DNA replication Flashcards
DNA replication is
semi-conservative
Semi-conservative
each daughter double helix contains one template strand and one newly synthesized strand
protein involved in replicating double-stranded DNA
DNA polymerase
Challenges in DNA replication
synthesis of two new daughter strands goes in opposite directions
how to unwind and separate the two parental strands
how to protect unwound portions from attack by nuclease
how to prevent errors in replication
Negative supercoiling of chromosomal DNA makes it
underwound
Underwinding DNA makes it
easier for the individual strands to be separated
Two strands of DNA are separated by
hexameric helicase
Volu=nerability of single-stranded DNA is defended by
Single stranded DNA binding domains (SSBs)
SSB in eukaryotes
protein A
DNA double helix unwinds at a specific point called
origin of replication
At each origin of replication, there are
two replication forks
According to the factory model of replication
protein machinery is stationary and DNA moves through it
Leading strand
synthesized continuously from 5’ to 3’ end at the replication fork on the exposed 3’ to 5’ template strand
lagging strand
synthesized semidiscontinously in small fragments or Okazaki fragments
Fragments of the lagging strand are linked together by
enzyme- DNA ligase
Prokaryotic DNA polymerases
DNA Pol I
DNA Pol III
DNA Pol II
DNA Pol I does what
repair and patching of DNA
DNA Pol III does what
main enzyme for synthesizing new DNA strand
DNA Pol II does what
proofreading and repair enzyme
DNA gyrase
relieves positive supercoils and relieves torsional strain
Helicase
unwinds DNA helix and causes strand to separate
SSB
stabilizes single stranded regions and prevents reannealing of DNA
Primase
synthesizes the RNA primer
DNA ligase
seals nicks in DNA
DNA Pol I
removes the RNA primer
DNA Pol III
responsible for new strand synthesis
Pol
abbreviation for polymerase
DNA gyrase is considered a
type II topoisomerase
DNA gyrase creates a _____ in relaxed circular DNA relieving the supercoiling
nick
Energy for DNA gyrase to do its job is provided by
hydrolysis of ATP to ADP and Pi
what serves as a primer in DNA replication
RNA
Primase uses the DNA template strand to
produce RNA primer sequence
Newly formed DNA is linked to the
3’-OH of the RNA primer
Okazaki fragments are formed on the lagging strand due to
the requirement for DNA synthesis in the 5’ to 3’ direction
As the replication fork moves away, the RNA primer is removed by
DNA polymerase I
____ makes the final covalent bond between Okazaki fragments
DNA ligase
DNA synthesis is bi-
directional
DNA replication occurs during the
S phase
Errors in DNA replication cause
mutations
Errors in replication spontaneously perhaps once in
10^6 base pairs
Proofreading reduces errors to once in
10^10 base pairs
Proofreading involves the removal of
nucleotides immediately after they are added to the growing DNA strand during replication
3’-5’ exonuclease activity of DNA Pol does what
removes incorrect nucleotides during DNA synthese
Mutagens
agents that bring about a mutation
Thymidine dimers
dimerization of adjacent thymidine caused by UV light
Modified bases that cannot be directly repaired can be
removed and replaced
