups of carbohydrates may be modified by substitution with other groups to...

Alditols

The alditols polyois Fig. 1-8 , which occur naturally in plants and other organisms, are reduction products of aldoses and ketoses in which the carbonyl has been reduced to an alcohol. Reduction of ketoses, however, gives an epimeric pair of alditols unless the reaction is enzyme catalyzed and therefore stereospe-cific. The alditols, like the sugars, are soluble in water and vary in degree of sweetness. Xylitol, the sweetest, approaches the sweet- Figure 1-8. Structures of the common sugar...

Digestible Polysaccharides

Structure Cellulose

Starch and glycogen are digestible polysaccharides of glucose. Starch is found in plant cells, in both linear and branched forms. Glycogen has a highly branched structure and is found in animal tissues, particularly muscle and liver. Starch. Starch is one of the most abundant polysaccharides in plants, where it is stored in the seeds, tubers, roots, and some fruits. It is composed of two families of polymers, a mostly linear amylose 1 4 -oH gt glucan and the branched amylopectin l- gt 4...

Amino Acids

An understanding of the chemical and structural features of amino acids, peptides, and proteins is essential from a number of perspectives. For nutritionists, there is the need to appreciate the essential nature of amino acids and the dietary aspects of peptides and proteins as nutrients. There is also the obvious importance of amino acids, peptides, and proteins as informational and regulatory molecules. This chapter focuses on the chemical characteristics of amino acids and their role in...

Sugar Protein Reactions in Diabetes and Aging

The Maillard Amadori reactions of sugars with amino acids and proteins lead to a cascade of reactions. Products of these reactions are referred to as advanced glycation end products. These reaction end products have been observed in collagen-rich tissues in vivo and in vitro, and they are associated with stiffening of artery walls, lung tissue, and joints and with other aging symptoms. Considerable evidence links hyperglycemia with increased formation of these end products these products...

Glycolipids

Glycolipids are widespread in nature but only as minor components of the lipid fraction and usually associated with proteins. The common glycolipids of mammalian systems include cerebrosides and gangliosides, which are gly-cosyl glucosyl or galactosyl derivatives of sphingolipids Table 1-5 . These glycosphin-golipids contain a base such as sphingosine, which has an 18-carbon monounsaturated chain substituted with two hydroxyl groups and an amine group. The amine nitrogen of the sphingosine unit...

Polysaccharides Of Nutritional Importance

Polysaccharides are polymers composed of sugars linked by glycosidic bonds and varying in size from about 20 to over 107 sugar units degree of polymerization . Because of the multiple hydroxyl groups in monosaccharides, which serve as linkage sites for glycosidic bonds, there is opportunity for great structural diversity in polysaccharides. The structural diversity includes molecular size, kinds and proportions of sugars, ring size furanose or py-ranose , anomeric configuration a or , and...

Structure and Properties of the Macronutrients

Water H20 Plants

Nutrition may be defined simply as the utilization of foods by living organisms for normal growth, reproduction, and maintenance of health. The compounds that are classed as nutrients include water, carbohydrates, proteins or amino acids, lipids, vitamins, and minerals. These nutrients make up living tissues whether they be plant, animal, or microbial tissues. Thus, these nutrients are obtained by intake of food and are then used by the human body to build and maintain its own tissues. The...

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Titration Curve Alanin

Examples of posttranslationally modified and less conventional amino acids. A , Some of the modifications are the result of specific enzymatic reactions wherein the amino acid to be modified is first incorporated into a given peptide or protein and then altered by an enzyme-catalyzed reaction. Examples of the products of a methylation t-n-trimethyllysine residue formation , sulfation tyrosine sulfate residue formation , hydroxylation 5-hydroxylysine residue formation , and a...

Digestion and Absorption of the Macronutrients

Macronutrient Digestion And Absorption

Some of the earliest investigations of biochemical and physiological events involved the study of the digestive fluids and processes. In 1822, William Beaumont, an American physician, studied gastric juice obtained from a gastric fistula that remained in a patient who had recovered from a gunshot wound. This led to the discovery that hydrochloric acid was secreted into the stomach. In 1836, the German anatomist and physiologist Theodor Schwann described the ability of gastric juice to break...

Deoxy and Amino Sugars

Several common sugars lack the complete complement of hydroxyl groups examples of these are shown in Figure 1-10. Deoxy sugars, in which a hydroxyl group is replaced by a hydrogen, include 2-deoxy-D-ribose, L-fucose 6-deoxy-L-galactose , and L-rhamnose 6-deoxy-L-mannose . L-Fucose is a constituent of many glycoproteins and serves as a signaling epitope for physiological events for example, in the inflammatory response. The presence of fucose in crucial oligosaccharides of cell surface...

Glycuronic Glyconic and Glycaric Acids

The uronic acids are weak sugar acids that have a carboxyl group COOH instead of the terminal CH2OH Fig. 1-9 . d-G1ucu-ronic acid is an important constituent of gly-cosaminoglycans in mammalian systems, and its C-5 epimer, l-iduronic acid, is present to a lesser extent. Glucuronic acid and its 4-0-methyl ether , d-galacturonic acid, d-mannu-ronic acid, and the less common l-guluronic Figure 1-9. Carboxylic acid derivatives of d-giucose and l-idose. d-Gluconic acid is shown along with its...

Structural Repeating Units of the Glycosaminoglycans Showing Sulfation Patterns and Structural Varia

-GalNAc p l-4 GlcA pi-3 gt 4 or 6 -GalNAc pi-4 L-IdoA otl-3 - 4 2 -GalNAc pi-4 GlcA pi-3 - 4 or 6 -Gal P1-4 GlcNAc 31-3 - 6 6 -GlcNR al-4 GlcA il-4 - 6 R Ac or SO With the exception of hyaluronan and keratan sulfate, the glycosaminoglycans are glycosidically linked to a protein chain by the sequence Keratan sulfate is glycosidically linked to the N- or O-linked oligosaccharides of some glycoproteins. Sugars are d unless noted as l. Hyaluronan is not covalently linked to proteins. fR in the...

The Acid and Base Characteristics of Amino Acids

When an amino acid is titrated i.e., exposed to an acid or base , the resulting reactions can be described by a titration curve. The shape of this curve is influenced by the types and number of the functional groups capable of reacting with or exchanging a hydrogen ion. In an amino acid such as alanine, there are two titratable groups Fig. 2-4 . At a low pH i.e., a high hydrogen ion concentration , both the amino group and the carboxylic acid group of alanine are protonated. As a result,...

Structures of the Aldoses and Ketoses

D-Aldoses are related to d-glyceraldehyde as can be illustrated by their chemical synthesis from d-glyceraldehyde Fig. 1-1 . l-Aldoses are similarly related to l-glyceraldehyde. In this synthetic scheme, a nucleophilic cyanide ion CN adds to the carbonyl double bond C-1 of glyceraldehyde, giving two cyanohydrin products. Selective reduction and hydrolysis of the CN group to an aldehyde completes the conversion of the triose d-glyceraldehyde to the pair of aldotetroses having a new chiral carbon...

Phosphatidyl Amine

Line models of some phospholipids. If R hydrogen, the compound is the phosphatidic acid as indicated. If the polar moieties shown below are substituted at R, the compound is the corresponding phosphatidyl-R i.e., if R is choline, the compound is phosphatidylcholine . When one of the acyl groups of a glycer-olphospholipid is removed, a phospholipid with a single hydrocarbon chain is formed this is called a lyso compound. Lysophos-pholipids are detergents because of their strong...

Cyclic and Conformational Structures

Aldoses and ketoses are more stable in their five- or six-membered cyclic hemiacetal form than in acyclic form. Cyclization of an aldose tablf. 1-1 Abbreviated Names for Some Common Carbohydrates tablf. 1-1 Abbreviated Names for Some Common Carbohydrates 'Abbreviations for di-, oligo-, and polysaccharides often add d- or L- to indicate the enantiomeric form, p or f to indicate the pyranose or furanose ring form, a- or p- to indicate the stereochemistry of the glycosidic linkage, and carbon...

The Maillard Reaction of Reducing Sugars with Amines

Aldoses and ketoses react with aliphatic primary and secondary amines including amino acids and proteins to form V-glyco-sides, which readily dehydrate to the respective Schiff base by the Maillard reaction, as shown in Figure 1-7 reactions i and ii . The aldose Schiff base spontaneously undergoes an Amadori rearrangement at C-l and C-2, giving a substituted 1-amino-l-deoxyketose reaction iii a ketose Schiff base will rearrange to a substituted 2-amino-2-deoxyal-dose. These sugar amines undergo...

Handbook Of Food Safety By J B Bernan

Triolein Packing

Absorption of the saturated fatty acid in the sn 3 position X refers to the chain length of 1,2 dioleoyl, 3 acyl-sn-glycerols the OOX series . OSO is 1-oleoyl, 2-steroyl, 3-oleoyl-glycerol. As the chain lengthens from 16 to 24 carbons, there is a sharp decline in the absorption of the saturated fatty acid. Oleate absorption was greater than 90 for all of the triacylglycerols. Based on data of Redgrave, T.G., Kodali, D. R. and Small, D. M. 11988 , The effect of triacyl-sn-glycerol...

Sharon Akabas PhD

Adjunct Assistant Professor, Institute of Human Nutrition and Teachers College, Columbia University, New York, New York Professor, Department of Pediatric Dentistry, University of North Carolina, Chapel Hill, North Carolina Associate Professor, School of Family and Consumer Services, The University of Southern Mississippi, Hattiesburg, Mississippi Associate Professor of Nutritional Medicine, Columbia University College of Physicians and Surgeons, New York, New York Instructor, Biomedical...

Structure and Properties of Lipids

Lipids and Their Functions The Chemical Classes of Lipids Hydrocarbons Substituted Hydrocarbons Waxes, Esters, and Ethers Acylglycerols and Fats Glycerophospholipids Sphingolipids Steroids The General Properties of Lipids Packing of Lipids in the Solid State The Liquid Crystalline State of Lipids The Liquid State Melts, Solutions, and Suspensions Determinants of Lipid Melting Surface Behavior of Lipids at the Water Interface Lipid Classification Based on Physical Interaction with Water...