DNA Replication Unit 4: DNA Chapter 12-2

Review of DNA Structure DNA is a double helix –Two strands of repeating nucleotides The rails of the DNA ladder are made of the sugar-phosphate backbone The steps of the ladder are made up of nitrogenous base pairs (A, T, C, G) –Base pairing rules: A-TT-A C-GG-C

Review of DNA Structure DNA strands are “Anti-parallel”DNA strands are “Anti-parallel”: Two strands run in opposite directions to each other One strand is upside down relative to the other

Chromosomes Wound up DNA (chromatin) held together by proteins(histones)

DNA Replication Process of making a copy of DNA templateDNA strands unwind and each strand serves as a template for making 2 new strands

semiconservative : original newReplication is semiconservative : Each new DNA molecule has 1 original strand and 1 new strand –the original strand is conserved (kept) in the new molecule

Replication is carried out by enzymes

Steps of Replication 1) DNA unwinds and unzips –Helicase –Helicase (an enzyme) unwinds the DNA and breaks the hydrogen bonds between base pairs

2) Replication bubble forms –Primase –Primase (an enzyme) gets the new strand started by creating an RNA primer

3) New Strands are Made –DNA Polymerase –DNA Polymerase (an enzyme) Attaches the complimentary nucleotide to the original DNA strand –Matches nucleotides with their complementary bases

4.) Fragments on the lagging strand are put together –LEADING STRAND: –LEADING STRAND: One strand is built continuously in one direction –LAGGING STRAND: DNA Ligase –LAGGING STRAND: The other strand is built in fragments (pieces) that are ligated (glued) together by DNA Ligase

End Result: 2 identical strands of DNA, each with 1 original strand and one new strand