Exam 2- DNA replication Flashcards
(T/F) Synthesis of the leading and lagging strands requires a primer only at the start of replication
false
true for leading strand but the lagging strand requires a new primer for every Okazaki fragment that is synthesized
(T/F) Base-paired primers consist of RNA that are synthesized by an enzyme
true
_______ the enzyme that synthsizes base-paired primers
DNA primase
____ used by DNA primase to synthesize short RNA primers
ribonucleoside triphosphates (ATP,CTP,GTP, UTP)
which of the ff does not apply to primers?
a. about 10 nucleotides long in eukaryotes
b. are made every 100-200 nucleotides along the lagging strand
c. has a free 3’OH group at its end used to initiate DNA synthesis
d. removed by RNAse H
none of the above, all applies :)
(T/F) In prokaryotes, Pol I removes the RNA primer and replaces it with dNTP’s
true
_____ enzyme that seals adjacent lagging strand fragments
DNA ligase
(T/F) cells use RNA primers to mark these initial (error) sequences as potentially inaccurate regions of new strands that must be replaced with correct complementary sequences
true
(T/F) enzymes capable of initiating synthesis of new DNA strands can correct their own base-pairing errors
false
would not be efficient at correcting their own base-pairing errors
______ are the proteins involved in the separation of the parental complementary strands
DNA helicases and Single-strand DNA binding proteins (SSB proteins)
____ the enzyme that functions to to pry apart double helix
DNA helicase
(T/F) DNA helicase does not require the use of energy to carry out its function
false
uses energy derived by hydrolysis of ATP to change its shape and migrate along a DNA single strand
(T/F) type of helicase that runs along the lagging strand seems to play the major role in separating the DNA strands
true
____ the structure of helicase
hexameric (6 subunits)
(T/F) do not unwind duplex but rather assist helicase by stabilizing unwound single stranded DNA
true
(T/F) aside from stabilizing the unwound DNA, helix-destabilizing proteins also function to straighten single stranded DNA of the leading strand template to prevent the formation of hairpin loops (DNA folding back on itself)
false
it does this to the LAGGING strand
____ are formed when DNA folds back on itself to self-hybridize block the movement of DNA polymerase during DNA synthesis
hairpin loops
which of the ff does not apply to single stranded binding proteins?
a. blocks hairpin formations
b. covers the bases when bound to DNA
c. prefer to bind next to previously bound molecules along a DNA strand
d. does not unwind the DNA strands
B
exposure of bases needed for base-pairing is not blocked by protein binding
_____ keeps Pol III attached to DNA during polymerization
Accessory (sliding) Clamp-Like Protein
Beta subunit of pol III in bacteria
which of the ff does not apply to sliding clamp proteins?
a. assembly requires GTP
b. its assembly is mediated by the clamp loader complex
c. Ring slides freely over single stranded DNA
d. released from DNA when it runs into DNA double strands
A
requires ATP
____ human version of E. coli clamp protein
proliferating cell nuclear antigen (PCNA)
*(T/F) in both the lagging and leading strands, Pol remains associated with clamp protein for long distance
false
this applies only to leading strand
*(T/F) on lagging strand, Pol and its associated clamp protein are released each time they reach the 5’ end of an adjacent Okazaki fragment then cycle back to the next RNA primer to synthesize another Okazaki fragment
true
____ a complex formed in prokaryotes when the helicase is directly linked to the primase on the lagging strand
primosome
(T/F) The primase is driven by the helicase along the lagging strand, producing the RNA primers needed for each successive Okazaki fragment
true
_____ the size of the major replicating protein complex
greater that 10^6 daltons in MW
(T/F) lagging strand loops back in such a way that both the leading and lagging strands can be synthesized by the same replication protein complex
true
(T/F) the pol of the of the lagging strand is associated with the large protein complex, and cannot be reused to synthesize each successive Okazaki fragment
false
it can be reused!
_____ are enzymes that regulate the supercoiling of DNA and prevent its tangling during replication (controls topology, or geometric configuration of DNA)
DNA topoisomerases
(T/F) DNA must be unwound ahead of replication fork by topoisomerases to permit movement of DNA polymerase
true
____ the speed at which the DNA helix ahead of the replication fork rotates
50 revolutions/sec
_____ the speed which the a replication fork moves
at 500 nucleotides/sec
______ the topoiomerase that produces transient single-strand breaks in the DNA along the phosphodiester backbone
type I topoisomerase
_______ the topoisomerase that generates transient double stranded breaks in DNA that can permit one DNA duplex to pass through another duplex
type II topoisomerase
(T/F) type II topoisomerase permits one strand of DNA to swivel relative to the other and thus relieve tension in the DNA during replication
false
this is type I
(T/F) DNA gyrase is situated ahead of the replication fork to unwind DNA and permit passage of DNA polymerase
true
which of the ff topoisomerases breaks the DNA strand by forming a covalent bond between a tyrosine in its active site and a DNA phosphate?
a. Type I topoisomerase
b. Type II topoisomerase
A
which of the ff topoisomerases functions to detangle chromosomes?
a. Type I topoisomerase
b. Type II topoisomerase
B
(T/F) type II topoisomerase uses energy from the hydrolysis of ATP to break permanently both strands of one DNA helix and then pass a second helix through the break
false
break transiently
(T/F) type II topoisomerase reseals the double stranded break before dissociating from the DNA
true