DNA replication

• DNA replication: H bonds break and 2 strands of double helix separate
• semi-conservative model: one new (complimentary) and one parental strand (template)
• DNA strand separation: origins of replication have a specific nucleotide sequence. protein DNA helicase binds to those nucelotides and unwinds the helix and separates parent strands. protein SSBs keeps them separate by blocking h-bonds
• Replication fork: where strands are still joined. leading strand replicates toward the fork and lagging replicates away. this creates a bubble
• the energy source for replication is deoxyribonucleoside triphosphates. these have 3 po4 groups so they are unstable. these are added to dna and hydrolyze 2 phosphates to power condensation reaction and add complimentary nucleotide. endothermic.
• starting synthesis: DNA gyrase eases tension. DNA polymerase III builds complimentary strands (5' to 3') but cannot initiate it since it adds to preexisting new strands
• chain of RNA molecules is constructed by primase, RNA primer. DNA polymerase I later replaces the RNA nucleotides with DNA version
• leading strands are synthesized 5' to 3' direction as DNA polymerase III

  moves with the fork. lagging strands are synthesized by okazaki fragments, but a primer is built before each one is added, and are linked together by enzyme DNA ligase into a single DNA strand.
• exonuclease: DNA pol I and III can backtrack to incorrect nucleotides, extract them, and replace them with the correct one then continue synthesizing.
• dna ligase attaches okazaki fragments together by forming a covalent bond between the sugar and po4 groups of nucleotides to form the lagging strand
• Alfred Hershey and Martha Chase: concluded that DNA is injected into the host cell and replicated, protein stays outside
• adenine (A) and guanine (G): double-ringed structures (purines)

  thymine (T) and cytosine (C): single-ringed structures (pyrimidines)
• FRANKLIN & WILKINS: used xrays to find the 3D shape of DNA to be helical, 2 nm in diameter and complete helical turn every 3.4 nm
• WATSON & CRICK: used prior work to conclude that base pairing is complementary because of width of DNA and capacity of hydrogen bonds of nucleotides. Purines always pair with pyramidines.