Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies DNA Replication

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies DNA Extraction Go to this website and work through the tutorial traction/

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Websites hill.com/sites/ /student_view0/ch apter14/animations.html# hill.com/sites/ /student_view0/ch apter14/animations.html# romboneFinald.swf romboneFinald.swf chp11/ html chp11/ html

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies When does DNA Replication occur? Right before cell division (S phase of interphase)

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Cell Cycle

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Review of DNA Structure Double stranded (antiparallel) Nucleotide  Phosphate  Deoxyribose sugar  Nitrogen base - Adenine - Thymine - Cytosine - Guanine

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Phosphodiester Bond – add nucleotides to 3’ end

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Chromatin vs Chromosomes

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Big question Do the 2 strands stay together or apart after DNA replication?

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies 3 options

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Meselson-Stahl Experiment

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Semi-Conservative Replication Each chain in the helix is a complimentary mirror image of the other.  Double helix unzips and undergoes semi-conservative replication, meaning each strand of the original duplex becomes the template of another duplex; original molecule is not conserved

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Replication Process 1. Splitting of the 2 strands 2. Priming of the DNA strand 3. Synthesis of new DNA strands 1. Leading strand – continuous 2. Lagging strand - discontinuous 4. Replacement of RNA primers 5. Joining of any gaps in the strands created during DNA replication

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Vocabulary Template – DNA strand used to make the complementary strand

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Splitting of the 2 strands

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Helicase – unwinds DNA double helix, breaks the H bonds between strands Single stranded binding proteins (SSB’s) – bind to unwound double helix to prevent reannealing (re-winding) Topoisomerase – cuts and rejoins DNA behind replication fork to release tension built up (think pulling 2 ropes apart that are intertwined) Replication fork – site of DNA uncoiling

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Origins of replication Prokaryotic – 1 origin Eukaryotic – multiple origins

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Priming

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Primase – RNA polymerase puts down a RNA primer to initiate DNA replication (DNA polymerase III cannot synthesize new strands – has to have something to add on to)

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Synthesis of Leading Strand

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Leading Strand Synthesis DNA Polymerase III adds DNA nucleotides to the 3’ end of the RNA primer DNA polymerase III reads in the template strand in a 3’ to 5’ direction Writes the complementary DNA strand in a 5’ to 3’ direction Leading strand moves in the direction of the replication fork DNA replication on the leading strand is continuous

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Synthesis of Lagging Strand

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Lagging Strand Moves away from replication fork DNA polymerase III still writes in a 5’ to 3’ direction Primase puts multiple RNA primers down on the lagging strand DNA polymerase III fills in the gaps DNA strand fragments are called Okazaki Fragments DNA replication on the lagging strand is semidiscontinuous

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Replacement of RNA Primers/Joining of Okazaki Fragments

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Repairing of Gaps in the DNA strand DNA Polymerase I – removes RNA primers, fills in gaps with new DNA nucleotides DNA ligase – repairs nicks in the DNA (missing phosphodiester bonds), between Okazaki fragments

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Problem with DNA Replication

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Telomeres At the end of the DNA strands, there is not enough room to “prime” the Okazaki fragment Incomplete ends of the chromosome are created Telomeres are repeating sequences of DNA (TTAGGG) on the ends of chromosomes that do not code for protein (they do however protect the chromosome ends from damage)

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies

Aging Telomerase – enzyme that helps prevent degradation of telomeres by adding TTAGGG sequences at the end of chromosomes (elongate the telomeres)  Activated in fetal cells, adult germ cells (gametes), and tumor cells  Somatic (body) cells do not have an activated telomerase gene, chromosomes shorten after repeated rounds of DNA replication, causes cells to age (causes body to age)

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Cancer Cells Since cancer cells divide uncontrollably, the telomeres should eventually get to short to sustain the cell’s life (the cell would age to quickly and die) Typically have a mutation in the gene that blocks telomerase activity (activates telomerase to elongate telomeres) Scientists think if they can study telomerase more, they may find the key to finding a cure for cancer Scientists have stopped telomerase activity in certain cancer cells causing them to die

Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies Protein Synthesis Practice