Monosaccharides and Disaccharides

Question 1

what is the difference between a ketose and an aldose sugar

Answer 1

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

Question 2

what are the two simplest monosaccharides

Answer 2

two three-carbon trioses: glyceraldehyde, an aldotriose, and dihydroxyacetone, a ketotriose

Question 3

what are the most common monosaccarides in nature

Answer 3

The hexoses, which include the aldohexose D-glucose and the ketohexose D-fructose

Question 4

Monosaccharides Have __________ Centers

Answer 4

Asymmetric

Question 5

All the monosaccharides except ____________ contain one or more ____________ carbon atoms and thus occur in __________________

Answer 5

dihydroxyacetone
asymmetric (chiral)
optically active isomeric forms

Question 6

what is the simplest aldose and describe its structure

Answer 6

glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers

Question 7

what is the relationship bween chiral center and stereoisomers

Answer 7

a molecule with n chiral centers can have 2n stereoisomers

Question 8

what isomers are most of the hexoses of living organisms

Answer 8

D isomers

Question 9

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

Answer 9

right

left

Question 10

what is the structure of common monosaccharides

Answer 10

Cyclic Structures

Question 11

how do aldotetroses and monosaccharides with 5+ carbon atoms form a cyclic structure

Answer 11

carbonyl group forms a covalent bond with the oxygen of a hydroxyl group along the chain

Question 12

The formation of ring structures in monosaccahrides is the result of

Answer 12

reaction between alcohols and aldehydes or ketones to form derivatives called hemiacetals or hemiketals

Question 13

what are anomers

Answer 13

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

Question 14

what is the anomeric carbon

Answer 14

hemiacetal (or carbonyl) carbon atom

Question 15

what is the interconversion of the two cyclic forms of D-glucose called

Answer 15

mutarotation

Question 16

what are the two cyclic forms of D-glucose

Answer 16

alpha D pyranose and beta D pyranose

Question 17

why are the six membered ring compounds referred to as pyranose

Answer 17

because the resemble a 6 membered ring compound called pyran

Question 18

what are furanoses

Answer 18

Aldohexoses existing in cyclic forms having fivemembered rings

Question 19

which predominates in aldohexose solutions, aldopyranose or aldofuranose ring, and which one is more stable

Answer 19

aldopyranose

Question 20

explain the reducing ability of monosaccharides

Answer 20

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

Question 21

what is a sensitive method of measuring blood glucose levels

Answer 21

employ an enzyme, glucose oxidase

Question 22

how is a disaccharide formed

Answer 22

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

Question 23

The oxidation of a sugar’s anomeric carbon by cupric or ferric ion occurs only with the_______ which exists in equilibrium with the____________-

Answer 23

linear form

cyclic form

Question 24

how does the disacchraide become a non-reducing sugar

Answer 24

When the anomeric carbon is involved in a glycosidic bond, that sugar residue cannot take the linear form and therefore becomes a nonreducing sugar

Question 25

what is the reducing end of a disaccharide or polysaccharide

Answer 25

the end of a chain with a free anomeric carbon (one not involved in a glycosidic bond)

Question 26

what are glycosidic bonds hydrolyed by and also resist cleavage by

Answer 26

acid
base
so disaccharides can form free mono when boiled with diulte acids

Question 27

what does maltose contain

Answer 27

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

Question 28

why is maltose a reudcing sugar

Answer 28

Because the disaccharide retains a free anomeric carbon

Question 29

what is the configuration of the anomeric carbon atom in the glycosidic linkage of maltose

Answer 29

α (alpha)

Question 30

what does lactose yield in hydrolysis

Answer 30

D-galactose and D-glucose on hydrolysis

Question 31

is lactose a reducing or non-reducing disacchride and what is the reason

Answer 31

it is a reducing disaccharide because the anomeric carbon of the glucose residue is available for oxidation

Question 32

what is the abbreviated name of lactose

Answer 32

Gal (β1→4) Glc

Question 33

what does sucrose contain

Answer 33

glucose and fructose

Question 34

why is sucrose a non-reducing sugar

Answer 34

it contains no free anomeric carbon atom; the anomeric carbons of both monosaccharide units are involved in the glycosidic bond

Question 35

what is the abbreviated name of trehalose

Answer 35

Glc(α1↔1α)Glc

Question 36

what is trehalose composed of and is it a reducing or non-reducing sugar

Answer 36

D-glucose

nonreducing sugar

Question 37

what is the function of trehalose in nature

Answer 37

is a major constituent of the circulating fluid (hemolymph) of insects, serving as an energy-storage compound