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Chapter 25: Problem 44

Propose structural formulas for the following polysaccharides. (a) Alginic acid, isolated from seaweed, is used as a thickening agent in ice creatn and other foods. Alginic acid is a polymer of D-mannuronic acid in the pyranose form joined by \(\beta-1,4\)-glycosidic bonds. (b) Pectic acid is the main component of pectin, which is responsible for the formation of jellies from fruits and berries. Pectic acid is a polymer of D-galacturonic acid in the pyranose form joined by \(a-1,4\)-glycosidic bonds. O=CC(O)C(O)C(O)C(O)C(=O)O O=CC(O)C(O)C(O)C(O)C(=O)O D-Mannuronic acid D. Galacturonic acid

Short Answer

Expert verified
Answer: Alginic acid is a polymer of D-mannuronic acid in the pyranose form connected by β-1,4-glycosidic bonds, while pectic acid is a polymer of D-galacturonic acid in the pyranose form connected by α-1,4-glycosidic bonds.

Step by step solution

01

Identify the monomers and glycosidic bonds

First, we need to identify the monomers and glycosidic bonds involved in the formation of the polysaccharides in question. For alginic acid, we are given that it is a polymer of D-mannuronic acid in the pyranose form joined by β-1,4-glycosidic bonds. For pectic acid, it is a polymer of D-galacturonic acid in the pyranose form joined by α-1,4-glycosidic bonds.
02

Understand the pyranose form and glycosidic bonds

The pyranose form of a monosaccharide is a six-membered ring structure, with five carbons and one oxygen within the ring. The glycosidic bond is the linkage between two monomers in a polysaccharide, joining the anomeric carbon of one monomer to a hydroxyl group on another monomer. In this case, for alginic acid, the bond is β-1,4, meaning that it is a β-linkage between the first and fourth carbons in the pyranose ring. For pectic acid, the glycosidic bond is α-1,4, meaning it is an α-linkage between the first and fourth carbons.
03

Draw the D-mannuronic acid monomer structure

D-mannuronic acid has the following skeletal structure with an aldehyde group at carbon 1 and carboxylic acid groups at carbon 6: O=CC(O)C(O)C(O)C(O)C(=O)O From the given structure, the pyranose form of D-mannuronic acid can be drawn: a six-membered ring with the anomeric carbon (carbon 1) being a part of the ring along with the oxygen.
04

Draw the D-galacturonic acid monomer structure

D-galacturonic acid, similar to D-mannuronic acid, also has an aldehyde group at carbon 1 and a carboxylic acid group at carbon 6: O=CC(O)C(O)C(O)C(O)C(=O)O The pyranose structure of D-galacturonic acid can be drawn similar to D-mannuronic acid, with a six-membered ring containing one oxygen and carbons 1 through 6 in the ring.
05

Show the β-1,4 linkage in alginic acid

To draw the structural formula of alginic acid, we need to show how the β-1,4-glycosidic linkage forms between the monomers of D-mannuronic acid. This bond is formed between the hydroxyl group on the first carbon of one monomer and the oxygen on the fourth carbon of another monomer.
06

Show the α-1,4 linkage in pectic acid

Similarly, for the structural formula of pectic acid, we need to show the α-1,4-glycosidic bond connecting the hydroxyl group on carbon 1 of one D-galacturonic acid monomer with the oxygen on carbon 4 of another monomer. By following these steps, you can draw the structural formulas for alginic acid and pectic acid, showing the pyranose form of the monomers and the glycosidic linkages between them.

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Most popular questions from this chapter

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