"transactions are replicated before check point occurs in transactional replication "
I don't really understand that statememt... where did you see it?
The checkpoint process has nothing to do with replication. It writes changed pages from memory to disc.
The only tie in with replication is with truncation of the transaction log. In simple recovery, this normally happens after a checkpoint, but if there are replicated transactions in the log, truncation of the log has to wait until they have been processed as well.