Human milk contains about 7. This sugar is one of the lowest ranking in terms of sweetness, being about one-sixth as sweet as sucrose. Lactose is produced commercially from whey, a by-product in the manufacture of cheese. It is important as an infant food and in the production of penicillin. Many adults and some children suffer from a deficiency of lactase. These individuals are said to be lactose intolerant because they cannot digest the lactose found in milk.
A more serious problem is the genetic disease galactosemia, which results from the absence of an enzyme needed to convert galactose to glucose. Certain bacteria can metabolize lactose, forming lactic acid as one of the products.
As a result, many adults experience a reduction in the ability to hydrolyze lactose to galactose and glucose in their small intestine. For some people the inability to synthesize sufficient enzyme increases with age. 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.
Disaccharides differ from other forms of carbohydrates, oligosaccharides, and polysaccharides , in the number of monosaccharide units that make them up. Disaccharides are made up of only two whereas oligosaccharides are made up of three to ten monosaccharides. Polysaccharides , as the name implies, contain several monosaccharide units. The chemical process of joining monosaccharide units is referred to as dehydration synthesis since it results in the release of water as a byproduct.
Disaccharides are formed by displacing a hydroxyl radical from one monosaccharide and a proton from the other monosaccharide and then causing the two monosaccharides to covalently link together. The detached hydroxyl radical and proton hydrogen ion , in turn, join and form a water molecule. Thus, one way of synthesizing a disaccharide is through the condensation of two monosaccharides. A disaccharide may be reverted to its monomeric monosaccharide components through hydrolysis with the help of the enzyme disaccharidases e.
While condensation reaction involves the elimination of water, hydrolysis utilizes a water molecule. A reducing disaccharide is a disaccharide in which the reducing sugar has a free hemiacetal unit that may serve as a reducing aldehyde group. Examples of reducing disaccharides are maltose and cellobiose. A non-reducing disaccharide , as its name implies, is a disaccharide that does not act as a reducing agent.
Both monosaccharides that make up the disaccharide do not have a free hemiacetal unit since they bond through an acetal linkage between their anomeric centers. Examples are sucrose and trehalose. There are several forms of disaccharides but the most common ones are sucrose , lactose , and maltose. These three are made up of two monosaccharides joined by a covalent bond. The general chemical formula is C 12 H 22 O Sucrose common table sugar is a disaccharide formed by the combination of glucose and fructose.
These two monosaccharides combine through a condensation reaction. They are linked through a glycosidic linkage between C-1 on the glycosyl unit and C-2 on the fructosyl unit. Sucrose is digested or broken down into its monosaccharide units through hydrolysis with the help of the enzyme, sucrase.
The bond that joins the two monosaccharides is broken, converting sucrose to glucose and fructose. Sucrose is extracted from plants, e. It is used as a sweetening agent in food and beverages. Lactose milk sugar is formed by the combination of glucose and galactose.
It has a chemical formula of C 12 H 22 O Maltose, or malt sugar, is a disaccharide formed by a dehydration reaction between two glucose molecules. The most common disaccharide is sucrose, or table sugar, which is composed of the monomers glucose and fructose. The chain may be branched or unbranched, and it may contain different types of monosaccharides.
Starch, glycogen, cellulose, and chitin are primary examples of polysaccharides. Plants are able to synthesize glucose, and the excess glucose is stored as starch in different plant parts, including roots and seeds. The starch in the seeds provides food for the embryo as it germinates while the starch that is consumed by humans is broken down by enzymes into smaller molecules, such as maltose and glucose.
The cells can then absorb the glucose. Glycogen is the storage form of glucose in humans and other vertebrates. It is made up of monomers of glucose. Glycogen is the animal equivalent of starch and is a highly branched molecule usually stored in liver and muscle cells. Whenever blood glucose levels decrease, glycogen is broken down to release glucose in a process known as glycogenolysis. Cellulose is the most abundant natural biopolymer. The cell wall of plants is mostly made of cellulose and provides structural support to the cell.
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. Carbohydrates are a major class of biological macromolecules that are an essential part of our diet and provide energy to the body. Biological macromolecules are large molecules that are necessary for life and are built from smaller organic molecules.
One of the OH groups is attached to the anomeric carbon the carbon that has 2 oxygens bonded to it. Here you see the formation of sucrose from the 6-membered form of glucose and the 5-membered form of fructose. Note that linear fructose has a ketone rather than an aldehyde group.
Which carbon in glucose and in fructose would be the carbonyl carbon in the linear form?
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