Question

which substitution would you expect to have the least impact on the shape of a protein?
substituting a hydrophobic amino acid with a hydrophilic amino acid
increasing the length of the amino acid chain by one amino acid
reducing the length of the amino acid chain by one amino acid
substituting a hydrophilic amino acid with a hydrophobic amino acid
substituting a hydrophobic amino acid with a hydrophobic amino acid

Explanation:

Protein shape depends on amino acid properties (e.g., hydrophobicity) and sequence length. Substituting a hydrophobic amino acid with another hydrophobic one preserves the key property affecting folding (hydrophobic interactions), so it has the least impact. Changing length (adding/removing amino acids) or swapping hydrophobic/hydrophilic types disrupts folding more significantly.

Answer:

substituting a hydrophobic amino acid with a hydrophobic amino acid