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Enzymes & Structures: Topioisomerase SSBPs (single stranded binding proteins) Primase DNA LigaseLeading Strand Nucleoside Triphosphates Lagging Strand DNA Polymerase IIIExonucleases DNA Helicase DNA Polymerase I

Enzymes used in DNA replication

DNA Replication :existing DNA strands serve as templates for new complementary strands

Semiconservative = new DNA has 1 old 1 new strand

3 stages: initiation, elongation, & termination. Enzymes do all the work!

INITIATION1. Helicase untwists and separates template DNA strands from the origin of replication by breaking H-bonds and moves along the direction of leading strand

2. SSBPs (single-stranded binding proteins) keep the unpaired template strands apart during replication

Q: How does the DNA keep from getting super twisted as helicase opens up more DNA??

3. Topioisomerasereleases any tension brought about by the unwinding of the DNA strands (humans have 4)

4. Primase attaches RNA primer as soon as there is a single strand = landing strip for DNA pol III

ELONGATION5. DNA polymerase III catalyzes elongation of new DNA and attaches free nucleotides to the growing new strand.

6. Leading strand is replicated continuously towards replication fork while lagging strand is replicated in Okazaki fragments. The growing direction of the new DNA strand is always 5 to 3 leading strand always starts with 3 prime.

7. DNA polymerase I checks over the new replicated DNA strand and removes the RNA primer.

TERMINATION8. DNA ligase adds sugar phosphate backbone between the Okazaki fragments (fills in gaps)