Mad cow disease is an infectious disease where one misfolded protein causes all other copies of the protein to begin misfolding. this is an example of a disease impacting structure.
primary
secondary
tertiary
quaternary

Tertiary structure

Explanation:

The tertiary structure of a protein includes the overall three-dimensional arrangement of all the atoms of a protein. The amino acid residue located far apart from each other in a protein and have different secondary structures interact and determine the overall folding pattern of the proteins.

Therefore, when any condition such as mad-cow disease causes misfolding of protein, it affects the tertiary structure of the proteins since the overall folding pattern of the protein reflects its tertiary structure.  

tissue

explanation:

it is actually formed by geoup of cells which is tissue