Question

Glucose and ........... are epimers with regards to carbon 4 ($C_4$ - epimers).

• A. Mannose
• B. Ribose
• C. Maltose
• D. Galactose

Hint:

Remember these key epimer pairs:
- Glucose and Galactose are $C_4$-epimers.
- Glucose and Mannose are $C_2$-epimers.
This is a common question in biochemical exams.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Epimers are a subclass of diastereomers that differ in the stereochemical configuration around only one chiral carbon atom.
Key Principle:
Alhexose sugars share the same molecular formula ($C_6H_{12}O_6$) but differ in the spatial orientation of their hydroxyl (-OH) groups.

Step 2: Detailed Explation:
D-Glucose is an aldohexose with chiral centers at carbons $C_2$, $C_3$, $C_4$, and $C_5$.
In the standard Fischer projection of D-Glucose, the hydroxyl groups are oriented to the right on $C_2$, the left on $C_3$, the right on $C_4$, and the right on $C_5$.
D-Galactose is also an aldohexose with the same carbon backbone.
When comparing the structures of D-Glucose and D-Galactose, they are identical at $C_2$, $C_3$, and $C_5$.
The only structural difference lies at $C_4$, where the hydroxyl group is oriented to the right in glucose but to the left in galactose.
Because they differ in configuration only at $C_4$, Glucose and Galactose are $C_4$-epimers.
For comparison, D-Mannose differs from glucose only at the $C_2$ position, making Mannose and Glucose $C_2$-epimers.
Ribose is a five-carbon aldopentose, and Maltose is a disaccharide.

Step 3: Fil Answer
Thus, Glucose and Galactose are epimers with respect to carbon-4.