Chapter 25: Problem 9
How many chiral centers are present in D-glucose? In D-ribose?
Short Answer
Expert verified
Answer: D-glucose has 4 chiral centers, while D-ribose has 3 chiral centers.
Step by step solution
01
Locate the structure of D-glucose and D-ribose
Look up the structures of D-glucose and D-ribose to identify the carbon atoms with four different groups attached to it.
D-glucose: C1H11O6 with structure HOCH2-(CHOH)₄-CHO
D-ribose: C5H10O5 with structure HOCH2-(CHOH)₃-CHO
02
Identify chiral centers in D-glucose
In D-glucose, each of the carbon atoms (except the first carbon, C1, and the sixth carbon, C6) has four different groups attached to it.
The chiral centers are at:
C2: with groups -OH, -H, -CHOHCH₂OH, and -CHOHCH20H
C3: with groups -OH, -H, -CHOHCH₂OH, and -CHOHCH2OH
C4: with groups -OH, -H, -CHOHCH2OH, and -CH2OH
C5: with groups -OH, -H, -CH2OH, and -CHOHCH₂OH
Thus, there are 4 chiral centers in D-glucose.
03
Identify chiral centers in D-ribose
In D-ribose, each of the carbon atoms (except the first carbon, C1) has four different groups attached to it.
The chiral centers are at:
C2: with groups -OH, -H, -CHOH₂CHOH, and -CHOHCHO
C3: with groups -OH, -H, -CHOHCHO, and -CHOH₂CHOH
C4: with groups -OH, -H, -CHOHCHO, and -CHOHCHO
Thus, there are 3 chiral centers in D-ribose.
04
Conclusion
In D-glucose, there are 4 chiral centers, and in D-ribose, there are 3 chiral centers.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
D-glucose Structure
Let's delve into the structure of D-glucose, which is a monosaccharide, commonly known as a simple sugar. It consists of a chain of six carbon atoms, where the first (C1) is part of an aldehyde group (CHO), and the remaining five are part of a hydrocarbon chain (C2-C6). To precisely understand its three-dimensional form, it's important to recognize that D-glucose is a polyhydroxy aldehyde.
Each carbon atom in D-glucose, except for the first and last, is connected to four distinct groups – resulting in a total of four chiral centers. These are located at carbon atoms C2, C3, C4, and C5. The configuration of these chiral centers is crucial as it determines the glucose's D-configuration. Specifically, D-glucose has the -OH group on the right at the chiral carbon furthest from the aldehyde group when drawn in a Fischer projection.
Each carbon atom in D-glucose, except for the first and last, is connected to four distinct groups – resulting in a total of four chiral centers. These are located at carbon atoms C2, C3, C4, and C5. The configuration of these chiral centers is crucial as it determines the glucose's D-configuration. Specifically, D-glucose has the -OH group on the right at the chiral carbon furthest from the aldehyde group when drawn in a Fischer projection.
D-ribose Structure
Now, turning our attention to D-ribose, which is a pentose sugar with five carbon atoms, forming the backbone of the ribonucleic acid (RNA) structure. Unlike D-glucose, D-ribose has an aldehyde group at C1 and four other carbon atoms (C2-C5). Among these, C2, C3, and C4 are chiral centers, making for three chiral centers in total.
This sugar also follows the D-configuration, which means when drawn in the Fischer projection with the aldehyde at the top, the hydroxyl group (-OH) at the chiral carbon furthest from the aldehyde is to the right. D-ribose's relevance extends to its role in RNA formation, where it serves as the sugar backbone, connecting with phosphate groups and nitrogenous bases.
This sugar also follows the D-configuration, which means when drawn in the Fischer projection with the aldehyde at the top, the hydroxyl group (-OH) at the chiral carbon furthest from the aldehyde is to the right. D-ribose's relevance extends to its role in RNA formation, where it serves as the sugar backbone, connecting with phosphate groups and nitrogenous bases.
Stereochemistry
Stereochemistry is a sub-discipline of chemistry that involves the study of the three-dimensional arrangement of atoms within molecules. Understanding stereochemistry is pivotal for comprehending how molecules interact with one another and how their structure affects their function, particularly in biological systems.
The concept of chirality, part of stereochemistry, is featured in molecules that are non-superimposable on their mirror images, similar to how your left and right hands are mirror images but not identical. This characteristic is crucial in biochemistry, as it can influence the way molecules such as drugs interact with biological targets like enzymes and receptors.
The concept of chirality, part of stereochemistry, is featured in molecules that are non-superimposable on their mirror images, similar to how your left and right hands are mirror images but not identical. This characteristic is crucial in biochemistry, as it can influence the way molecules such as drugs interact with biological targets like enzymes and receptors.
Carbohydrates Chirality
Carbohydrates often contain multiple chiral centers, which are the particular carbon atoms bonded to four different atoms or groups. This trait renders carbohydrates chiral, potentially existing in multiple forms, known as stereoisomers. These stereoisomers have distinctly different biological activities and properties, despite having the same molecular formula.
For instance, while D-glucose is the main energy source for most living cells, its stereoisomer, L-glucose, is not metabolically useful. This emphasizes the significance of chirality in biological systems, and why understanding carbohydrates' stereochemistry is fundamental in fields such as pharmacology and biochemistry.
For instance, while D-glucose is the main energy source for most living cells, its stereoisomer, L-glucose, is not metabolically useful. This emphasizes the significance of chirality in biological systems, and why understanding carbohydrates' stereochemistry is fundamental in fields such as pharmacology and biochemistry.