Proto-oncogenes are genes that have the ability to become oncogenes (genes that cause cancer). There are many ways to activate proto-oncogenes. Gene duplication can cause an increase in the expression of a particular protein, which can lead to cancer. Exposure to mutagens can cause a mutation on a proto-oncogene, which causes it to become activated. Chromosomal translocations can relocate proto-oncogenes to areas where they are expressed more rapidly. Most proto-oncogenes are involved in cell cycle regulation. Irregular expression of these genes can allow the cell to progress through the cell cycle too rapidly, resulting in unregulated cell division and tumor formation.

Oncogenes can be thought of as cancerous genes, or rather a gene that has the potential to cause cancer. They typically occur when a normal proto-oncogene undergoes a mutation. Proto-oncogenes normally code for growth and development in cells, and tightly regulate these processes. If mutated, these newly cancerous genes can stimulate unregulated growth, a symptom characteristic of cancerous cells.

DNA helicases use ATP to break the hydrogen bonds that separate complementary strands of DNA. During DNA replication, DNA helicases move along the DNA backbone with the replication fork and are responsble for unwinding the DNA at the fork.

RNA polymerase is an enzyme that transcribes RNA from DNA; it is not essential for DNA replication. This enzyme is easy to confuse with primase, whose primary function is to synthesize the RNA primers necessary for replication. DNA polymerase add nucleotides during replication, synthesizing the daughter strand from the parental template. Helicase is responsible for separating double-stranded DNA. Single-strand binding proteins are needed to keep DNA from reannealing after it has been denatured by helicase.

DNA replicates in a semiconservative process. Parental strands are used as templates to synthesize daughter strands, which remain adhered to the parental template creating hybrid molecules of old and new DNA.

The original DNA molecules is "unzipped" by helicase to create the replication fork. DNA polymerase then begins to recruit nucleotides to bind to the exposed template, building the new DNA strand along the parental strand.

Before replication, the DNA helix must be unwound so that the strands can be replicated by DNA polymerase. This unwinding is accomplished by DNA helicase, which interferes with the hydrogen bonds between nucleotide pairs. This intervention creates a small separation between the two strands, known as the replication fork. DNA polymerase binds to the replication fork and recruits nucleotides to build the new DNA strand.

Topoisomerase is responsible for cleaving phosphodiester bonds in order to release torsional tension in the DNA backbone. DNA ligase synthesizes phosphodiester bonds, both on the daughter strand of DNA and in the regions cleaved by topoisomerase. Primase is responsible for synthesizing RNA primers that serve to help recruit and bind DNA polymerase in the replication fork.

In order for DNA polymerase to begin synthesizing base pairs, an RNA primer is needed to assist the binding of DNA polymerase to the DNA template strand. This primer is synthesized by the enzyme primase. Because DNA polymerase always needs an RNA primer before it can bind, primase must synthesize RNA primers on both the leading and lagging strands.

RNA polymerase transcribes molecules of RNA from DNA sequences during transcription, and is not involved in DNA replication.

DNA replication occurs during the S phase of the cell cycle, significantly before prophase of mitosis. During prophase chromosomes are condensed into easily segregated forms, but replication has already occurred. The S phase is the intermediate period of interphase in the cell cycle. The G2 phase follows the S phase, and is subsequently followed by the M phase (mitosis).

The short fragments synthesized on the lagging strand are known as Okazaki fragments. DNA replication does occur in the 5' to 3' direction; this is also the reason that the lagging strand must be synthesized away from the replication fork. DNA is denatured (separated) at the replication fork by an enzyme known as helicase, which breaks the hydrogen bonds between base pairs to allow DNA polymerase and other replication proteins to bind to single-strand DNA.

DNA polymerase I replaces the RNA primer gap with DNA nucleotides. This polymerase is unique in that it has 5'  3' exonuclease activity. This RNA primer is created by primase, it is removed and replaced with DNA by DNA polymerase I, and the remaining nick is sealed by DNA ligase. Bacterial DNA polymerase III, in contrast, is the main polymerase for bacterial elongation. The function of DNA polymerase II is not completely understood. The remaining answer choices are not involved in prokaryotic DNA replication.

DNA repair can, and does, occur during replication. An easy example of this is the proofreading function of several DNA polymerases. This function is carried out due to the enzymes containing an exonuclease function that allows them to excise incorrect base pairs. p53 is an incredibly important protein that is expressed heavily when DNA damage is detected. It is responsible for activating both DNA repair pathways and apoptotic pathways, preventing the cell from passing replication and cell cycle checkpoints. If the DNA damage is irreparable, the cell may undergo apoptosis.