Notes Ch. 5-8

Notes Ch. 5-8 - DNA Building blocks= phosphate, sugar, base...

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DNA Building blocks= phosphate, sugar, base Extends 5’ to 3’ w/ DNA synthesis, nucleoside triphosphate cleavage is GP/PP so one phosphate remains attached antiparalell other molecules can bind between strands, mostly in major groove Transformation principle- demonstrated by Griffith experiment, in which heat killed virulent strain transformed by nonvirulent strain- nonvirulent strain picks up pathogenic DNA Base pairings- A/T= 2 H bonds, G/C= 3 H bonds 1 turn of helix=10 base pairs Width of double helix=2nm, important for proofreading b/c helps in recognition of purine/purine or pyrimidine eq. base pairings Genes have the info to encode proteins Eukaryotic DNA is packaged into chromosomes exist in different forms throughout the cell cycle telomeres at end, centromere in middle pair=replicated chromosome single still attached=chromatid, but chromosome as soon as split occurs Interphase=genetic material more spread out. Heterochromatin=highly dense, ie at centromere. Euchromatin=more actively replicated/transcribed, more densely packed Genes are found on both strands of DNA DNA packing Nucleosome to 30 nm fiber Beads on a string Each chromatin bead is octameric, made up of four pairs of histone proteins: H2A, H2B, H3, H4 Not every eukaryote has h1 Mitotic chromosome is 10,000 times shorter than extended length of DNA Changes in nucleosome structure allow for DNA replication Chromatin remodeling driven by ATP, unwinds to allow for access to DNA strand Modifications to H3 tail: methylation= wind tighter, M-A=release nucleosome, P- A=gene expression
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Mechanism of DNA Replication Sequence of base pairs serves as origin of replication Usually in an A/T rich spot b/c AT base pairing has only 2 H bonds Origins of replication expand in both directions Triphosphate is cleaved to pyrophosphate With leading strand, you get smooth/continuous replication. With lagging strand, you get Okazaki fragments In Prokaryotes: There are 3 types of polymerase III is the main type used for DNA replication I is used for repair II is unknown Polymerase is self-correcting: 3’-5’ proofreading, exonuclease activity There are different sites for polymerization and proofreading on the same enzyme DNA polymerases cannot start synthesis from scratch Need RNA primer with 3’ hydroxyl group to initiate synthesis- laid down by primase Synthesis occurs up to old RNA primer, which is then excised and replaced by DNA RNA and DNA can’t bond because RNA still has nucleoside tri phosphate that not been cleaved by hydroxyl group Primers removed by polymerase I Ligase repairs nick in chain Sliding clamp mechanism keeps DNA polymerase attached to strand
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Notes Ch. 5-8 - DNA Building blocks= phosphate, sugar, base...

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