Honors Biology – DNA Replication & Repair

DNA helicase

unwinds the double helix by breaking hydrogen bonds between bases

DNA polymerase

adds new complementary bases and proofreads for errors during replication

DNA ligase

seals gaps between Okazaki fragments by bonding sugar-phosphate backbones

primase

lays down RNA primers so polymerase can start building

replication origin

starting point where replication begins and polymerase binds

replication fork

y-shaped region where the DNA is actively being unzipped and copied

replication bubble

entire opened region of DNA with two forks moving in opposite directions

leading strand

built continuously from origin to fork in the 5’ to 3’ direction

lagging strand

built in fragments from fork to origin in 5’ to 3’ direction

Okazaki fragments

short segments of DNA made on the lagging strand

semi-conservative replication

each DNA copy has one original strand and one new strand

mutation

a change in the DNA sequence; can be harmful, harmless, or lethal

DNA repair

mechanism that fixes errors during or after replication

exonuclease

enzyme that removes incorrect nucleotides from the strand

excision repair

system using exonuclease, polymerase, and ligase to fix mutations

S phase

stage of interphase when DNA replication occurs