What type of compound are mucins primarily classified as?

Mucins are primarily classified as glycoproteins due to their structure and function. Glycoproteins are molecules that consist of a protein backbone with attached carbohydrate (sugar) chains. Mucins possess this characteristic, featuring extensive oligosaccharide side chains that contribute to their gel-like properties and their ability to form protective mucous gels.

The glycosylation of mucins plays a crucial role in their biological functions, including lubrication, protection of epithelial surfaces, and facilitating cell signaling. These important roles are largely due to the carbohydrate components, which help to maintain hydration and provide a physical barrier against pathogens and particulate matter.

In contrast, proteins do not have carbohydrate modifications and thus would not account for the specific properties of mucins that are important for their biological functions. Lipids and nucleotides do not share the glycosylated structure or the specific functional characteristics attributed to mucins, further confirming that mucins are best categorized as glycoproteins.