Monosaccharides and Disaccharides Flashcards
what is the difference between a ketose and an aldose sugar
If the carbonyl group is at an end of the carbon chain (that is, in an aldehyde group) the monosaccharide is an aldose; if the carbonyl group is at any other position (in a ketone group) the monosaccharide is a ketose
what are the two simplest monosaccharides
two three-carbon trioses: glyceraldehyde, an aldotriose, and dihydroxyacetone, a ketotriose
what are the most common monosaccarides in nature
The hexoses, which include the aldohexose D-glucose and the ketohexose D-fructose
Monosaccharides Have __________ Centers
Asymmetric
All the monosaccharides except ____________ contain one or more ____________ carbon atoms and thus occur in __________________
dihydroxyacetone
asymmetric (chiral)
optically active isomeric forms
what is the simplest aldose and describe its structure
glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers
what is the relationship bween chiral center and stereoisomers
a molecule with n chiral centers can have 2n stereoisomers
what isomers are most of the hexoses of living organisms
D isomers
When the hydroxyl group on the reference carbon is on the______ in the projection formula, the sugar is the D isomer; when on the _____, it is the L isomer
right
left
what is the structure of common monosaccharides
Cyclic Structures
how do aldotetroses and monosaccharides with 5+ carbon atoms form a cyclic structure
carbonyl group forms a covalent bond with the oxygen of a hydroxyl group along the chain
The formation of ring structures in monosaccahrides is the result of
reaction between alcohols and aldehydes or ketones to form derivatives called hemiacetals or hemiketals
what are anomers
Isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom
what is the anomeric carbon
hemiacetal (or carbonyl) carbon atom
what is the interconversion of the two cyclic forms of D-glucose called
mutarotation
what are the two cyclic forms of D-glucose
alpha D pyranose and beta D pyranose
why are the six membered ring compounds referred to as pyranose
because the resemble a 6 membered ring compound called pyran
what are furanoses
Aldohexoses existing in cyclic forms having fivemembered rings
which predominates in aldohexose solutions, aldopyranose or aldofuranose ring, and which one is more stable
aldopyranose
explain the reducing ability of monosaccharides
Monosaccharides can be oxidized by relatively mild oxidizing agents such as ferric (Fe+3) or cupric (Cu+2) ion. The carbonyl carbon is oxidized to a carboxyl group
what is a sensitive method of measuring blood glucose levels
employ an enzyme, glucose oxidase
how is a disaccharide formed
consist of two monosaccharides joined covalently by an O-glycosidic bond, which is formed when a hydroxyl group of one sugar reacts with the anomeric carbon of the other
The oxidation of a sugar’s anomeric carbon by cupric or ferric ion occurs only with the_______ which exists in equilibrium with the____________-
linear form
cyclic form
how does the disacchraide become a non-reducing sugar
When the anomeric carbon is involved in a glycosidic bond, that sugar residue cannot take the linear form and therefore becomes a nonreducing sugar
what is the reducing end of a disaccharide or polysaccharide
the end of a chain with a free anomeric carbon (one not involved in a glycosidic bond)
what are glycosidic bonds hydrolyed by and also resist cleavage by
acid
base
so disaccharides can form free mono when boiled with diulte acids
what does maltose contain
two D-glucose residues joined by a glycosidic linkage between C-1 (the anomeric carbon) of one glucose residue and C-4 of the other
why is maltose a reudcing sugar
Because the disaccharide retains a free anomeric carbon
what is the configuration of the anomeric carbon atom in the glycosidic linkage of maltose
α (alpha)
what does lactose yield in hydrolysis
D-galactose and D-glucose on hydrolysis
is lactose a reducing or non-reducing disacchride and what is the reason
it is a reducing disaccharide because the anomeric carbon of the glucose residue is available for oxidation
what is the abbreviated name of lactose
Gal (β1→4) Glc
what does sucrose contain
glucose and fructose
why is sucrose a non-reducing sugar
it contains no free anomeric carbon atom; the anomeric carbons of both monosaccharide units are involved in the glycosidic bond
what is the abbreviated name of trehalose
Glc(α1↔1α)Glc
what is trehalose composed of and is it a reducing or non-reducing sugar
D-glucose
nonreducing sugar
what is the function of trehalose in nature
is a major constituent of the circulating fluid (hemolymph) of insects, serving as an energy-storage compound
