Tendon — there’s something wrong we turned up (5)
I believe the answer is:
sinew
'tendon' is the definition.
(I know that tendon can be written as sinew)
'there's something wrong we turned up' is the wordplay.
'there's' says to put letters next to each other.
'something wrong' becomes 'sin' (something morally wrong).
'turned up' says the letters should be written in reverse.
'we' reversed gives 'ew'.
'sin' next to 'ew' is 'SINEW'.
(Other definitions for sinew that I've seen before include "power source" , "Tendon, for example" , "Muscular strength" , "source of physical strength" , "It indicates strength" .)