A replication fork
Double-stranded DNA (dsDNA) is extremely stable, but single-stranded DNA (ssDNA) is extremely unstable. Single-Stranded Binding Proteins (SSBPs) protect ssDNA while it is being replicated. Note again that the DNA strands are anti-parallel, and that therefore replication on either strands starts from 5’3’ RNA primers and also runs in antiparallel directions.
Figure © 2000 by Griffiths et al. ; All text material © 2007 by Steven M. Carr