What is DNA replication?

• A. The process by which RNA is transcribed from DNA.
• B. The process by which a cell divides its cytoplasm.
• C. The process by which a cell copies its DNA to produce two identical DNA molecules.
• D. The process of translating RNA into protein.

Answer: (C)

DNA replication is the process by which a cell copies its DNA to produce two identical DNA molecules. This must happen before a cell divides so each daughter cell gets a complete genome. The double helix is unwound, and each original strand serves as a template for a new complementary strand, so the two new DNA molecules consist of one old strand and one new strand (semi-conservative replication). Enzymes unzip the DNA, stabilize the exposed strands, and DNA polymerase adds nucleotides in the 3' to 5' direction to build the new strands. The leading strand is synthesized continuously toward the fork, while the lagging strand is made in short Okazaki fragments that are later joined. RNA primers start the synthesis, are later removed and replaced with DNA, and the backbone is sealed. This process is different from transcription (making RNA from DNA) and translation (making protein from RNA), and from cytokinesis (division of the cytoplasm).