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Questions and Answers
Which of the following best describes the function of an initiator protein in DNA replication?
Which of the following best describes the function of an initiator protein in DNA replication?
- It synthesizes RNA primers to provide a free 3'-OH group for DNA polymerase.
- It identifies and binds to a specific DNA sequence within the replicator, initiating replication. (correct)
- It prevents premature termination of replication by stabilizing the replication fork.
- It unwinds the DNA double helix at the origin of replication using ATP hydrolysis.
In the context of DNA replication, what distinguishes a 'replicon' from a 'replicator'?
In the context of DNA replication, what distinguishes a 'replicon' from a 'replicator'?
- A replicon contains the cis-acting DNA sequences sufficient to direct the initiation of DNA replication, while the replicator is the entire region replicated from a particular origin.
- A replicon is all the DNA replicated from a particular origin of replication, and the replicator is the cis-acting DNA sequence that directs the initiation of DNA replication. (correct)
- A replicon refers to the location where termination occurs, whereas the replicator indicates the starting point of replication.
- A replicon is the protein responsible for unwinding DNA, while the replicator is the DNA sequence it binds to.
How does the process of assembling a pre-replication complex (pre-RC) contribute to the regulation of DNA replication in eukaryotes?
How does the process of assembling a pre-replication complex (pre-RC) contribute to the regulation of DNA replication in eukaryotes?
- It directly inhibits the activity of telomerase, preventing telomere elongation and cellular immortalization.
- It actively degrades any improperly formed replication forks to maintain genomic stability.
- It prevents the assembly of new origins of replication near the original one, ensuring even coverage across the genome.
- It ensures that each origin of replication is activated only once per cell cycle, preventing over-replication. (correct)
What is the primary function of telomere binding proteins in maintaining genomic stability?
What is the primary function of telomere binding proteins in maintaining genomic stability?
Considering both prokaryotic and eukaryotic DNA replication, which of the following mechanisms is unique to eukaryotic replication termination?
Considering both prokaryotic and eukaryotic DNA replication, which of the following mechanisms is unique to eukaryotic replication termination?
Flashcards
Origin of Replication
Origin of Replication
Specific sites where DNA unwinding and replication begin.
Replicon
Replicon
The entire DNA segment replicated from a single origin of replication.
Replicator
Replicator
DNA sequences that instruct where to begin replication.
Initiator Protein
Initiator Protein
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Telomerase
Telomerase
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Study Notes
- Initiation of DNA replication starts with the replicon model
The Replicon Model of Replication Initiation
- Origin of replication refers to the specific sites where DNA unwinding and initiation of replication occur
- Replicon refers to all of the DNA replicated from a particular origin of replication
- Replicator is the cis-acting DNA sequences sufficient to direct the initiation of DNA replication
- Initiator is the protein that specifically recognizes a DNA element in the replicator; activates the initiation of replication
Replicator Sequences
- Replicator sequences include initiator-binding sites and easily unwound DNA
- oriC (E. coli) includes:
- Thirteen 13-mer sites
- Nine 9-mer sites
- 245 bp
- SV40 includes:
- EP EP P P P P
- 65 bp
- S. cerevisiae includes:
- B2 B1 A
- 100 bp
Function of Replication Machinery in Prokaryotes
- DnaA-ATP binds to 13-mer and 9-mer sites
- DNA helicase (DnaB) and DNA helicase loader (DnaC) are implemented
- Primase is used to initiate the replication process
Regulation of DNA Replication in Prokaryotes
- Regulation involves coordinating the initiation of replication
- Dam methylase either adds or removes methyl groups to regulate initiation
- SeqA binds to hemimethylated GATC sequences
Multiple Replicators in Eukaryotes
- Multiple replicators initiate replication at different sites in eukaryotes
- Origins 3 and 5 initiate replication together
- Origin 1 initiates replication before origin 2, which is passively replicated
- Origin 4 is passively replicated
Assembly of Pre-Replication Complex in Eukaryotes
- ORC binds to replicator DNA
- Cdc6 binds to ORC
- Mcm2-7 and Cdt1 bind
Activation of Helicase and Assembly of Eukaryotic Replisome
- Mcm2-7 is activated by Sld2, Sld3, and Dpb11
- CDK and DDK are required to activate Pol E, GINS, and Cdc45
Regulation of DNA Replication in Eukaryotes
- In the G₁ phase (loading phase), helicase loading is allowed; helicase activation is not allowed
- In the S, G₂, and M phases (activation phase, new helicase loading is inhibited; helicases are activated
- During the loading phase CDK levels are low in G1
- During the activation phase CDK levels are high in S
Replication Termination in Prokaryotes
- The termination of replication in prokaryotes is completed by topoisomerase II
Replication Termination in Eukaryotes
- In eukaryotes, replication termination involves the repair of Okazaki fragments
- Incomplete replicated DNA is replicated again, which results in telomeres being shorter
Protein Priming
- Allows DNA polymerase to use a protein as a primer, initiated from the 3' end
Telomerase
- Telomerase synthesizes new DNA using an RNA template
Telomere Binding Proteins
- In Yeast: Rif2, Rif1, Rap1, Cdc13, and other proteins
- In Humans: TIN2, TPP1, POT1, TRF1, TRF2, Rap1, and other proteins
- Telomere binding proteins bind to the end of the telomere
T-Loop Formation
- Folding of the telomeres allows strand invasion and protects it from damage
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Description
Explanation of the replicon model for DNA replication initiation. Covers origin of replication, replicons, replicators, and initiators. Key sequences in E. coli, SV40, and S. cerevisiae are also mentioned.
