Define the following vocabulary terms.
a. Reducing sugar
b. Non-reducing sugar
c. Aldose
d. Ketose
e. Monosaccharide
f. Disaccharide
g. Dichotomous Key
The correct answer and explanation is:
a. Reducing Sugar
A reducing sugar is any sugar that has a free aldehyde or ketone group, which can donate electrons to reduce another substance. This ability to reduce is what characterizes reducing sugars. Monosaccharides like glucose, fructose, and galactose, as well as some disaccharides like maltose and lactose, are considered reducing sugars because they possess a free aldehyde or ketone group. This feature allows reducing sugars to react with certain chemicals, such as Benedict’s solution, causing a color change.
b. Non-reducing Sugar
Non-reducing sugars are carbohydrates that do not have a free aldehyde or ketone group, meaning they cannot act as reducing agents. An example is sucrose, a disaccharide made up of glucose and fructose. In sucrose, the aldehyde group of glucose and the hydroxyl group of fructose are involved in a glycosidic bond, preventing them from participating in reduction reactions. Non-reducing sugars do not show a color change when treated with Benedict’s solution unless they are first hydrolyzed into their constituent monosaccharides.
c. Aldose
An aldose is a type of monosaccharide that contains an aldehyde group (-CHO) at the end of the molecule. The aldehyde group is what differentiates aldoses from ketoses. Common examples of aldoses include glucose, galactose, and ribose. Aldoses typically have the general formula CnH2nOnC_nH_{2n}O_n, where n is the number of carbon atoms in the molecule.
d. Ketose
A ketose is a type of monosaccharide that contains a ketone group (-C=O) within the molecule, as opposed to at the end, like in aldoses. Ketoses are typically found in sugars such as fructose and ribulose. Their structure includes a carbonyl group attached to a carbon atom that is not at the end of the molecule. Ketoses, like aldoses, also follow the general formula CnH2nOnC_nH_{2n}O_n.
e. Monosaccharide
A monosaccharide is the simplest form of carbohydrate, consisting of a single sugar unit. Monosaccharides are the building blocks of more complex carbohydrates like disaccharides and polysaccharides. Examples of monosaccharides include glucose, fructose, and galactose. They are typically classified based on the number of carbon atoms (e.g., trioses, pentoses, hexoses) and whether they are aldoses or ketoses.
f. Disaccharide
A disaccharide is a carbohydrate formed by two monosaccharides linked by a glycosidic bond. The most common disaccharides include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose). Disaccharides can be broken down into their monosaccharide components through hydrolysis, a process often catalyzed by enzymes.
g. Dichotomous Key
A dichotomous key is a tool used to identify organisms or objects based on a series of paired, contrasting statements. Each pair leads the user to the next set of choices until the organism or object can be identified. Dichotomous keys are widely used in fields like biology and taxonomy to classify species based on observable traits.
Sources:
- Nelson, D.L., Cox, M.M. Lehninger Principles of Biochemistry. 7th ed. W.H. Freeman and Company, 2017.
- Berg, J.M., Tymoczko, J.L., Gatto, G.J. Stryer, L. Biochemistry. 8th ed. W.H. Freeman, 2015.