Question 60403

What are tertiary structure, motif and domain?
I really don’t understand these three terms. If you could explain with illustration it would be of great help.

Some of my doubts:

‘The overall 3D structure of the polypeptide chain is referred to as the protein’s tertiary structure.’

-All molecules have a 3D structure, even a linear polypeptide chain has a three dimensional structure so do alpha helix and beta pleated sheet,but here I don’t understand what is meant by ‘overall 3D structure’, is it the 3D structure of an Alpha helix (when aprotein is formed of a single alpha helix)?

A linear polypeptide (primary structure) through specific intra-chain H-bonding form alpha helix and beta pleated sheet(secondary structure), but how does the secondary structure contribute to tertiary structure?

How is a motif different from tertiary structure?

What is a domain actually?