REPLICATION OF DNA 1. Origins of replication-specific nucleotide sequences along the DNA molecules to which certain proteins (DNA B) can attach and begin replication; hundreds per eukaryotic chromosome. 2. Replication forks- the Y-shaped places where DNA is being unzipped by helicases; replication is bidirectional; two replication forks form at each origin and move in both directions. 3. Helicases-enzymes that break the H bonds linking the complementary bases and unzip the two sides of the helix. 4. Topoisomerases (swivelases) breaks one side of the helix ahead of where helicase is unzipping it and allows it to swivel and untwist to relieve the strain. 5. Single strand binding proteins (SSB)-attach to the backside of each of the unzipped strands and hold them apart and keep them from kinking.

REPLICATION OF DNA 6. RNA primase-enzyme which lays down a short piece of RNA primer to provide a 3’ end for DNA polymerase III to start from. Neither of the DNA polymerases can start from “scratch” they can only add nucleotides to an existing 3’ end. 7. DNA polymerase III -actually a complex of several enzymes; it is fast but can only attach new nucleotides to the 3’ end of an existing strand; also can not fill in the last 3-5 nucleotides in a gap 8. DNA polymerase I -much slower removes the RNA primer nucleotides and replaces them with DNA nucleotides attaching them to the 3’ of the last Okazaki fragment, it is also used in repair 9. Leading Strand-side of the new DNA which has a 3’ end to which DNA polymerase III can attach and rapidly add new nucleotides after only one short RNA primer is added

REPLICATION OF DNA 10. Lagging Strand-side with a 5’ end, thus new RNA primers must be added every nucleotides, so the DNA p III can attach DNA nucleotides to the 3’ end working back toward the origin of replication 11. Okazaki fragments-sections of DNA nucleotides long which are formed on the lagging strand between primers, after DNA p III runs into the next primer it pulls out and DNA p I comes in, removes the RNA primer and replaces it with DNA but it cannot make the last bond between the sugar and phosphate 12. DNA Ligase-enzyme that connects the new DNA segment to the growing DNA strand, by joining the last sugar and phosphate together

P.A. Levene-a prominent molecular biologist in the 40’s. He determined the structure of a nucleotide but then proposed that it was a tetranucleotide(wrong) which each contained one of each nitrogen base. Many biologists believed his theory. Chargaff- % of adenine = % of thymine % of guanine = % of cytosine implied that A was always found with T and C was found with G Linus Pauling-determined the alpha helix of proteins but was trying to make a triple helix which obviously did not work

Rosalind Franklin was a graduate student working for Maurice Wilkins. She did the best X-ray diffraction studies but never got the credit.

5’end3’ end 5’ end strands are antiparallel

Crick

5’ 3’ phosphodiester bond

All 14 N All 15 N Mixture All DNA ½ DNA(½ 15 N DNA DNA 15 N ½ 15 N ½ 14 N) From bacteria From bacteria and ½ 14 N ½ 14 N DNA grown on 14 N grown on 15 N 14 N bacteria with bacteria with all for generations for generations DNA all 15 N DNA 15 N DNA grown grown on on 14 N for 2 light for one generations basic controls generation F 1 F 2

origin of replication topoisomerase helicase origin of replication topoisomerase RNA primers DNA ligase RNA

Telomerase is an enzyme that adds telomere repeat sequences to the 3' end of DNA strands. By lengthening this strand DNA polymerase is able to complete the synthesis of the "incomplete ends" of the opposite strand. Telomerase: is a ribonucleoprotein.ribonucleoprotein Its single snoRNA molecule — called TERC ("TElomere RNA Component") — provides an AAUCCC (in mammals) template to guide the insertion of TTAGGG.snoRNA Its protein component — called TERT ("TElomere Reverse Transcriptase") — provides the catalytic action. Thus telomerase is a reverse transcriptase; synthesizing DNA from an RNA template.reverse transcriptase Telomerase is generally found only in the cells of the germline, including embryonic stem (ES) cells; unicellular eukaryotes like Tetrahymena thermophila; some — perhaps all — "adult" stem cells and "progenitor" cells enabling them to proliferate;embryonic stem (ES) cells Tetrahymena thermophila"adult" stem cellsprogenitor cancer cells.

Telomeres