Hey Ty. Thanks for your question.
DNA replication is a complex process that involves many steps, proteins, and chemical reactions. The bottom line, though, is to remember a few key details:
- In order for DNA to replicate, it must first "unzip". This means that the two strands must come apart from each other, sort of like cutting a ladder in half by sawing each rung in half.
- Once DNA is unzipped, replication can occur. A protein called DNA polymerase reads the "old" strand (the one that already existed) and builds the new strand complementary to the old strand.
- A very important rule: Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).
- The old strand is read in the 3' --> 5' direction and the new strand is built (synthesized) in the 5' --> 3' direction.
Those are the main points to remember when thinking about DNA replication. To explicitly answer your first question, the sequence of the new DNA strand is determined by the old DNA strand, and pairing complementary bases with each other (See #3 above).
For your second question, the answer is that both strands are replicated in much the same way, except that one strand is synthesized continuously because it is being synthesized in the SAME direction as the old DNA is being unzipped, and the other new strand is synthesized in segments because it is heading in the OPPOSITE direction that the DNA is being unzipped.
Hope this helps. Please reach out if I can be of more assistance!