Question

Indicate the chiral carbon atoms found in the monosaccharides D-ribose and D-mannose.

Short answer

In D-ribose, the chiral carbon atoms are C2 and C3, while in D-mannose, the chiral carbon atom is C2.

Step-by-step solution

Write the molecular formula of D-ribose and D-mannose

First, let's write the molecular formula of D-ribose and D-mannose: D-ribose: C5H10O5 D-mannose: C6H12O6

Draw the Fischer projection of D-ribose and D-mannose

Now, let's draw the Fischer projection of D-ribose and D-mannose, which shows the arrangement of atoms in these molecules in a 2D representation: D-ribose: ``` HO HO HO HO H | | | | | H-C- H-C- H-C- H-C- C=O | | | | | OH OH H OH H ``` D-mannose: ``` HO HO HO HO H | | | | | H-C- H-C- H-C- H-C- C=O | | | | | OH H H OH H ```

Identify the chiral carbon atoms

Now, let's identify the chiral carbon atoms in each molecule. We are looking for carbon atoms with four different substituents attached to them: In D-ribose: - C2 (the second carbon from the top) has the following substituents: H, OH, C1 (attached to H and OH), and C3 (also attached to H and OH). - C3 has the following substituents: H, OH, C2 (listed above), and C4 (attached to H and OH). Both C2 and C3 are chiral because they have four different substituents. In D-mannose: - C2 has the following substituents: H, OH, C1 (attached to H and OH), and C3 (attached to H and OH). - C3 (the third carbon from the top) has the following substituents: H, H, C2 (listed above), and C4 (attached to H and OH). Only C2 is chiral in D-mannose, as C3 does not have four different substituents.

Indicate the chiral carbons

Finally, let's indicate the chiral carbons in D-ribose and D-mannose: In D-ribose, the chiral carbons are C2 and C3. In D-mannose, the chiral carbon is C2.

Key concepts

Fischer projection

The Fischer projection is a critical tool in understanding the structure of monosaccharides. It offers a two-dimensional way of representing the three-dimensional structure of molecules. Specifically, it is used for showing the spatial arrangement of atoms around chiral centers in carbohydrates.
When drawing the Fischer projection of a sugar like D-ribose or D-mannose, the carbon chain is drawn vertically. The aldehyde or ketone group, which is often at one end of the molecule, is placed at the top. Horizontal lines represent bonds projecting out of the plane towards the viewer, while vertical lines indicate bonds going into the plane.
This method of representation helps to easily identify chiral centers, as the different groups attached to the chiral carbon can be clearly seen.

Chiral carbon atoms

Chiral carbon atoms are carbons that have four different groups attached to them, giving rise to stereoisomerism. This characteristic is vital in determining the function and properties of the molecules they constitute. The presence of chiral carbons in monosaccharides like D-ribose and D-mannose affects their three-dimensional shape and their interaction with biological systems.
In the Fischer projections of D-ribose and D-mannose, identifying chiral carbons involves looking for carbons bonded to four different groups. For D-ribose, both C2 and C3 carbons are chiral, due to the distinct arrangement of hydrogen, hydroxyl, and carbon chain groups. In D-mannose, only C2 is considered chiral because C3 has two hydrogen atoms, making it achiral.
The chirality plays a crucial role in defining each sugar's biochemical activity and its interactions with enzymes and receptors.

D-ribose

D-ribose is an aldopentose, meaning it is a five-carbon sugar with an aldehyde group. Its formula is C5H10O5, and its structure can be depicted using a Fischer projection to highlight the chiral nature of its carbons.
In its Fischer projection, D-ribose has three chiral centers, namely C2, C3, and C4, although only C2 and C3 are commonly noted. The presence of these chiral centers influences its form and function, particularly in the formation of ribonucleic acid (RNA) and energy-carrying molecules like ATP.
Understanding the chirality and structure of D-ribose is essential for appreciating its role in essential biological pathways and its importance in molecular biology.

D-mannose

D-mannose is an aldohexose, characterized by its six-carbon backbone and an aldehyde group. Its molecular formula is C6H12O6, and it plays significant roles in human health, particularly in maintaining urinary tract health.
The Fischer projection of D-mannose reveals its structural arrangement - where C2 acts as a chiral carbon. The orientation of the hydroxyl and hydrogen groups around C2 is what uniquely identifies D-mannose compared to other sugars.
Due to its structural characteristics, especially the chiral nature of its components, D-mannose can be metabolized in specific ways by different organisms, making it an interesting molecule to study in fields like glycoprotein synthesis and cellular recognition.