How the first biological systems first became capable of replication and translation is one of the major problems in the study of the origins of life. At the present time we are unclear of the details and there are a number of competing theories.
What is clear, however, is that at a molecular level to process of replication is well illustrated by the molecule DNA. As already stated, DNA molecules are formed from two strands of DNA that spiral around each other in a formation called a double helix. The two strands are held together by bonds which is quite specific, so that bonds are always partnered in the same way. This complementarity is crucial for faithful replication of the DNA strands prior to cell division.
During DNA replication, the DNA strands are separated, and each strand serves as a template for the replication of its complementary strand. It is as if the molecule has positive and negative halves, each which produce their opposite during replication, yielding two identical molecules from one original.