Biochemistry Chapter 16
how many possible epimers of D-erythose exist
2 there are 4 carbons in d-erythrose. Carbons 2 and 3 are stereo centers. Inverting the positions of the -OH and -H on each of these carbons in D-erythose will produce an epimer of D-erythrose. Thus there are 2 possible epimers
Match the properties on the left with the polysaccharides on the right.
Chitin CONTAINS N-ACETYL-BETA-D-GLYCOSAMINE MONOMERS and. Cellulose CONTAINS BETA-D-GLUCOSE MONOMERS and OCCURS IN PLANTS Both Cellulose and Chitin uses BETA(1-->4) GLYCOSIDIC LINKAGE BETWEEN MONOMERS
Which of the following are epimers of D-glucose
D-mannose and D-allose Two epimers differ only at one chiral carbon. Thus, for D-glucose, there are three possible D-sugars that are epimers: D-mannose, D-allose, and D-galactose. There is only one possible L-sugar: L-idose. All other sugars either have too few or too many carbons or they have more than one chiral carbon with a different arrangement of -OH and -H groups as compared to D-glucose.
Match the carbohydrates on the left with their aldose/ketose pair carbohydrate on the right
D-ribulose - no match Dihydroxyacetone - Glyceraldehyde D-erythose - Derythulose D-xylulose - D-xylose The pairings of aldoses and ketoses require 1) the same numbers of carbons in each member of a pair and 2) the same pattern of hydroxyls from higher numbered carbons to lower numbered carbons. The latter requirement means that four-carbon and longer monosaccharides will have one ketosaccharide for two aldosaccharides as possible pairs. For example, D-erythrulose, a 4-carbon keto sugar, has its -OH group to the right on carbon 3 in a Fischer projection. This -OH group is drawn to the right in a Fischer projection. Both D-erythrose and D-threose, the two D-isomer 4-carbon sugars, have this same -OH conformation, so either one would make a suitable aldehyde partner in the aldose/ketose pair for D-erythrulose.
Match the properties on the left with the polysaccharides on the right.
Glycogen IS PRODUCED PRIMARLY IN ANIMALS Both glycogen and starch CONTAINS ALPHA-D-GLUCOSE MONOMERS Starch IS PRODUCED PRIMARILY IN PLANTS Neither glycogen or starch CONTAINS N-ACEYTL-BETA-D-GLUCOSAMINE MONOMERS.
Vitamin C and cyclic sugars share some structural similarities. Is vitamin C more or less susceptible to air oxidation than a cyclic sugar? why?
Less Susceptible the cyclic ester lactone ring of Vitamin C is different from the cyclic hemiacetal of a structurally similar sugar in that it has a greater susceptibility to oxidation.
match the properties on the left with the carbohydrates on the right
Neither sucrose nor lactose are MONOSACCHARIDES Lactose CONTAINS GALACTOSE Both Sucrose and Lactose CONTAIN GLUCOSE Lactose CONTAINS BETA-1,4 LINKAGE Both Sucrose and Lactose ARE DISACCHARIDE Sucrose CONTAINS FRUCTOSE Neither sucrose nor lactose CONTAIN A RIBOSE
Two sugars are epimers of each other. Is it possible to convert one to the other without breaking covalent bonds? Why?
No, Rotation around bonds will not alter the chirality of a stereocenter. thus only breaking the of a bond, followed by rotation, and then followed by bond reformation can convert a stereo center to its reversed conformation, as is found in the epimer of a particular chiral molecule.
Difference between furganose and pyranose
The pyranose form of a monosaccharide is a six-membered ring containing one oxygen atom
Of the following, which are characteristics of a reducing sugar?
The sugar readily acts as a reducing agent The sugar contains an aldehyde group
How many chiral centers are there in the open form of ribose? how many chiral centers are there in the closed form of ribose?
There are 5 carbons in ribose. Carbons 2, 3, and 4 all are stereocenters in the open form. Cyclizing ribose will involve an attack on carbon 1 (the aldehyde carbon) by the alcohol on carbon 4. Carbons 2, 3, and 4 will retain their chirality, but now carbon 1 will also have a stereocenter, so the cyclic form will have 4 chiral centers.
