Question

Sketch the straight-chain representations of the aldehyde sugar glucose and of the ketone sugar fructose. Circle the aldehyde or ketone functional group in your structures.

Short answer

The straight-chain representation of glucose is: O || C - H (C1, Aldehyde) | C - OH (C2) | C - OH (C3) | C - OH (C4) | C - OH (C5) | C - CH2OH (C6) The straight-chain representation of fructose is: CH2OH (C1) | C = O (C2, Ketone) | C - OH (C3) | C - OH (C4) | C - OH (C5) | C - CH2OH (C6) In both structures, the aldehyde and ketone functional groups are circled at Carbon 1 for glucose and Carbon 2 for fructose, respectively.

Step-by-step solution

Draw the straight-chain representation of glucose

To draw the straight-chain representation of glucose, we need to know its molecular formula, which is \(C_6H_{12}O_6\). Glucose is an aldohexose, meaning it contains an aldehyde functional group and has six carbon atoms. The structure of glucose is as follows: - Carbon 1: Aldehyde group (\(CHO\)) - Carbon 2, 3, 4, and 5: Hydroxyl group (\(OH\)) and hydrogen atom (\(H\)) on alternating sides - Carbon 6: Primary alcohol group (\(CH_2OH\)) Now, let's draw the glucose molecule: O || C - H (C1) | C - OH (C2) | C - OH (C3) | C - OH (C4) | C - OH (C5) | C - CH2OH (C6) We can now circle the aldehyde functional group in glucose, which is at Carbon 1.

Draw the straight-chain representation of fructose

To draw the straight-chain representation of fructose, we also need to know its molecular formula, which is also \(C_6H_{12}O_6\). Fructose is a ketohexose, meaning it contains a ketone functional group and has six carbon atoms. The structure of fructose is as follows: - Carbon 1: Primary alcohol group (\(CH_2OH\)) - Carbon 2: Ketone group (\(CO\)) - Carbon 3, 4, and 5: Hydroxyl group (\(OH\)) and hydrogen atom (\(H\)) on alternating sides - Carbon 6: Primary alcohol group (\(CH_2OH\)) Now, let's draw the fructose molecule: CH2OH (C1) | C = O (C2) | C - OH (C3) | C - OH (C4) | C - OH (C5) | C - CH2OH (C6) We can now circle the ketone functional group in fructose, which is at Carbon 2.

Key concepts

Aldehyde Sugars

Aldehyde sugars, also known as aldoses, are a type of sugar that contains an aldehyde group. This group is characterized by the presence of a carbon atom double-bonded to an oxygen atom (C=O) and single-bonded to a hydrogen atom. In the case of glucose, a common example of an aldehyde sugar, the aldehyde group is located at the first carbon (C1) in the straight-chain molecular structure. Aldohexoses, like glucose, consist of six carbon atoms. The arrangement includes the aldehyde group at C1, while the rest of the chain consists of hydroxyl groups ( OH) attached to each of the remaining carbon atoms, alternating sides with hydrogen atoms. This specific arrangement allows for important biochemical reactions necessary for cellular energy production. Understanding glucose’s structure helps clarify its role as a primary energy source in living organisms. Its specific configuration facilitates the ease with which it is broken down in glycolysis within cells, releasing the energy needed for various physiological functions.

Ketone Sugars

Ketone sugars, known as ketoses, are sugars that contain a ketone functional group. A ketone group, unlike an aldehyde group, features a carbon atom double-bonded to an oxygen atom situated somewhere other than the terminal carbon in the chain, often within the interior of the molecule. Fructose is a prime example of a ketone sugar. In fructose, the ketone group is found at the second carbon (C2) of a six-carbon backbone, making it a ketohexose. The structural difference between ketone sugars and aldehyde sugars like glucose lies primarily in the placement of the carbonyl group (C=O). Ketoses play significant biological roles, including participation in metabolic pathways like glycolysis and the Calvin cycle. Fructose in particular, aside from being a natural sweetener, is a key actor in hepatic metabolism and can be converted to glucose derivatives inside the liver.

Straight-Chain Molecular Structures

The straight-chain molecular structure is a depiction of chemical compounds where atoms are aligned in a consecutive line without any branches. In carbohydrate chemistry, straight-chain forms provide a simplified way to visualize and study the arrangement of carbon, hydrogen, and oxygen atoms in sugar molecules. For sugars like glucose and fructose, understanding their straight-chain representations is essential for identifying functional groups such as aldehydes in aldoses and ketones in ketoses. Such understandings facilitate the comprehension of how these sugars participate in biological reactions and processes. While many sugars naturally prefer ring-shaped, cyclic structures due to stability, their straight-chain forms reveal interactions that are crucial during reactions. For instance, the straight-chain structure allows the visual identification of the reactive sites necessary for glycosidic bond formation or oxidation-reduction reactions. Consequently, studying these forms aids in the understanding of energy metabolism and synthesis pathways in living organisms.