Intro to Carbohydrates

Question 1

glycans (carbohydrates) have the following basic compositions:

Answer 1

(CHO2O)n or. H-C-OH

Question 2

Monosaccharides

Answer 2

•simple sugars with multiple OH groups.
•based on number of carbons (3,4,5,6) a monosaccharide is a triose, tetrose, pentose or hexose.

Question 3

Disaccharides

Answer 3

•2 monosaccharides covalently linked

Question 4

Oligosaccharides

Answer 4

•a few monosaccharides covalently linked.

Question 5

Polysaccharides

Answer 5

•polymers consisting of chains of monosaccharide or disaccharide units.

Question 6

Monosaccharides
➡️ Aldoses
➡️ Ketoses

Answer 6

➡️ Aldoses : (e.g., glucose) have an aldehyde group at one end

➡️ Ketoses : (e.g., fructose) have a keto group, usually at C2

Question 7

D vs L Designation

Answer 7

D & L designations are based on the configuration about the single asymmetric C in glyceraldehyde.

Question 8

Fischer Prjections

Answer 8

staraight lines connecting molecules

Question 9

SUGAR NOMENCLATURE

Answer 9

•for sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group.

•most naturally occurring sugars are D isomers.

•D & L sugars are mirror images of one another

•have the same name, e.g., D-glucose & L-glucose

•other stereoisomers have unique names, e.g., glucose, mannose, galactose, etc.

• the number of stereoisomers is 2n, where n is the number of asymmetric centers

•the 6-C aldoses have 4 asymmetric centers. Thus there are 16 stereoisomers (8 D-sugars and 8 L-sugars).

Question 10

HEMIACETAL & HEMIKETAL FORMATION

Answer 10

•An aldehyde can react to form a hemiacetal.

•A ketone can react with an alcohol to form a hemiketal.

Question 11

Pentoses and hexoses

Answer 11

can cyclize as the ketone or aldehyde reacts with a distal OH.

Question 12

Glucose forms an _______ hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member pyranose ring, named after pyran.

Answer 12

intra-molecular

Question 13

representations of cyclic sugars are called: _____ _______

Answer 13

Haworth projections.

Question 14

Fructose forms either:

Answer 14

• a 6-member pyranose ring, by reaction of the C2 keto group with the OH on C6, or
•a 5-member furanose ring, by reaction of the C2 keto group with the OH on C5

Question 15

Cyclization of glucose produces a new asymmetric center at C1. The 2 stereoisomers are called: _____, ___ & __

Answer 15

anomers, A & B

Question 16

Haworth projections represent the cyclic sugars as having essentially planar rings, with OH at anomeric C1:

a (OH ____ the ring)
B (OH ____ the ring)

Answer 16

a (OH BELOW the ring)
B (OH ABOVE the ring)

Question 17

It assumes a “chair” or “boat” configuration, because of the tertrahedral nature of carbon bonds, depends on the sugar.

Answer 17

pyranose sugars

Question 18

the ______ configuration of glycopyranose ring is more accurately represented than the Haworth projection.

Answer 18

The chair configuration

Question 19

SUGAR DERIVATIVES

Answer 19

• amino sugar- an amino group substitutes for a hydroxyl.
e.g., glucosamine

• the amino group may be acetylated, as in N-acetylglucosamine.

Question 20

N-acetylneuraminate also known as ______

Answer 20

sialic acid

Question 21

sialic acid is often found as a ______ _____ of oligosaccharides chains of glycoproteins.

Answer 21

terminal residue

Question 22

Sialic acid imparts negative charge to _______, because it’s carboxyl group tends to dissociate a proton at physiological pH,

Answer 22

glycoproteins

Question 23

GLYCOSIDIC BONDS

Answer 23

•the anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, splitting out water to form a glycosidic bond:

e.g., methanol reacts with the anomeric OH on glucose to form methyl glucoside (methyl-glycopyranose)