1. DNA Replication DNA Replication is a semiconservative process where the new DNA is copied onto a parental (conserved) strand. It takes place with surprising efficiency and speed copying ~10 billion base pairs in a few hours with little or no errors.

2. Origin of replication Site of initiation of replication – bacteria have a single site while Eukaryotes have multiple sites proteins (enzyme helicase) recognize site and open up a replication bubble – as replication begins a replication forks form as replication proceeds in both directions Nucleotides (ACTG) are added 1 at a time by DNA polymerase (~50/sec) in the 5' to 3' direction (copied 3' to 5') – replication forks eventually fuse completing the newly formed strands

3. Antiparallel elongation leading strand - 3' to 5' – an RNA primer is needed for attachment of DNA pol RNA attached with the enzyme primase – DNA polymerase attaches to the primer and adds nucleotides one at a time in the 5' to 3' direction replication continues until completion or meeting another replication fork – Replicated fragments joined with enzyme ligase

4. lagging strand - 5' to 3' since nucleotides can only be added to the 3' end of the newly forming strand, different mechanisms must be in place for the antiparallel strand – DNA pol attaches at the replication fork and copies back to the growing strand in the 5' to 3' direction small 100 to 200 nucleotide segments called Okazaki fragments – replication continues until DNA pol reaches a primer Primer falls off DNA pol replaces the RNA primer with DNA – Okazaki fragments are joined by DNA ligase as DNA pol detaches

5. Other proteins involved – topoisomerase - relieves supercoiling caused by helicase – single-strand binding protein - stabilizes the DNA strand that has been unwound until it is replicated

6. Telomeres Small sections of DNA at the 3' end of the DNA cannot be replicated as the RNA primer occupies the space. As a result daughter chromosomes are shorter that the parent chromosomes. – telomeres are regions of DNA located at the ends of chromosomes contain 100 - 1000 repeating units (TTAGGG) protect internal gene sequences from erosion get shorter with each replication associated with the aging process – telomerase is an enzyme active in germ cells and restores the length to the chromosomes is inactive in somatic cells – may protect somatic cells from cancer