DNA Replication and Repair

2' deoxyribonucleoside triphosphate  -  The building blocks of DNA replication. A five-membered, oxygen-containing ribose sugar ring that has three phosphate groups attached to its 5' carbon and either an adenine, cytosine, guanine, or thymine base group attached to its 1' carbon.

Base-pair excision  -  One class of DNA repair system. Recognizes and removes single nucleotide mutations that result from unnatural bases.

Daughter strand  -  Refers to the newly synthesized strand of DNA that is copied via the addition of complementary nucleotides from one strand of pre-existing DNA during DNA replication.

DNA Helicase  -  The enzyme responsible for separating the two strands of DNA in a helix so that they can be copied during DNA replication.

DNA Ligase  -  The enzyme responsible for sealing together breaks or nicks in a DNA strand. Responsible for patching together Okazaki fragments on the lagging strand during DNA replication.

DNA Polymerase  -  The enzyme responsible for catalyzing the addition of nucleotide substrates to DNA both during and after DNA replication.

Primase  -  The enzyme responsible for initiating synthesis of RNA primers on the lagging strand during DNA replication.

Holoenzyme  -  A term used to describe a collection of different enzymes that work together in a given process such as DNA replication.

Hydrolysis  -  The process in which water is chemically added to a molecule.

Lagging strand  -  In DNA replication, the strand of pre-existing DNA that is oriented in the 5' to 3' direction with respect to the direction of replication on which synthesis is discontinuous.

Leading strand  -  In DNA replication, the strand of pre-existing DNA that is oriented in the 3' to 5' direction with respect to the direction of replication on which replication is continuous.

Mismatch repair  -  One class of DNA repair system. Recognizes and removes mutations that result from base-pairing that is not complementary.

Okazaki fragment  -  Short stretches of newly synthesized DNA found on the lagging strand during DNA replication.

Origin of replication  -  Site of initiation of DNA replication. Short, usually internal stretch in a DNA helix that opens so that each strand is separate for DNA replication.

Parent strand  -  In DNA replication, refers to the pre-existing single strand of DNA that is copied into a new strand of DNA via complementary base pairing.

Pyrophosphate  -  A two phosphate-containing molecule. In DNA replication, it is released from a 2' deoxyribonucleoside triphosphate during its addition to a growing, newly synthesized DNA strand. Its subsequent hydrolysis provides the energy for the addition reaction.

Replication fork  -  Term used to describe the junction at which nucleotide substrates are being added to a growing DNA chain during DNA replication. Its shape resembles a "Y" where the two branches represent single stranded daughter strands of DNA and the base represents helical DNA.

RNA Primer  -  Short stretches of ribonucleotides (RNA substrates) found on the lagging strand during DNA replication. Helps initiate lagging strand replication and are later removed.

Semi-conservative  -  Refers to the fact that after the replication of one DNA helix each of the two daughter helices that result contain one newly-synthesized and one pre- existing strand of DNA.

Short-patch excision  -  One class of DNA repair system. Recognizes and removes short stretches of DNA that surround mutations resulting from large adducts on a DNA strand that impede DNA replication.

Single-stranded binding protein  -  A protein involved in helping to keep strands of DNA that have been separated by DNA helicase from recoiling in a helix. It works by coating the single strands in such a way as not to cover the bases, allowing them to remain free for base pairing.

Thymine dimer  -  A form of DNA damage that results from radiation. Adjacent thymines on the same strand of DNA form a bond that results in a bulky adduct that can impede DNA replication.

Tautomerization  -  A process in which a molecule undergoes an electron rearrangement that results in a slightly different organization of the same molecule. The two forms of the same molecule are called "tautomers" of each other.