2.2. DNA Replication Flashcards
what are the universal features of replication?
(1) both DNA strands as template
(2) semiconservative mode of replication
(3) bidirectional synthesis
(4) 5’ to 3’ direction of synthesis
(5) specific base pairing
(6) requirement for RNA primer
explain how dna is reproduced by semi-conservative replication
each strand of the double helix serves as a template for a new strand. when the dna replicates, the two strands separate, and new complementary strands are synthesized for each of the original strands. as a result, each of the two new DNA molecules contains one original strand and one newly sythesized strand.
type of replication wherein the parent DNA molecule remains intact. after replication, one completely new double helix is created and the original helix is conserved
conserved replication
type of replication wherein the parental strands are dispersed into two new double helices following replication. hence, each strand consists of both old and new DNA
dispersive replication
discuss the meselson-stahl experiment
(1) e. coli is initially grown in a medium containing the heavy isotope 15N, resulting in DNA labeled with this heavier isotope
(2) the bacteria are then transferred to a medium with the lighter isotope 14N, causing newly synthesized DNA to incorporate the lighter nitrogen
(3) using cesium chloride density gradient centrifugation, DNA is separated based on density, revealing bands corresponding to different generations of DNA replication.
(4) after one generation, DNA showed a single band of intermediate density, which supports semi-conservative replication; each DNA molecule has one old (heavy) strand and one new (light) strand. however, it also reules out conservative replication, in which two distinct bands would occur
(5) after two cell divisions, DNA showed two bands: one intermediate and one lighter. similar results occurred after a third generation, except that the proportion of the lighter band increased. this was again consistent with the interpretation that replication is semiconservative.
what type of synthesis does DNA follow? explain.
bidirectional synthesis : creates two replication forks that move in opposite direction away from the origin of synthesis
formed by the juncture where the two strands separate
replication fork
true or false: in bidirectional synthesis, one replication fork is created.
false. two replication forks are formed in a bidirectional synthesis
segment of DNA that is replicated as a unit from a single origin
replicon
what are the two sites found in a replicon?
ori site and termination site
direction of DNA synthesis
5’ to 3’
a short segment of RNA complementary to DNA
RNA primer
design a 5-bp RNA Primers for the following DNA Sequences:
5’ GGGGCCCTCCTGAACG 3’
3’ CCCCGGGAGGACTTGC 5’
primer 1: 5’ CGUUC 3’
primer 2: 5’ GGGGC 3’
differentiate forward primer from reverse primer in polymerase chain reaction (PCR) primers
forward primer replicates the 3’ to 5’ template, whereas reverse primer replicates the 5’ to 3’ primer
PCR primer: identify forward and reverse primers given these strands
5’ GGGGCCCTCCTGAACG 3’
3’ CCCCGGGAGGACTTGC 5’
forward primer : GGGGC
reverse primer : CGTTC
major DNA replication enzyme in bacteria : replaces supercoils ahead of replisome
enzyme : DNA gyrase
encoding genes : gyrAB
major DNA replication enzyme in bacteria : binds origin of replication to open double helix
enzyme : origin-binding protein
encoding genes : dnaA
major DNA replication enzyme in bacteria : loads helicase at origin
enzyme : helicase loader
encoding genes : dnaC
major DNA replication enzyme in bacteria : unwinds double helix at replication fork
enzyme : helicase
encoding genes : dnaB
major DNA replication enzyme in bacteria : prevents single strands from annealing
enzyme : SSBP
encoding genes : ssb
major DNA replication enzyme in bacteria : primes new strands of DNA
enzyme : primase
encoding genes : dnaG
major DNA replication enzyme in bacteria : main polymerizing enzyme
enzyme : DNA polymerase III
encoding genes : n/a
major DNA replication enzyme in bacteria : loads Pol III onto sliding clamp
enzyme : clamp loader
encoding genes : holA-E
major DNA replication enzyme in bacteria : holds Pol III on DNA
enzyme : sliding clamp
encoding genes : dnaN
major DNA replication enzyme in bacteria : strand elongation
enzyme : polymerase subunit
encoding genes : dnaE
major DNA replication enzyme in bacteria : holds together the two core enzymes for the leading and lagging strands
enzyme : dimerization subunit (tau)
encoding genes : dnaX
major DNA replication enzyme in bacteria : proofreading
enzyme : proofreading subunit
encoding genes : dnaQ
major DNA replication enzyme in bacteria : excises RNA primer and fills in gaps
enzyme : DNA polymerase I
encoding genes : polA
major DNA replication enzyme in bacteria : seals nicks in DNA
enzyme : DNA ligase
encoding genes : ligA, ligB
major DNA replication enzyme in bacteria : binds terminus and blocks progress of the replication fork
enzyme : tus protein
encoding genes : tus