How to Differentiate Between Poisonous Snakes and Non Poisonous Snakes. Some snakes harm their prey by injecting venom through their fangs; some of this venom can be harmful to humans, resulting in what we often think of as poisoning...
DNA polymerases cannot initiate DNA synthesis - they can only add on to an existing strand of DNA or RNA. The existing strand is said to prime DNA synthesis. RNA polymerases, however, can begin copying a parent strand with no primer - just as they do in transcription of genes. During DNA replication, RNA primers are produced by RNA polymerases in order to provide a starting point for DNA polymerases to extend from.
Hence, the process proceeds in the 5' â 3' direction, like in DNA replication. However, unlike DNA replication, transcription does not need a primer to start and it uses base pairing to create an RNA copy containing uracil instead of thymine.