A discrete, locally folded unit of protein tertiary structure usually having a specific function best describes . A discrete, locally folded unit of protein tertiary structure usually having a specific function best describes . a domain a motif a complex quaternary structure

a domain

Explanation:

The domains are the basic units of the proteins, they are polypeptide segments (about 30 -200 amino acids) that have a defined tertiary structure and play specific biological functions including, for example, enzymatic and structural activities. Protein domains are evolutionary conserved, it means that these polypeptide segments can be found in phylogenetically related species and share sequence homology. Examples of protein domains include the zinc finger and the helix-turn-helix domains which are involved in protein-DNA interactions of transcription factors.

geologic time scale (for gradpoint) =)