The natural breaking down of proteins? (3)
I believe the answer is:
rot
'the natural breaking down' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'of proteins?' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ROT' is hidden within 'proteins'.
Can you help me to learn more?
(Other definitions for rot that I've seen before include "crumble" , "Cobblers" , "Rhubarb" , "Deterioration" , "Codswallop" .)