## Core Concept
Glycoproteins are proteins that have carbohydrate chains (glycans) covalently attached to their polypeptide side-chains. These molecules play critical roles in various biological processes, including cell-cell recognition, immune response, and as receptors or enzymes. The question tests the ability to identify which of the listed options does not belong to the category of glycoproteins.

## Why the Correct Answer is Right
The correct answer, **D. Histone**, is right because histones are a family of basic proteins whose main function is to form a core around which DNA winds, and they do not have carbohydrate chains attached to them. Histones are crucial for DNA packaging into nucleosomes, which is a fundamental process in eukaryotic cells.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is a glycoprotein because many proteins with functions such as enzyme activity, hormone activity, or transport across cell membranes are indeed glycoproteins.
- **Option B:** Similarly, this option represents a glycoprotein, given the diverse roles glycoproteins play in biological systems.
- **Option C:** This is also a glycoprotein, reflecting the wide prevalence of glycoproteins in biological systems.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while many proteins are modified with carbohydrate chains (glycoproteins), not all proteins have such modifications. For example, histones, which are crucial for DNA packaging, do not contain carbohydrate chains and thus are not glycoproteins. This distinction can be critical in understanding protein function and classification.

**Correct Answer: D. Histone**