Download DNA Replication: Synthesis of Lagging Strand

Molecular Basis for
Relationship between Genotype and Phenotype
genotype
DNA
transcription
DNA sequence
replication
RNA
translation
protein
function
phenotype
organism
amino acid
sequence
Overview of DNA Synthesis
DNA polymerases synthesize
new strands in 5’ to 3’
direction.
Primase makes RNA primer.
Lagging strand DNA consists of
Okazaki fragments.
In E. coli, pol I fills in gaps in
the lagging strand and removes
RNA primer.
Fragments are joined by DNA
ligase.
DNA Replication at Growing Fork
DNA polymerases add nucleotides
in 5’ to 3’ direction.
Because of antiparallel nature,
synthesis of DNA is continuous for
one strand and discontinuous for
the other strand.
DNA Replication:
Synthesis of Lagging
Strand
Several components
and steps are involved
in the discontinuous
synthesis of the lagging
strand.
Note that DNA
polymerases move in 3’
to 5’ direction on the
template DNA
sequence.
DNA Replication:
Synthesis of Lagging
Strand
DNA extended from
primers are called
Okazaki fragments.
In E. coli, pol I removes
RNA primers and fills
in the gaps left in
lagging strands.
DNA ligase joins these
pieces.
Replisome and Accessory Proteins
pol III holoenzyme is a
complex of many
different proteins.
Refer to Figure 7-20 from Introduction to Genetic Analysis, Griffiths et al., 2012.
Looping of
template DNA
for the lagging
strand allows
the two new
strands to be
synthesized by
one dimer.
Priming DNA Synthesis
Primase enzyme
makes short RNA
primer sequence
complementary to
template DNA.
DNA polymerases can
extend (but cannot start)
a chain.
Primosome is a
set of proteins
that are involved
in the synthesis
of RNA primers.
Refer to Figure 7-20 from Introduction to Genetic Analysis, Griffiths et al., 2012.
DNA polymerase
extends RNA
primer with DNA.
Supercoiling results from separation of template strands
during DNA replication.
Helicases and
Topoisomerases
Helicase enzymes disrupt
hydrogen bonding between
complementary bases.
Single-stranded binding
protein stabilizes unwound
DNA.
Unwound condition
increases twisting and
coiling, which can be
relaxed by topoisomerases
(such as DNA gyrase).
Topoisomerases can either
create or relax supercoiling.
They can also induce or
remove knots.
Chromatin assembly factor I (CAF-I) and
histones are delivered to the replication fork.
CAF-I and histones bind to proliferating cell
nuclear antigen (PCNA), the eukaryotic version
of clamp protein.
Nucleosome assembly follows thereafter.
Refer to Figure 7-23 from Introduction to Genetic Analysis, Griffiths et al., 2012.
Overview of DNA Synthesis
DNA polymerases synthesize
new strands in 5’ to 3’
direction.
Primase makes RNA primer.
Lagging strand DNA consists of
Okazaki fragments.
In E. coli, pol I fills in gaps in
the lagging strand and removes
RNA primer.
Fragments are joined by DNA
ligase.
Initiation at Origin of Replication
Prokaryotes:
Fixed origin
DnaA proteins
DnaB (helicase)
Eukaryotes:
Multiple origins
ORC protein complex
Cdc6 and Cdt1
MCM complex (helicase)