IT8 - DNA Replication Flashcards
(45 cards)
Does DNA polymerase alpha have proofreading activity? What is the consequence?
No, DNA polymerase alpha lacks proofreading activity, contributing to its relatively higher error rate (~10^-4).
Why is eukaryotic DNA polymerase alpha considered less suitable for highly processive DNA synthesis compared to Pol delta or epsilon?
DNA polymerase alpha lacks proofreading activity and has low processivity, meaning it synthesizes only short initial DNA (iDNA) segments before dissociating.
In what direction do DNA polymerases synthesise new DNA strands?
DNA polymerases can only replicate DNA in the 5’-3’ direction.
How does DDK specifically contribute to the activation of the CMG helicase complex?
DDK phosphorylates the MCM double hexamers, which leads to the recruitment of Sld3/7 and Cdc45.
What is the typical fidelity of eukaryotic DNA polymerases epsilon and delta?
Both DNA polymerase epsilon and delta have very high fidelity, with error rates typically less than 1 x 10^-9
When does helicase activation occur during DNA replication initiation, and what kinases are required?
Helicase activation occurs upon the formation of the CMG (Cdc45/MCM/GINS) helicase in S phase, requiring the activity of S-CDK and DDK kinases.
What mechanism limits the length of the initial DNA (iDNA) synthesized by DNA polymerase alpha to approximately 20 nucleotides?
Pol alpha specifically recognizes the A-form RNA/DNA helix of the primer-template and terminates synthesis upon the formation of B-form DNA after about two helical turns (approximately 20 nucleotides).
Differentiate the synthesis of the leading and lagging strands during DNA replication based on direction and continuity.
The leading strand is synthesised continuously in the direction towards the replication fork. The lagging strand is synthesised discontinuously in fragments away from the replication fork.
What two protein complexes are essential for ensuring the accurate segregation of the genome?
Cohesin and condensin are crucial for accurate genome segregation.
What are the two fundamental processes that underpin cell proliferation?
Error-free replication and accurate segregation of the genome underpin cell proliferation.
How does the short-range chromatin compaction mediated by histone modifications cooperate with condensin activity during mitosis?
This short-range compaction appears to cooperate with the long-range axial contraction of chromosomes mediated by condensins.
How is the newly synthesized RNA primer by primase efficiently transferred to DNA polymerase alpha for the initiation of DNA synthesis?
The PriL subunit of primase facilitates a direct molecular handoff of the nascent primer-template to DNA polymerase alpha.
What are some molecular determinants that influence replication timing during S phase?
Several firing factors are present in cells at levels well below the number of origins used. Their sequential action, potentially driven by differences in origin context, leads to the ordered firing of origins during S phase.
What is the typical action of eukaryotic replicative polymerases when they encounter a mismatched base during synthesis?
Excision of the mismatch by the polymerase’s proofreading activity is preferred over extending past the mismatch.
What are the roles of the PriL and PriS subunits of the primase enzyme?
PriL is the regulatory subunit that binds the template DNA. PriS is the catalytic subunit that initiates primer synthesis.
Besides topological entrapment, how else can cohesin interact with DNA loops?
Cohesin can also trap DNA loops in a non-topological manner in loop extrusion
What major challenge do cells face during chromosome segregation due to the properties of DNA?
The sheer size, physical properties, and number of DNA molecules create a significant topological challenge, primarily due to potential entanglements.
What term was introduced by Flemming to describe the nuclear substance in both resting and dividing cells?
The term chromatin was coined for this nuclear substance that is distributed throughout the resting nucleus and visible during nuclear division.
How is the length of iDNA synthesised by Pol alpha determined?
The length is determined by a counting mechanism: Pol alpha recognises the A-form RNA/DNA helix formed by the primer and terminates synthesis upon the formation of B-form DNA after about two helical turns.
What does DNA polymerase alpha synthesise immediately after the RNA primer, and what is its approximate length?
DNA polymerase alpha synthesises iDNA (initial DNA), which is approximately 20 nt long.
What protein stabilises single-stranded DNA during replication and interacts with the CMG helicase and Pol alpha/primase?
RPA (Replication Protein A) stabilises single-stranded DNA using its OB folds and interacts with the CMG helicase and DNA pol alpha/primase.
Based on Hi-C map analysis, what proteins are found to co-localise with high frequency interaction sites at the borders of topologically associating domains (TADs)?
High frequency interaction sites at TAD borders co-localise with cohesin and CTCF binding sites.
Which eukaryotic DNA polymerases are primarily responsible for leading and lagging strand synthesis, respectively?
DNA polymerase epsilon (ε) is associated with the leading strand, while DNA polymerase delta (δ) is associated with the lagging strand.
What is the approximate length of the RNA primer synthesised by primase?
RNA primers are typically about 10 nucleotides (nt) long.
