Carbohydrates Flashcards
What does it mean to describe a glycosidic bond as b-1,4-? To describe it as a-1,6-?
To say that it is a b-1,4-glycosidic bond means that the configuration at the anomeric carbon (carbon 1 in this problem) of the monosaccharide unit forming the glycosidic
bond is beta and that it is bonded to carbon 4 of the second monosaccharide unit. To say that it is an a-1,6-glycosidic bond means that the configuration at the anomeric carbon (carbon 1 in this problem) of the monosaccharide unit forming the glycosidic bond is alpha and that it is bonded to carbon 6 of the second monosaccharide unit.
What is an amino sugar? Name the three amino
sugars most commonly found in nature.
In an amino sugar, one or more OH groups are
replaced by NH2 groups. The three most abundant amino sugars in the biological world are D-glucosamine, D-galactosamine, and N-acetyl-D-glucosamine.
Define (a) pyranose and (b) furanose.
(a) A pyranose is a six-membered cyclic hemiacetal form of a monosaccharide.
(b) A furanose is a five-membered cyclic hemiacetal form of a monosaccharide.
In what way are chair conformations a more accurate representation of the molecular shapes of hexopyranoses than Haworth projections?
A Haworth projection shows the six-membered ring as a planar hexagon. In reality, the ring is puckered and its most stable conformation is a chair conformation with all bond angles approximately 109.5°.
What is the difference in structure between an
aldose and a ketose? Between an aldopentose and a ketopentose?
The carbonyl group in an aldose is an aldehyde. In ketose, it is a ketone.
Which carbon of an aldopentose determines
whether the pentose has a D or L configuration?
The D or L configuration in an aldopentose is determined by its configuration at carbon 4.
Are a-D-glucose and b-D-glucose anomers? Explain. Are they enantiomers? Explain.
Yes, they are anomers. No, they are not enantiomers; they are not mirror images. They differ in configuration only at carbon 1 and are diastereomers.
Define the terms glycoside and glycosidic bond.
A glycoside is a cyclic acetal of a monosaccharide.
A glycosidic bond is a bond from the anomeric carbon to the -OR group of the glycoside.
What does it mean to say that D- and L-glyceraldehyde are enantiomers?
To say that they are enantiomers means that they are nonsuperposable mirror images.
Do glycosides undergo mutarotation?
No, glycosides cannot undergo mutarotation because the anomeric carbon is not free to interconvert between a and b configurations via the open-chain aldehyde or ketone.
Hyaluronic acid acts as a lubricant in the synovial fluid of joints. In rheumatoid arthritis, inflammation breaks hyaluronic acid down into smaller molecules. Under these conditions, what happens to the lubricating power of the synovial fluid?
Its lubricating power decreases.
The specific rotation of a-D-glucose is 1112.2°.
What is the specific rotation of a-L-glucose?
The specific rotation of a-L-glucose is 2112.2°.
Starch can be separated into two principal polysaccharides, amylose, and amylopectin. What is the major difference in structure between the two?
The difference lies in the degree of chain branching.
Amylose is composed of unbranched chains, whereas amylopectin is a branched network with branches started by b-1,6-glycosidic bonds.
Name the three most abundant hexoses in the biological world. Which are aldohexoses, and which are ketohexoses?
The three most abundant hexoses in the biological world are D-glucose, D-galactose, and D-fructose. The first two are aldohexoses. The third is a 2-ketohexose.
What is the difference in structure between oligosaccharides and polysaccharides?
An oligosaccharide contains approximately six to ten monosaccharide units. A polysaccharide contains more—generally many more—than ten monosaccharide units.
