Which is the largest biological molecule?

Proteins are considered the largest biological molecules due to their complex structures and the significant variability in their size. Proteins are made up of long chains of amino acids, sometimes exceeding thousands of amino acids in length, creating intricate three-dimensional shapes that are crucial for their function.

The size of proteins can vary considerably, with some being relatively small, but others, such as titin, can be among the largest known proteins, consisting of over 34,000 amino acids and playing essential roles in muscle contraction and elasticity.

When comparing proteins to other biological macromolecules, it's important to note that while nucleic acids (like DNA and RNA) also have large structures, their primary function is usually related to the storage and transmission of genetic information rather than direct cellular functions. Carbohydrates and lipids, while they can also be large and complex, generally do not reach the molecular scale and diversity seen in proteins.

Therefore, due to their vast diversity, complexity, and functional importance, proteins stand out as the largest biological molecules among the options provided.