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28 Cards in this Set
- Front
- Back
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How many base pairs do humans posses (Homo sapiens) |
3000 millions of bp of DNA |
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Experiment from Griffith, Avery, McCarty, MacLeod (1944) (3) |
-DNA could transform one type of bacteria into another type -streptococcus pneumoniae (two types: smooth and rough) -smooth have capsule that kill mice -> heat killed s cells transformed r cells into s |
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Experiment from Hershey and Chase (1952) (4) |
-DNA, not protein is the infectious agent -Bacteriophages are virus that infect bacteria -bind to surface of bacterium and inject DNA -detected via sulphur (protein) and phosphate (DNA) radioactivity |
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Experiment from Meselson and Stahl (late 1950's) |
-semi-conservative replication of DNA -non-radioactive isotopes of nitrogen were used in this experiment -can be distinguished after 2.replication |
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when does DNA replication occur? (2) |
when a cell divides
when two cells fuse |
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Sister Chromatid staining shows.. |
SCE = Sister chromatid exchange cultivation with bromdesoxyuridine (BrdU) |
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DNA Replication is directional |
cellular proofreading and error-checking mechanisms in one direction one replication fork |
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DNA Replication is bidirectional |
in two directions one origin two replication forks |
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Rate of Replication in E.coli |
base pairs/minutes/60sec. = bp/second 4639221bp/42min/60sec = 1840bp/sec. E.coli divides faster than replication would occur because of multiple real. forks "firing" |
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Rate of Replication in humans |
100 bp/s per fork forks are only active for part of the required time |
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DNA Replication: Important points |
-DNA polymerase cannot melt or unwind duplex DNA -DNA polymerase cannot initiate chains -DNA polymerase can extend pre-existing DNA/RNA chains -can only start at origin of replication -strands grow in 5' - 3' direction |
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helicase (E. coli) |
DnaB is composed of six identical subunits (hexamer) cannot find origin of replication |
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oirigin of replication (oriC) (E. coli) |
specific sequence where DnaA binds to |
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DnaC.. (E. coli) |
..delivers DnaB to template |
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pre-priming complex
(E. coli) |
one DnaB hexameter clumping around each single strand |
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consensus sequence (yeast) |
ARS = autonomously replicating sequence |
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Process: UNWINDING (E. coli) |
-DnaA binds to oriC -> open complex -DnaB finds this complex (delivered by DnaC), unwinds DNA -pre-priming complex is formed -DnaB moves along strand unwinding it, needs ATP -single strand binding protein (SSB) prevents strands from reannealing |
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Process: PRIMING (E. coli) |
-DnaG binds -forms primosome -synthesizes a short RNA primer on each strand -DnaG dissociates -DNA polymerase can bind |
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DnaG (E. coli) |
= RNA polymerase primase does priming joins RNA nucleotides into primer |
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primosome (E. coli) |
complex formed with DnaG |
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DNA Replication is asymmetric.. |
.. one continuous/leading strand and one discontinuous/lagging strand 5' to 3' direction |
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Process: DNA REPLICATION |
= copying DNA DNA polymerase III adds DNA nucleotides to primer (elongation) RNA primer is removed and replaced with DNA by another DNA polymerase ( I ) |
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Process: REPLICATION ON LAGGING STRAND |
overall direction: 3' to 5' of lagging strand nucleotides added in 5' to 3' direction into smaller fragments (Okazaki fragments) nicks ligated by ligase (traveling in overall direction) needs: multiple RNA primers 2 DNA polymerases (1x 3'-5' exo) DNA ligase |
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dNTP's |
deoxynucleoside triphosphate |
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ligase-defective mutant cells |
high number of okazaki fragments with small size |
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Process: EXTENSION |
??? |
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TOPOISOMERASES |
maintain proper helical density untangle finished chromosomes type I topoisomerase: relax DNA by nicking and closing one strand of duplex DNA E.coli type I topoisomerase (Topo I): removes negative supercoils -> maintain density type II topoisomerase: change DNA topology by breaking and rejoining double-stranded DNA E.coli type II topoisomerase (DNA gyrase, Topo II): introduces negative supercoils at oriC |
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DNA B - helices needs ... |
... ATP !! |
