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Lecture 6

Biology 1001A 2012 Lecture 6 & 7 Notes.docx

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Western University
Biology 1001A
Tom Haffie

Lecture 6: Genomic Replication 10/18/2012 1:28:00 AM  DNA Structure  Components: 5-carbon deoxyribose sugar, nitrogenous bases, and phosphate groups linked by covalent bonds  Two strands of DNA held together in a double helix by hydrogen bonds between the nitrogenous bases and run antiparallel to each other  Purine-Pyrimidine complimentary base pairing: adenine bonds to thymine, guanine bonds to cytosine  Each strand has a distinct 3’ and 5’ end (referring to a carbon atom in the deoxyribose sugar)  3’ has a free hydroxyl (OH) group  5’ has a free phosphate group   DNA Replication  Replication is semi-conservative and semi-discontinuous  A replisome includes all the enzymes involved in DNA replication  DNA is read 3’ to 5’ and replicated 5’ to 3’; DNA Polymerase can only extend the 3’ end  leading strand is replicated continuously, lagging strand is replicated discontinuously  Circular prokaryotic DNA creates two replication forks (a replication bubble) that travel in opposite directions -> bi-directional  Linear eukaryotic DNA is often much larger, so several origins are fired simultaneously from which replication bubbles begin constructing new DNA; makes DNA replication much faster  DNA Polymerase cannot complete the lagging strand, as there is no 3’ end to extend; this would mean DNA would shorten every time it replicated; Telomerase solves this problem  Telomerase binds to the original DNA strand and using its own RNA, extends the 3’ end of the original strand before separating  DNA Polymerase can then complete the replication by extending the
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