Istanbul Airport currently serves as 2 terminals in a single building. There are departing passenger, arriving passenger and public/private transportation floors under the same roof.
The top floor is the International and Domestic Departures floor. Gates 1 and 2 are for prooceding the Domestic Departure Terminal, 3,4,5,6 and 7 doors numbered are suitable for proceeding the International Departure Terminal. In fact, all of the doors open into a single huge hall. Approximate waiting time at the doors is 4-5 minutes during off-peak times and 8-9 minutes during busy times. In cases of extraordinary intensity, it may take up to 15-20 minutes.
If you are flying business class with Turkish Airlines, you can enter the terminal building with priority from Door 5.