The DNA replication origin recognition complex (ORC) is a six-protein machine with a slightly twisted half-ring structure (yellow). ORC is proposed to wrap around and bend approximately 70 base pairs of double stranded DNA (red and blue). When a replication initiator Cdc6 (green) joins ORC, the partial ring is now complete and ready to load another protein onto the DNA. This last protein (not shown) is the enzyme that unwinds the double stranded DNA so each strand can be replicated. Credit: Image courtesy of Brookhaven National Laboratory