These are taken orally with dairy foods—or may be added to them directly—to assist in their digestion. Galactosemia is a condition in which one of the enzymes needed to convert galactose to glucose is missing.
Consequently, the blood galactose level is markedly elevated, and galactose is found in the urine. An infant with galactosemia experiences a lack of appetite, weight loss, diarrhea, and jaundice. The disease may result in impaired liver function, cataracts, mental retardation, and even death.
If galactosemia is recognized in early infancy, its effects can be prevented by the exclusion of milk and all other sources of galactose from the diet. As a child with galactosemia grows older, he or she usually develops an alternate pathway for metabolizing galactose, so the need to restrict milk is not permanent. The incidence of galactosemia in the United States is 1 in every 65, newborn babies.
Sucrose, probably the largest-selling pure organic compound in the world, is known as beet sugar , cane sugar , table sugar , or simply sugar. The dark brown liquid that remains after the recrystallization of sugar is sold as molasses. This linkage gives sucrose certain properties that are quite different from those of maltose and lactose.
Thus, sucrose is incapable of mutarotation and exists in only one form both in the solid state and in solution. In addition, sucrose does not undergo reactions that are typical of aldehydes and ketones. Therefore, sucrose is a nonreducing sugar. The hydrolysis of sucrose in dilute acid or through the action of the enzyme sucrase also known as invertase gives an equimolar mixture of glucose and fructose.
This mixture is referred to as invert sugar because it rotates plane-polarized light in the opposite direction than sucrose. The hydrolysis reaction has several practical applications. Sucrose readily recrystallizes from a solution, but invert sugar has a much greater tendency to remain in solution. In the manufacture of jelly and candy and in the canning of fruit, the recrystallization of sugar is undesirable. Therefore, conditions leading to the hydrolysis of sucrose are employed in these processes.
Moreover, because fructose is sweeter than sucrose, the hydrolysis adds to the sweetening effect. Several mass spectrometry-based methods have been applied to the discrimination of disaccharide isomers, but limited quantitative analyses have been reported. Three different types of disaccharide isomers were successfully relatively quantified in a binary mixture using the specific product ion pairs.
Finally, this method was utilized to identify and relatively quantify two disaccharide isomers in Medicago leaf maltose and sucrose without numerous preparation steps. In general, this method is a fast, effective, and robust method for rapid differentiation and quantitation of disaccharide isomers in complex medium.
Supplementary figures PDF. Such files may be downloaded by article for research use if there is a public use license linked to the relevant article, that license may permit other uses. View Author Information. Cite this: Anal. Article Views Altmetric -. Citations Therefore, sugars can exist as pairs of stereoisomers or enantiomers which are mirror images of one another. The center C-atom of glycerose is called an asymmetric C-atom because it can be rearranged in space to produce two different structures.
These differences do not affect the physical properties but can affect the biochemical properties due to changing the shape of the molecule. An L-isomer has the OH on the left of the center carbon:. To distinguish between the isomers, they are labeled L and D isomers. Each carbon atom is then numbered in order through the end of the chain. When numbering stereoisomers that have more than three carbon atoms we look at the position of the OH group on the penultimate or next to last carbon atom because this determines whether it is an L or D stereoisomer.
In this example we will look at the numbering of D-Glucose. First we must find the reactive end of the molecule and assign its carbon the number one. We then number the remaining carbons in order through the end of the chain.
In theory, in glucose, the position of the OH group on each of the asymmetric carbon atoms, numbers two, three, four, and five could be flipped, producing a distinct stereoisomer each time, for a total of 16 or 2 4 stereoisomers. However, not all of these actually exist in nature. For fructose, there are only three asymmetric carbons, so only 8 or 2 3 stereoisomers can be produced.
Only a few of the monosaccharides exist free in nature. Most of them are usually found as sugar units in polysaccharides or in more complex molecules. Monosaccharides are often called simple sugars, and are sub-divided according to the number of C-atoms. These compounds are important metabolic intermediates in the oxidation of glucose to produce energy.
Pentoses C 5 H 10 O 5 Three important pentoses are:. Every other glucose monomer in cellulose is flipped over, and the monomers are packed tightly as extended long chains. This gives cellulose its rigidity and high tensile strength—which is so important to plant cells. Because of the way the glucose subunits are joined, every glucose monomer is flipped relative to the next one resulting in a linear, fibrous structure.
Carbohydrates serve various functions in different animals. Arthropods have an outer skeleton, the exoskeleton, which protects their internal body parts. This exoskeleton is made of chitin, which is a polysaccharide-containing nitrogen. Chitin is also a major component of fungal cell walls. Privacy Policy. Skip to main content. Search for:. Carbohydrates Carbohydrate Molecules Carbohydrates are essential macromolecules that are classified into three subtypes: monosaccharides, disaccharides, and polysaccharides.
Learning Objectives Describe the structure of mono-, di-, and poly-saccharides. Key Takeaways Key Points Monosaccharides are simple sugars made up of three to seven carbons, and they can exist as a linear chain or as ring-shaped molecules. Glucose, galactose, and fructose are monosaccharide isomers, which means they all have the same chemical formula but differ structurally and chemically. Disaccharides form when two monosaccharides undergo a dehydration reaction a condensation reaction ; they are held together by a covalent bond.
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