DNA Replication

Beginning of DNA Replication Begins at Origins of Replication Two strands open forming Replication Forks (Y-shaped region) New strands grow at the forks

Enzymes in DNA replication HELICASE unwinds parental double helix DNA POLYMERASE binds nucleotides to form new strands LIGASE joins Okazaki fragments and seals other breaks in sugar-phosphate backbone

Replication Step 1: HELICASE unzips DNA down the middle by breaking Hydrogen bonds.

Step 2: DNA POLYMERASE moves along the 2 strands and attaches base pair nucleotides to each original parent strand.

Step 3: Replication moves in only in the 5’ to 3’ direction. So, small DNA segments called OKAZAKI FRAGMENTS are made on the other strand.

Step 4: DNA LIGASE seals up all of the gaps in the DNA molecule, like the Okazaki fragments.

Result: 2 identical DNA molecules are formed from the original. hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/ / /micro04.swf::DNA%20Replication%20Fork hill.com/sites/ /student_view0/chapter3/animation__dna_replication__qu iz_1_.html

Semi-conservative Model The two strands of the original molecule separate, and each acts as a template for a new complementary (matching) strand New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA