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Lecture 6

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Biology 1001A
Tom Haffie

Lecture 6: Genome Replication What is your DNA doing? - 3 billion base pairs - Mistake: researchers defined functional as anything that looks like it can be expressed o Belief that 80% of the genome is “functional”  However, junk DNA = helpful evidence for evolution - How does DNA get replicated? - What is a fork? - What is a replication bubble? - What to do with the ends of the DNA strands? Double helical structure of DNA with two antiparallel backbones  DNA Structure - A distinct 3’ and 5’ end confers “polarity” on each of the DNA backbones. - 3’ has free hydroxyl (OH) - 5’ has free phosphate - Two strands of double helix run “antiparallel” Replication is semi-conservative - Replication fork - Know of Meselson and Stahl experiment – DNA replication is semi-conservative - New chain added on 3’ end  leading strand - Original 5’ end  lagging strand - Every DNA polymerase only does one form of elongation and elongates 3’ ends DNA polymerase adds to a free 3’OH  Replisomes (proteins together) replicate one strand continuously, one discontinuously - REPLISOMES – active at the replication fork - Contains 2 molecules of DNA polymerase – 2 replisomes working simultaneously - Can only extend 3’ end - Parent strands are anti-parallel - Replication starts from the sole origin - Sends replication forks on either sides - Bi-directional - RESULT: replication bubble Replication bubble is just two forks - Primers provide 3’ polymerase to the chains - Prokaryote genomes are usually small - Can replicate from one replication bubble - Humans way more complex – need many more origins - Replication “bubble” arises from two “forks” created at one “origin” Large, linear, eukaryotic chromosomes fire several origi
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