Bio3124 Lecture 8. Bacterial Genetics: I. Genome replication and packing. DNA Contains Cell Information. Total cell DNA = genome ( chromosome & extra-chromosomal ) Human genome = 4 billion bp 1000x as large as E. coli genome 90\% junk DNA
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Bacterial Genetics:I. Genome replication and packing
Winding more frequently
Winding less frequently
Supercoils twist DNA
Why supercoils are important?
Eubacteria => less frequent winding
Extreme thermophiles => more frequent windingSupercoiling Compacts DNA
Relieve torsional stress caused by supercoils
Act on one strand, How?
Type II Topoisomerases (DNA gyrase)
Introduce negative supercoils
Act on both strands of dsDNA, How?
Introduce positive supercoilsTopoisomerases Regulate Supercoils
E. coli oriC: 245 bp
SeqA binds to hemi methylated duplex at OriC
Full methylation following cell division and loss of SeqA affinity
DnaA concentration rises
Binds to 9-mer repeats at OriCReplication Begins at oriC
OriC: 245 bp contining 9-mer repeats, with 13-mer repeats in between
DnaA binding, strand melting at 13-mer by RNAP
DNA Pol III
DNA Pol III
Must add new base to 3OH of a chain
New nucleic acids grow to extend 3 endPolymerase Proceeds 5 3 on Each Strand