DNA Replication: the mechanism by which DNA is copied. (Brooker, 219)

The original … two "strands" of DNA separate and serve as “template strands” for the synthesis of new strands of DNA. The end result is that two (new) "double helices" are made that have the same base sequence as the original DNA molecule. (Brooker, 219-220) DNA replication is an important part of the "cell cycle." (Indge, 86-87) Only occurs during the 'S-phase' of the cell cycle. (Lewis, 174) Three important issues are speed, fidelity, and completeness. DNA replication must proceed quickly, with great accuracy, and gaps should not be left in the newly made strands. (Brooker, 225) The rate of replication is fast: 50 to 500 "nucleotides" per second, with faster replication at younger ages. (Norman 7/7/09)

Binary Fission: DNA replication process in "bacteria." Referred to as mitosis in "eukaryotes." (Norman, 81) The process of cell division in bacteria and “archaea” in which the cells divide into two cells. (Brooker, G-4)

DNA Replication Enzymes: "enzymes" used in the replication process. (Norman, 7/7/09)

DNA Ligase: seals the sugar phosphate pieces building the new strand. (Lewis, 175) A family of enzymes that catalyze the formation of 'phosphodiester bonds' to repair broken strands of DNA. (NCIt) Covalently attaches adjacent "okazaki fragments." (Brooker, 224) An enzyme capable of linking DNA into a ring. (In addition to DNA replication) used (by researchers) to join the ends of the "phi X 174" (bacteriophage) DNA that had been copied. The duplicated DNA was now capable of infecting a bacterium. (Venter, 64) Also referred to as 'ligase."

DNA Polymerase: enzyme responsible for linking nucleotides together to form DNA strands. (Brooker, 222) Catalyzes the addition of "deoxyribonucleotide" residues to the end of a DNA. (NCIt) Makes DNA from the "RNA"  "primers." Then ‘hops’ back to the opening of the fork and makes a second RNA primer for the "lagging strand." Continues to elongate the "leading strand." In the lagging strand, synthesizes DNA from the ‘second primer,’ and also removes the first primer and replaces it with DNA. (Brooker, 225) Matches nucleotide bases of the "parent strand" with free nucleotides (called ‘deoxynucleoside triphosphates’). (Norman, 7/7/09) Can only link nucleotides (by moving) in the 5’ to 3’ direction. (Brooker, 224) Discovered by Arthur Kronberg. Links the DNA components and makes the chemical bonds of the DNA backbone. (Watson, 60) In humans, over a dozen different DNA polymerases have been identified. (Brooker, 225) Have played a critical role in "DNA sequencing." (Venter, 67)

Helicase: binds to the start of a DNA segment. Unwinds and opens up the DNA helix during DNA replication. (Lewis, 174) Breaks the "hydrogen bonds" between the nucleotides as it proceeds. (Norman, 7/7/09) Travels along one DNA strand in the 5’ to 3’ direction and separates the DNA strands. Separates double-stranded DNA into single strands. (Brooker, 223-224)

Primase: makes RNA primers to begin the replication process. (Brooker, 225) Synthesizes short RNA primers. (Brooker, 224)

Telomerase: RNA containing enzyme responsible for replicateing telomeres. (Lawrence) Attaches many copies of repeated DNA sequences to the ends of "chromosomes." (Brooker, 226) Catalyzes the synthesis of DNA from RNA. (Norman, 7/2/09)

Topoisomerase: enzymes that can untwist tangled or supercoiled DNA by making transient single-strand breaks around which the rest of the DNA molecule can swivel. (Lawrence) Travels slightly ahead of the replication fork and alleviates coiling... (Brooker, 223) Alleviates coiling due to helicase actions. (Norman, 7/7/09)

Okazaki Fragments: short segments of DNA “synthesized” in the lagging strand during DNA replication. (Brooker, G-26) DNA ligase forms a bond between Okazaki fragments. (Brooker, 225) Discovered by Reiji Okazaki at Nagoya University in Japan. Proposed that one strand of DNA is synthesized continuously in the 5’ to 3’ direction. Synthesis on the other strand also occurs in the 5’ to 3’ direction but in small discontinuous stretches. These stretches are later joined together into a continuous strand. (Micklos, 40)

Origin of Replication: part of a chromosome. The start of a DNA segment where helicase begins its work. (Lewis, 174) The site within a chromosome that serves as a starting point for DNA replication. At the origin, the two DNA strands unwind, and DNA replication proceeds outwards from the origin in opposite directions. (Humans) have chromosomes that are linear. They require multiple origins of replication so that the DNA can be replicated in a reasonable length of time. The newly made strands from each origin eventually make contact with each other to complete the replication process. The synthesis of a strand always begins with a “primer” and the new DNA is made in the 5-prime to 3-prime direction. (Brooker, 221)

Primer: a short segment of RNA, typically 10 to 12 nucleotides in length. These short RNA strands start, or 'prime' the process of “DNA replication.” (Brooker, 224) Added by ‘primase’ to the DNA “template strand.” (Lewis, 175) Also referred to as 'RNA Primer' and 'DNA Primer.’

Proof Reading: the ability of DNA Polymerase to recognize mismatched bases. (Lawrence) The process by which DNA polymerase can identify a mismatched nucleotide and remove it from the “daughter strand.” The "active site" is unlikely to “catalyze” bond formation between adjacent nucleotides if a mismatched base pair is formed. (Brooker, 224)

Replication Fork: the area where two DNA strands have separated and new strands are being synthesized. DNA strands separate at origin, creating a ‘replication bubble’ and 2 replication forks. The synthesis of the leading strand begins in the direction of the replication fork. (Brooker, G-31) Site of unwinding of double-stranded DNA and synthesis of new DNA. It is seen in electron micrographs of replicating DNA, as a Y-shaped structure. (Lawrence)

Single-Strand Binding Protein: stabilizes unwound DNA. (Norman, 7/7/09) Coats the DNA strands to prevent them from re-forming a double helix. (Brooker, 223)