Semi conservative model
one new and one old strand in DNA
topoisosmerase
corrects overwinding ahead of replication fork
helicase
untwists SNA and opens single strands of DNA
primase
provides the 3’OH end for DNA polymerase to extend
DNA polymerase
elongation of new DSNA at fork
- only in 5’ to 3’ direction
mainly for repair and primer removal
DNA polymerase 3
moves along template strand, synthesizes leading strand moving towards replication fork
ligase
glues together Okazaki fragments
proofreading and DNA repair
DNA polymerase rereads newly made DNA, replaces wrong nucleotides
Nucelase: cuts out damaged stretches of DNA which are then replaced
ligase seals back up
nuclease
cute out damaged stretched of DNA
mutations in DNA repair
xeroderma pigmentosum
xeroderma pigmentosum
children of the night, recessive defect in nucleotide repair enzymes
- severe reaction to UV rays from sunlight
telomeres
no way to completes the 5’ end, replication produces shorter DNA molecules with uneven ends
telomere in germ cells
telomerase extends telomeres
