2_Replication_Classnotes

2_Replication_Classnotes - 1/23/07 Replication...

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1/23/07 Replication Semiconservative model of DNA replication S emiconservative replication - Parent strands separate o One parent template in each daughter cell - old template pairs with a new - true model Conservative replication - both parent templates goes to one daughter cell - 2 new templates are created for 2 nd daughter cell * Prokaryotes have no nuclear envelope, so DNA is easily accessible - E. coli is the most common prokaryote * Eukaryotes have a nuclear envelope - Includes plants, animals, fungus, and protist Replication in E. coli , geneticists’ favorite prokaryote Origin of Replication contains 2 things: 1) DnaA Box - binding site for protein called DnaA - clump of DnaA bends the clump of DNA 2) AT-rich region - easier to separated because it only has 2 hydrogen bonds > GC base pairs have 3 hydrogen bonds - located between the leading and lagging strand when its splitting (replication bubble) Helicase – enzyme used to separate the doubled-stranded DNA - found at both replication forks - 3 Terms for strand separation of DNA: melt with heat unwind denature 1/25/07 Topoisomerases - breaks the phoshodiester bond - untwists the DNA strands - the reconnects the same phosphodiester bond that it broke earlier Replication Fork – Added nucleotide must have 3 phosphate groups on it (deoxyribonucleoside TRIphosphate ) 2 AAGCGGTCA AAGCGGTCA TTCGCCAGT AAGCGGTCA TTCGCCAGT AAGCGGTCA TTCGCCAGT TTCGCCAGT AAGCGGTCA TTCGCCAGT AAGCGGTCA TTCGCCAGT AAGCGGTCA TTCGCCAGT
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- it loses the last 2 once it attaches to the template strand - The phosphate of the 5’ of the carbon of the added nucleotide must attach to the 3’ end (3’ carbon OH) of the growing strand, creating a new phosphoester bond Adding new nucleotides is in regards to the direction of synthesis of the template strand: 3’ old to 5’ old. - new nucleotides can only be added to old strands RNA polymerase initiates the synthesis by working with: - Primase – the enzyme that makes the primer (shown by squiggles) primers are usually about 10 nucleotides long, which is really short compared to the strand takes RNA nucleotides and puts them together and moving in a 5’ to 3’ direction consecutively (5’ 3’ RNA polymerase activity) This process has LOW PROCESSIVITY (start, stop, start, stop, short time) It only needs to stay in place until a DNA polymerase attaches to it Most important thing a primer gives us is a 3’ end for DNA polymerase to add on new nucleotides
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2_Replication_Classnotes - 1/23/07 Replication...

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