Learn Turkish: Annenin sterilize etmesi gereken biberonlar mutfakta. - The bottles the mother must sterilize are in the kitchen.

To say "the things someone must do", Turkish uses a possessive structure. The person who has to do the action takes the genitive case (annenin = the mother's) and the action takes the verbal noun form with the matching possessive ending (etmesi = her doing). Literally, this chunk translates to "The mother's her-doing being-necessary bottles."

Why do we need etmesi after sterilize? Can't we just say sterilize gereken?

No, because sterilize is not a standalone verb in Turkish; it is a loanword acting as an adjective. To make it a verb, it must be combined with the helper verb etmek (to do/make). Therefore, the action is sterilize etmek (to sterilize), which becomes sterilize etmesi in this grammatical structure.

Why is it gereken instead of gerek or gerekiyor?

Gerek or gerekiyor are used to form a complete sentence, as in Annenin biberonları sterilize etmesi gerek (The mother needs to sterilize the bottles). However, here we are using a relative clause to describe a noun (biberonlar). To turn "it is necessary" into an adjective meaning "which is necessary," we must use the participle form gereken.

Since the bottles are the things being sterilized, why isn't it biberonları with the accusative case?