DNA REPLICATION
When DNA is replicated it is copied. DNA replication must occur in bacteria before binary fission. The deoxyribose, phosphate groups, and the nitrogenous bases needed to replicate the DNA are readily available. DNA replication is known as semi-conservative replication. The easiest way to copy something is to trace it that is what semi-conservative replication does. Both of the DNA strands serve as a template to produce a new DNA strand. What we end up with is two copies of the DNA; each copy is half original DNA and half new DNA.
In prokaryotes DNA replication occurs bi-directionally from a single point (the origin of replication or ori site). An enzyme called helicase unwinds and unzips the DNA at the ori site; ATP is needed for this step. DNA replication then proceeds bi-directionally around the circular bacterial chromosome. Single-stranded binding proteins hold the two DNA strands apart and prevent the DNA from zipping back up. DNA polymerase is the enzyme that replicates the DNA and uses both of the DNA strands as templates. DNA polymerase adds complementary nucleotides (1,000 nucleotides per second) in the 5’ —> 3’ direction. Since the two DNA strands run anti-parallel the strands will have to be copied slightly differently. One of the DNA strands is replicated continuously, it is known as the leading strand. The other DNA strand is replicated discontinuously in fragments, it is known as the lagging strand. The lagging strand is replicated in fragment known as Okazaki fragments; they are about 1000 nucleotides long. The Okazaki fragments are knitted together by DNA ligase. E. coli replicates its chromosome in about 40 minutes. DNA polymerase also proof reads as it builds the new DNA strands.
QuIZ TIME!
additional resources
https://openstax.org/books/biology-2e/pages/14-4-dna-replication-in-prokaryotes