First appeared 1.5 billion years ago. The DNA has free ends and is not bound to any membranes.
Replication starts at several points.
Nuclear structure of the membrane. It has been shown that proteins derived from these ribosomes on the 'nuclear membrane' can be channeled through the inner membrane space of the r.e.r. , then smooth e.r. and end up in the Golgi apparatus. The outer structure of the nucleus actually seems to come from a strong structural protein layer called the nuclear lamina. Then the r.e.r. simply folds around this already existing structural protein surface. The transport properties of the nuclear membrane are poorly understood.