1. Chromosome Structure
In prokaryotes, DNA molecules are contained in cytoplasm and consists mainly of a ring of DNA and associated proteins.
Eukaryotic DNA :individual chromosomes.
DNA : coiled around a group of beadlike proteins called histones.
The phosphate groups in DNA (negative charge), attracts the DNA to the positively charged histone proteins (nucleosome).
The nucleosomes form chromatin fibers, which supercoil to make up a chromosome.

2. Semiconservative Replication
Parental strands of DNA separate, serve as templates, and produce DNA molecules that have one strand of parental DNA and one strand of new DNA.

3. Semiconservative Replication
Occurs in three main stages:
Unwinding
DNA helicase: unwinding and unzipping the double helix.
RNA primase: adds a short segment of RNA, RNA primer, on each DNA strand.
Base pairing
DNA polymerase continues adding appropriate nucleotides to the chain by adding to the 3′ end of the new DNA strand.
Two strands made in slightly different manner.

4. Base Pairing
One strand (leading strand) is elongated as the DNA unwinds; built continuously by addition of nucleotides to the 3’ end.
The other strand,( lagging strand), elongates away from the replication fork.
It is synthesized discontinuously into small segments, called Okazaki fragments, by the DNA polymerase in the 3’ to 5’ direction.
Because one strand is synthesized continuously and the other discontinuously, DNA replication is said to be semicontinuous

5. Joining
DNA polymerase removes the RNA primer and fills in the place with DNA nucleotides.
DNA ligase links the two sections.
Eukaryotic DNA: unwinds in multiple areas as DNA is replicated.
In prokaryotes: the circular DNA strand is opened at one origin of replication.

6. Prokaryotic Replication
Bacteria have a single loop of DNA that must replicate before the cell divides.
Replication only proceeds in one direction, from 5' to 3'.
Bacterial cells are able to replicate their DNA at a rate of about 106 base pairs per minute.
Bacterial cells can complete DNA replication in 40 minutes; eukaryotes take hours.

7. Eukaryotic Replication
Starts at many points of origin and spreads with many replication bubbles—places where the DNA strands are separating and replication is occurring.
Replication forks are the V-shape ends of the replication bubbles; the sites of DNA replication.
Eukaryotes replicate their DNA at a slower rate – 500 to 5,000 base pairs per minute. 7

8. Replication Errors
A genetic mutation is a permanent change in the sequence of bases.
A mismatched nucleotide may occur once per 100,000 base pairs, causing a pause in replication.
Proofreading is the removal of a mismatched nucleotide; DNA repair enzymes perform this proofreading function and reduce the error rate to one per billion base pairs. 8