It does, actually. There is a technical term that is escaping me at the moment, but it kind of "doubles" the consonant that follows it. So with かっこ, it's actually three units of time to say the term: ka, k, and ko. Put a different way, it sounds like you start to say the ko, then sit on the k for a sec, then continue with こ.
Both かこ and かっこ have audio entries in renshuu, so try looking them both up in the dictionary and listen to them side-by-side.