Chapter 7 part 1 (monosaccharides)

anomers

Isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom

reducing sugars

-Glucose and other sugars capable of reducing cupric ion are -Cupric ion oxidizes glucose and certain other sugars to a complex mixture of carboxylic acids. -semi-quantitative test for the presence of reducing sugar that for many years was used to detect and measure elevated glucose levels in people with diabetes mellitus.

furanose

-Ketohexoses (such as fructose) also occur as cyclic compounds with α and β anomeric forms. -hydroxyl group at C-5 (or C-6) reacts with the keto group at C-2 -ring containing a hemiketal linkage

L isomer

-OH group is on the left

D isomer

-OH group is on the right -Most of the hexoses of living organisms are D isomers.

uronic acid

-Oxidation of the carbon at the other end of the carbon chain—C-6 of glucose, galactose, or mannose—forms ___ -Example: glucuronic, galacturonic, or mannuronic acid

pyranoses

-Six-membered ring compounds because they resemble the six-membered ring compound pyran. -systematic names for the two ring forms of D-glucose are therefore α-D-glucopyranose and β-D-glucopyranose.

mutarotation

-The alpha and beta anomers of D-glucose interconvert in aqueous solution by a process -one ring form (say, the alpha anomer) opens briefly into the linear form, then closes again to produce the beta anomer -solution of alpha-D-glucose and a solution of beta-D-glucose eventually form identical equilibrium mixtures having identical optical properties -This mixture consists of about one-third alpha-D-glucose, two-thirds beat-D-glucose, and very small amounts of the linear and five-membered ring (glucofuranose) forms.

epimers

-Two sugars that differ only in the configuration around one carbon atom -D-glucose and D-mannose, which differ only in the stereochemistry at C-2, are epimers, as are D-glucose and D-galactose (which differ at C-4)

sialic acids

-a family of sugars with the same nine-carbon backbone -One of them, N-acetylneuraminic acid , occur in many glycoproteins and glycolipids on animal cell surfaces, providing sites of recognition by other cells or extracellular carbohydrate- binding proteins. -ionized at pH 7 -named as the carboxylates— glucuronate, galacturonate, and so forth

monosaccharides

-aldehydes or ketones two or more hydroxyle groups -the six-carbon monosaccharides glucose and fructose have five hydroxyle groups. -form chiral centers, leading to many stereoisomers found in nature which is biological significant because enzymes act on sugars are strictly stereospecific.

Asymmetric center

-all monosaccharides expect dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and occur in active isomers forms

Condensation of phosphoric acid with one of the hydroxyl groups of a sugar forms a phosphate ester

-as in glucose 6-phosphate, the first metabolite in the pathway by which most organisms oxidize glucose for energy -stable at neutral ph and bear a negative charge -trap sugar inside the cell

anomeric carbon

-chiral carbonyl carbon in cyclic form -carbon is bonded to both the ring O and a hydroxyl group

describe monosaccharides

-colorless, crystalline solids that are freely soluble in water but insoluble in nonpolar solvents. -have sweet taste -backbones of common ones are unbranded carbon chain linked by single bonds

Organisms Contain a Variety of Hexose Derivatives

-glucosamine, galactosamine, and mannosamine, the hydroxyl at C-2 of the parent compound is replaced with an amino group -The amino group is commonly condensed with acetic acid, as in N-acetylglucosamine -glucosamine derivative is part of many structural polymers like bacterial cell wall -L-Fucose is found in the complex oligosaccharide components of glycoproteins and glycolipids; L-rhamnose is found in plant polysaccharides.

Carbohydrates polymers

-glycans -structural and protective elements in the cell walls of baterm-9cteria and plants and in the connective tissues of animals -Other carbohydrate polymers lubricate skeletal joints and participate in recognition and adhesion between cells

glyceraldehyde

-have isomer -the D and L isomer -In Fischer projection formulas, horizontal bonds project out of the plane of the paper, toward the reader; vertical bonds project behind the plane of the paper, away from the reader

the common monosaccharides have cyclic structures

-in aqueous solution, with five or more carbon occur as syclic -carbonyle group formed covalent bond with oxygen of hydroxyle group along with the chain

hexoses,

-include the aldohexose D-glucose and the ketohexose D-fructose -most common monosaccharides in nature- products of photosynthesis and key intermediates in the central energy-yielding reaction

enantiomers

-isomers that are mirror images of each other -simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom)

Three major size classes of carbohydrates

-monosaccharides -oligosaccharides, -polysaccharides -saccharide= sugar

Carbohydrates

-most abundant -sugar and starch; a dietary staple in most parts of the world -oxidation of carbohydrates is the central energy-yielding pathway in most non-photosynthetic cells -polyhydroxy aldehydes or ketones, or substances that yield such compounds on hydrolysis. -formula (CH2O)n; some also contain nitrogen, phosphorus, or sulfur

monosaccharied in open-chain form

-one of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group; each of the other carbon atoms has a hydroxyl group

Monosaccharides Are Reducing Agents

-oxidized by relatively mild oxidizing agents such as cupric (Cu2+) ion -carbonyl carbon is oxidized to a carboxyl group

hemiacetals or hemiketals

-ring structures is the result of a general reaction between alcohols and aldehydes or ketones -Addition of the second molecule of alcohol produces the full acetal or ketal (Fig. 7-5), and the bond formed is a glycosidic linkage. -two molecules that react are both monosaccharides, the acetal or ketal formed is a disaccharide.

Oligosaccharides

-short chains of monosaccharide units, or residues, joined by characteristic linkages called glycosidic bonds.

Monosaccharides

-simple sugars, consist of a single polyhydroxy aldehyde or ketone unit. -in six-carbon sugar D-glucose, sometimes referred to as dextrose -four or more carbons tend to have cyclic structures

Example of L isomers

-some sugars occur naturally in their L form -Ex: L-arabinos -some sugar derivatives that are common components of glycoconjugates

polysaccharides

-sugar polymers containing more than 20 or so monosaccharide units; some have hundreds or thousands of units. ex: cellulose, are linear chains; others, such as glycogen, are branched -recurring units of D-glucose, but differ in type of glycosidic linkage and consequently have strikingly different properties and biological roles

Disaccharides

-two monosaccharides joined together -sucrose consists of the six carbon sugars D-glucose and D-fructose -All common monosaccharides and disaccharides have names ending with the suffix "-ose."

stereospecific

-typically preferring one stereoisomer to another by three or more orders of magnitude, as reflected in Km values or binding constants

Haworth perspective formulas

A method for representing cyclic chemical structures so as to define the configuration of each substituent group; commonly used for representing sugars.

Fischer projection formulas

A method for representing molecules that shows the configuration of groups around chiral centers; also known as projection formulas. -three dimensional sugar structures on paper

glycoconjugates

Complex carbohydrate polymers covalently attached to proteins or lipids act as signals that determine the intracellular destination or metabolic fate of these hybrid molecules

Monosaccharides : Some examples of Aldoses

D-erythrose D-ribose D-galactose D-glucose

Monosaccharides : Some examples of Ketoses

D-erythrulose D-ribulose D-Fructose

aldose

If the carbonyl group is at an end of the carbon chain (that is, in an aldehyde group) the monosaccharide is a _____

eight D-aldohexoses, which differ in the stereochemistry at C-2, C-3, or C-4,

has its own name: D-glucose, D-galactose, D-mannose, and so forth -Configuration of the chiral carbon in glyceraldehyde and the chiral carbon most distal from the carbonyl group in any monosaccharide should be same.

Ketose

if the carbonyl group is at any other position (in a ketone group) the monosaccharide is a ______

-Both aldonic and uronic acids form stable intramolecular esters called

lactones

aldonic acids

oxidation of aldolases during open-chain aldehyde form

Monosaccharides with four, five, six, and seven carbon atoms in their backbones are called

tetroses, pentoses, hexoses, and heptoses