CHEMISTRY GLOSSARY

monosaccharide    →   monosaharid

Monosaccharides are carbohydrates, with the general formula C_n(H₂O)_n, that cannot be decomposed to a simpler carbohydrates by hydrolysis.

Depending on whether the molecule contains an aldehyde group (-CHO) or a ketone group (-CO-) monosaccharide can be a polyhydroxy aldehyde (aldose) or a polyhydroxy ketone (ketose). These aldehyde and ketone groups confer reduction properties on monosaccharides. They are also classified according to the number of carbon atoms they contain: trioses have three carbon atoms, tetroses four, pentoses five, hexoses six, heptoses seven, etc. These two systems of classification are often combined. For example, a six-carbon polyhydroxy aldehyde such as D-glucose is an aldohexose, whereas a six-carbon polyhydroxy ketone such as D-fructose is a ketohexose.

The notations D and L are used to describe the configurations of carbohydrates. In Fischer projections of monosaccharides, the carbonyl group is always placed on top (in the case of aldoses) or as close to the top as possible (in the case of ketoses). If the OH group attached to the bottom-most asymmetric carbon (the carbon that is second from the bottom) is on the right, then the compound is a D-sugar. If the OH group is on the left, then the compound is an L-sugar. Almost all sugars found in nature are D-sugars.

Monosaccharides can exist as either straight-chain or ring-shaped molecules. During the conversion from straight-chain form to cyclic form, the carbon atom containing the carbonyl oxygen, called the anomeric carbon, becomes a chiral center with two possible configurations (anomers), α and β. When the stereochemistry of the first carbon matches the stereochemistry of the last stereogenic center the sugar is the α-anomer when they are opposite the sugar is the β-anomer.

starch    →   škrob

Starch (C₆H₁₀O5)_x is a polysaccharide used by plants to stockpile glucose molecules. It is the major component of flour, potatoes, rice, beans, corn, and peas. Starch is a mixture of two different polysaccharides: amylose (about 20 %), which is insoluble in cold water, and amylopectin (about 80 %), which is soluble in cold water. Amylose is composed of unbranched chains of D-glucose units joined by α(1→4)-glycosidic linkages. Unlike amylose, which are linear polymers, amylopectin contains α(1→6)-glycoside branches approximately every 25 glucose units.

Starch digestion begins in the mouth via the action of amylase, a digestive enzyme present in saliva. The process is completed in the small intestine by the pancreatic amylase. The final products of starch digestion, glucose molecules, are absorbed into the intestinal bloodstream and transported to the liver. Like most enzymes, glycosidases are highly selective in their action. They hydrolyze only the α-glycoside links in starch and leave the β-glycoside links in cellulose untouched. Starch is important food stuff and is used in adhesives, and sizes, in laundering, pharmacy and medicine.

sucrose    →   saharoza

Sucrose (saccharose), or ordinary table sugar, is a disaccharide in which α-D-glucopyranose and β-D-fructofuranose are joined at their anomeric carbons by a glycosidic bond. There are no hemiacetals remaining in the sucrose and therefore sucrose is not a reducing sugar and does not exhibit mutarotation. Sugar is a white crystalline sweet compound found in many plants and extracted from sugar cane and sugar beet. It is used as a sweetening agent in food and drinks. If heated to 200 °C, sucrose becomes caramel. When sucrose is hydrolyzed it forms an equimolar mixture of glucose and fructose. This mixture of monosaccharides is called invert sugar. Honeybees have enzymes called invertases that catalyze the hydrolysis of sucrose. Honey, in fact, is primarily a mixture of glucose, fructose, and sucrose.

sugar    →   šećer

Sugar is any of a group of water-soluble carbohydrates of relatively low molecular weight and typically having a sweet taste. The group comprises mainly monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, lactose, maltose), and trisaccharides (raffinose). Many monosaccharides and disaccharides fairly commonly found in nature bear names reflecting the source from which they were first isolated. For example, glucose is also known as grape sugar, lactose as milk sugar, and maltose as malt sugar. In everyday usage, the name is often used to refer specifically to sucrose (table sugar, cane sugar, beet sugar).

Chitosan    →   Kitozan

Chitosan is a linear polysaccharide composed of randomly distributed N-acetyl D-glucosamine and D-glucosamine units. It can be easily derived from partial deacetylation of natural polymer chitin. At a minimum deacetylization level of 60 % (amount of free amino groups in the polymer) it is considered to be chitosan. Thanks to the amino groups of D-glucosamine, chitosan can be protonated and turned into polycation, which is one of the sources of unique properties of chitosan as biopolymer, like aqueous solubility, antibacterial properties, biodegradability with non-toxic residues and biocompatibility.

Chitin    →   Hitin

Chitin is a nitrogen-containing linear polysaccharide of ß(1->4) linked units of N-acetyl-ß-d-glucosamine. The structure of chitin is similar to cellulose except for the replacement hydroxyl group (-OH) at the carbon 2 with an acetyl amine group (–NH–CO–CH3). Chitin is the main component of the exoskeleton, or outer covering of insects, crustaceans, and arachnids. It is also found in the cell walls of certain fungi and algae. After cellulose, chitin is the second most abundant biopolymer in nature. It is insoluble in water, organic solvents, weak acids and lyes.