Question

Many plasma glycoproteins are protected from uptake and degradation by the hepatocytes in liver due to the presence of a terminal saccharide moiety known as

• A. N-Acetylneuraminic acid
• B. N-Acetylgalactosamine
• C. D-Galactose
• D. D-Mannose

Hint:

The presence of sialic acid (N-Acetylneuraminic acid) on glycoproteins helps in evading recognition by the liver and prolongs the glycoprotein's half-life in circulation.

Answer 1

The Correct Option is A

Step 1: Understanding the role of terminal saccharide moieties.
Terminal saccharides like N-Acetylneuraminic acid (also known as sialic acid) are often found on glycoproteins, and these modifications play a crucial role in preventing their recognition and degradation by the liver. This modification protects plasma glycoproteins from premature clearance.

Step 2: Analyzing the options.
(A)N-Acetylneuraminic acid: Correct — N-Acetylneuraminic acid (sialic acid) is a terminal sugar that protects glycoproteins from uptake and degradation by hepatocytes.
(B)N-Acetylgalactosamine: This sugar is found in glycoproteins but does not have the same protective role as N-Acetylneuraminic acid.
(C)D-Galactose: While D-galactose is important in glycoproteins, it does not have the specific protective function mentioned in the question.
(D)D-Mannose: This sugar is involved in glycoprotein recognition but does not directly protect glycoproteins from degradation in the liver.

Step 3: Conclusion.
The correct answer is (A)N-Acetylneuraminic acid, as it is the saccharide responsible for protecting glycoproteins from degradation.