DNA Replication

• DNA Replication occurs in S phase.
• DNA needs to replicate before cell division.
• Replication = DNA copies itself exactly.
• Replication occurs in the nucleus in eukaryotes.
• Any mistakes in copying = mutations.
• Cells that do not replicate cannot be cancerous.
• DNA has 4 nitrogenous bases: adenine, cytosine, thymine, and guanine.
• DNA is antiparallel. This means two strands run parallel to each other in opposite directions.
• DNA cannot change its shape, only its direction.
• Semiconservative Replication of DNA is when base pairing allows each strand of DNA to serve as a template for a new strand.
• The new strand of DNA in semiconservative replication is half of the parent template and half of the new strand of DNA.
• DNA copying is replication.
• There are four major enzymes in DNA replication: DNA polymerase, Helicase, Primase, Ligase.
• Proteins prevent hydrogen bonds from bonding again.
• Topoisomerase prevents super coiling.
• DNA polymerase builds hydrogen bonds.
• Helicase breaks hydrogen bonds.
• Primase tells DNA polymerase where to start.
• Ligase glues the DNA fragments together (Okazaki Fragments)
• If the old strand is 3' to 5', the new strand will be 5' to 3'.
• The first step in DNA replication is Helicase breaks the weak hydrogen bonds and unwinds the strands of DNA.
• The second step in DNA replication is primase creates and places an RNA primer which is used to tell DNA polymerase where to start.
• The third step in DNA replication is DNA polymerase II brings complementary nitrogenous bases and they build the DNA strands. DNA polymerase II adds bases and proofreads which results in two new strands.
• The third (and a half) step of DNA replication is DNA polymerase I replaces the RNA primers.
• The fourth step of DNA replication is ligase connects the Okazaki fragments which fills in the gaps and results in two finalized strands.
• DNA polymerase will only move from 5' to 3'.
• RNA primers will not connect to the nucleotide DNA.
• Eukaryotes have multiple origins of replication. They go in multiple directions and work together at the same time.
• A large team of enzymes work together to complete the steps at the same time.
• Prokaryotes have one origin of replication because they are smaller.
• Bacteria is better because they have circular DNA.
• The leading strand of DNA does from 3' to 5' (originally) and 5' to 3' (new strand).
• The lagging strand of DNA goes from 5' to 3' (originally) and 3' to 5' (new strands).
• When the DNA strands are made into two new strands, the lagging strand is shorter than the leading strand.
• Because the lagging strand is shorter, we lose DNA every time our cells replicate.
• When we lose DNA, it is assumed that is why we age and die.
• Telomeres: the tips of eukaryotic chromosomes.
• The enzyme telomerase adds short, repeated DNA sequences to telomeres as the chromosomes are replicated. The enzyme works during embryonic growth but stops after birth.
• Cancer cells turn on telomerase which is why cancer cells are harder to kill.