Here's why:

* Hydrophobicity: Trp is a highly hydrophobic amino acid, meaning it repels water. It is more likely to be buried within the core of a protein, away from the aqueous environment.

* Polarity: Gln is polar and can form hydrogen bonds with water molecules. This makes it more compatible with the hydrophilic environment of the protein surface.

* Size: Trp is a large amino acid with a bulky side chain, making it less suitable for surface exposure. Gln, on the other hand, has a smaller side chain that can more easily accommodate surface interactions.

Exceptions:

While Gln is generally more surface-exposed than Trp, there are exceptions:

* Specific protein structures: Some proteins may have specific structural requirements that necessitate the presence of Trp on the surface.

* Functional roles: Trp residues can sometimes be involved in protein function and may therefore be found on the surface, such as in protein-protein interactions or binding sites.

In summary:

The general rule of thumb is that Trp is more likely to be buried within a protein's interior, while Gln is more likely to be found on the surface due to its hydrophilic nature and smaller size. However, there are exceptions to this rule, depending on the specific protein and its functional requirements.