11 BIO 326R DNA replication

11 BIO 326R DNA replication - BIO 326R DNA Replication...

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BIO 326R DNA Replication
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Basics Anti-parallel structure 5’ 3’ 3’ 5’ Replication is semi-conservative Daughter dsDNA will each have one old and one new strand 5’ 3’ 3’ 5’ 3’ 5’ 5’ 3’
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O N CH 2 PO 4 3’ 5’ O N N N O CH 2 PO 4 CH 2 PO 4 5’ 3’ 5’ 3’ PO 4 etc CH 2 PO 4
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Stages of Replication Initiation Specific site (Origin) selected, replication forks established Polymerization Movement of replication forks through chromosome Leading strand – continuous Lagging strand – dis continuous Termination Ends of DNA reached and “sealed” Separation of daughter chromosomes
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Initiation Replication starts at specific site (oriC in E. coli ) Origin binding protein (DNAa) – binds to and melts origin Approximately 20 DNAa proteins must bind to the oriC locus for replication to start Binding site for DNAa is a 9 bp sequence, so oriC is at least 180 bp long Origin must be fully methylated Nucleotides can be modified by adding a methyl (CH 3 ) group to the base (e.g. 7-methyl cytosine) In E. coli, the sequence GATC is recognized by the enzyme dam (D NA a denine m ethylase) which will add a methyl group to the A in the sequence Note that GATC is a palindrome – the complementary sequence to GATC is GATC Genome starts out “fully” methylated (both strands) Not all bases are modified, only at specific sites Daughter strands will not be methylated – Double stranded hybrid between methylated and non-methylated strands is called “hemi-methylated” DNAa will not bind hemimethylated DNA DNA methylase enzyme will later add methyl groups to daughter strand DNAa recruits other proteins to origin Helicase, DNA polymerase?
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protein GGGTTG A TCAATT CCCAACT A GTTAA GGGTTG A TCAATT CCCAACT A GTTAA GGGTTG A TCAATT CCCAACT A GTTAA Binding to fully methylated DNA Unwinding, initiation of replication GGGTTG A TCAATT CCCAACTAGTTAA GGGTTGATCAATT CCCAACT A GTTAA Replication: daughter strand(s) are made using dATP (no methyl group) Each ds DNA strand is hemimethylated Segregation of DNA to daughter cells
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11 BIO 326R DNA replication - BIO 326R DNA Replication...

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