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Lecture 6

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Biology 1001A
Tom Haffie

 Genome Is full of “junk” DNA  Misunderstanding because researchers defined “functional” as anything that looks like it could be expressed  It might be functional, but it’s not function to make you  Double helical structure of DNA with two antiparallel backbones  Each single strand of DNA has a 3’ and 5’ end which confers “polarity” on DNA backbones and gives it a sort of “direction”  3’ end has a free hydroxyl (OH)  5’ end has a free phosphate  Two strands of double helix run antiparallel  Replication is semi-conservative -> know Meselson & Stahl  DNA polymerase adds incoming nucleotide to a free OH on the 3’ end of the DNA  Every DNA polymerase does only one kind of elongation: extends the 3’ end  Replisomes replicate one strand continuously, one discontinuously  Replisomes are active at the replication fork  Two polymerase are going simultaneously to extend the two strands  However you can only go from the 3’ end, but the strands of parent DNA are antiparallel; thus going in different directions  Requires that the replisome extends one end continuously and the other discontinuously  Replication is semi-conservative and semi-discontinuous  A replication “bubble” arises from two forks created at one “origin”  Semi-conservative, semi-discontinuous and bidirectional in prokaryotic cells  This creates a replication bubble  Need to know how to draw the structure of a bubble! Put in the primers, okasaki fragments, 3’ & 5’, origin -> what is the structure of a bubble (slides 10&11 in ppt)  Replication bubble is just 2 forks; RNA primers make a 3’ end for polymerase to extend  DNA polymerase cannot create, can only extend  Can’t replicate your genome from one origin  DNA replicates quickly because it has multiple origins; forks going in different directions  Large, linear, euk chromosomes fire several origins simultaneously  Know what the enzymes do, the basic structures; how does what you know about a fork translate into bubbles & replicating whole chromosomes & whole genomes  Chromatids are identical DNA molecules attached at their centromeres  G1 & the S phase is where DNA replicates,  In g2, it’s composed of 2 molecules of DNA  Once they condense a lot, they become a double stranded chromosome like in metaphase  Make that connection between DNA replication and chromosomes/chromatids  Unreplicated chromosome: one chromosome
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