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AgingGenome
1. DNA damage2. Epigenetic shifts3. Telomere shortening
Organismal level1. Autoimmune, other defects in immune system2. Defective signaling
DNA REPLICATIONWC: DNA replication is semi-conservative
strands melt: form templates
for copy
Copy is reverse &complement of template
Copy of other strand
Meselson & Stahl
proved DNA replication is semi-conservative
1) grew E. coli on 15N to tell new DNA from old
• make dense DNA
Meselson & Stahl1) grew E. coli on 15N to tell new DNA from old• make dense DNA
2) Xfer to 14N
Meselson & Stahl1) grew E. coli on 15N to tell new DNA from old• make dense DNA
2) Xfer to 14N• new DNA is light
Meselson & Stahl1) grew E.coli on 15N totell new DNA from old• make dense DNA
2) Xfer to 14N• new DNA is light
3) measure of F1 & F2 DNA by centrifuging in CsCl
Meselson & Stahlmeasure of F1 & F2 DNA by centrifuging in CsClforms gradients when spun@500,000 x g
Meselson & Stahlmeasure of F1 & F2 DNA by centrifuging in CsClforms gradients when spun@500,000 x gDNA bands where is same as CsCl
Meselson & StahlResultsF0 DNA forms HH band
control Parental
Meselson & StahlF0 DNA forms HH band F1 DNA forms one higher band Control Parental F1
Meselson & StahlF0 DNA forms HH bandF1 DNA forms one higher band: HL Control Parental F1
Meselson & StahlF0 DNA forms HH bandF1 DNA forms one higher band: HL F2 DNA forms 2 bands: #1 same as F1#2 same as 14N DNA Control Parental F1 F2
Meselson & StahlF2 DNA forms 2 bands: # 1 same as F1#2 same as 14N DNA# 1 = HL# 2 = LL : DNA replication is semiconservative
DNA replication1) Replication begins at origins of replication
DNA replication1) Replication begins at origins of replicationPolymerases are dumb!
DNA replication1) Replication begins at origins of replicationDNA polymerases are dumb!other proteins tell where to start
DNA replication1) where to begin?2) “melting” DNA
DNA replication1) where to begin?2) “melting” DNA• must melt DNA @ physiological T
DNA replicationmust melt DNA @ physiological THelicase melts DNA
DNA replicationmust melt DNA @ physiological THelicase melts DNAForms “replication bubble”
DNA replicationhelicase melts DNAForms “replication bubble”
SSB proteins separate strands until they are copied
DNA replicationhelicase melts DNAunwinding DNA increases supercoiling elsewhere
DNA replicationhelicase melts DNAunwinding DNA increases supercoiling elsewhereDNA gyrase relieves supercoiling
DNA replicationDNA gyrase relieves supercoilingTopoisomerases : enzymes that untie knots in DNAType I nick backbone & unwind once as strand rotatesType II cut both strands: relieve two supercoils/rxn
DNA replication1) where to begin?2) “melting”3) “priming” • DNA polymerase can only add
DNA replication “priming”
DNA polymerase can only addprimase makes short RNA primers
DNA replication “priming”
primase makes short RNA primersDNA polymerase adds to primer
DNA replication “priming”
primase makes short RNA primersDNA polymerase adds to primer later replace primers with DNA
DNA replication1) where to begin?2) “melting”3) “priming”4) DNA replication
DNA replication4) add bases bonding 5’ P to 3’ OH @ growing end
DNA replication4) add bases bonding 5’ P to 3’ OH @ growing endTemplate holds next base until make bond
DNA replicationTemplate holds next base until make bond- only correct base fits
DNA replicationTemplate holds next base until make bond- only correct base fits- energy comesfrom 2 PO4
DNA replicationenergy comes from 2 PO4
"Sliding clamp" keeps polymerase from falling off
DNA replicationenergy comes from 2 PO4
"Sliding clamp" keeps polymerase from falling offProof-reading: only correct DNA can exit
DNA replicationProof-reading: only correct DNA can exit Remove bad bases & try again
DNA replication
Only make DNA 5’ -> 3’
Leading and Lagging StrandsOnly make DNA 5’ -> 3’strands go both ways!
Leading and Lagging StrandsOnly make DNA 5’ -> 3’strands go both ways!Make leading strand continuously
Leading and Lagging StrandsMake leading strand continuouslyMake lagging strand opposite way
Leading and Lagging StrandsMake leading strand continuously Make lagging strand opposite waywait for DNA to melt, then make Okazaki fragments
Leading and Lagging StrandsMake lagging strand opposite waywait for DNA to melt, then make Okazaki fragmentseach Okazaki fragment has its own primermade discontinuously
Leading and Lagging Strandseach Okazaki fragment has its own primermade discontinuouslyDNA replication is semidiscontinuous
Leading and Lagging Strandseach Okazaki fragment has its own primermade discontinuouslyDNA replication is semidiscontinuousOkazaki fragments grow until hit one in front
Okazaki fragments grow until hit one in frontRNAse H removes primer & gap is filled
Okazaki fragments grow until hit one in frontRNAse H removes primer & gap is filledDNA ligase joins fragments
Okazaki fragments grow until hit one in front
RNAse H removes primer & gap is filled
DNA ligase joins fragments
Energy comesfrom ATP-> AMP
DNA replicationReal process is far more complicated!Proteins replicating both strands are in replisome
DNA replicationReal process is far more complicated!Proteins replicating both strands are in replisome: feed DNA through it
DNA replicationProteins replicating both strands are in replisome: feed DNA through itlagging strand loops out so make both strands in same direction
lagging strand loops out so make both strands in same directionDNA pol detaches when hits previous primer, reattaches at next primer
Bacterial DNA has one originEuk have ARS ~ every 100,000 bp
- speed DNA replication
Euk have ARS ~ every 100,000 bp - speed DNA replication
ORC (Origin Recognition Complex) binds ARS
A B1 B2 B3
ORC binds ARSlicensing factors ensure each ARS is only replicated once/Sfall off when ARS is replicated, don't reattach until G1