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What is the primary function of DNA polymerase I?
Which activity of DNA polymerase I is responsible for proofreading newly synthesized DNA?
How does DNA ligase contribute to DNA replication?
What is the error rate of DNA replication, according to the content?
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What is a key characteristic of the mismatch repair mechanism?
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What initiates DNA replication in eukaryotes?
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What is the role of the MCM factor in eukaryotic DNA replication?
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What is a characteristic feature of translesion DNA polymerases?
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What would be the consequence of one error per million base pairs during DNA replication?
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Which model of DNA replication suggests that one strand remains completely intact while the other is newly synthesized?
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In Meselson and Stahl's experiment, what type of nitrogen media did E.coli first grow in?
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What is the main characteristic of the semiconservative replication model?
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Which replication mode involves a replication fork and is typically bidirectional?
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What is the primary characteristic of discontinuous replication?
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What is the role of replicons in DNA replication?
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Which enzyme is primarily responsible for synthesizing the RNA primer during DNA replication?
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What do Meselson and Stahl’s results contradict regarding the conservative model?
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What is the role of DNA polymerase III in DNA replication?
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Which protein is responsible for unwinding the DNA helix during replication?
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Which of the following statements is true regarding DNA replication speed in E.coli?
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What is the significance of the 3′-OH group in DNA replication?
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How does DNA polymerase I contribute to DNA replication?
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Which component is essential for the formation of the replication bubble at the origin of replication?
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What role does DNA ligase fulfill during DNA replication?
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What is required for the formation of new nucleosomes following DNA replication?
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What role does telomerase play during DNA replication?
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What would most likely occur if an organism's telomerase were mutated to be nonfunctional?
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How does DNA replication in eukaryotic cells differ from that in bacteria?
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Which statement accurately describes the location of DNA replication in eukaryotic cells?
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What is a primary consequence of the end replication problem in linear chromosomes?
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Which component is NOT involved in the extension of telomeres during DNA replication?
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What happens to nucleosomes immediately after DNA replication?
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What is the main feature of theta replication in bacteria?
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Which of the following requirements is NOT needed for linear eukaryotic DNA replication?
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In which direction do DNA polymerases add nucleotides during DNA synthesis?
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What characterizes the replication fork during eukaryotic DNA replication?
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What is a significant characteristic of rolling-circle replication?
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How many origins of replication are typically found in linear eukaryotic DNA?
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What type of DNA replication occurs in a semiconservative manner?
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Which component is critical for the phosphodiester bond formation in DNA replication?
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Study Notes
Eukaryotic DNA Replication
- Similar to bacterial replication, but differs in several aspects
- DNA is complexed with histone proteins in nucleosomes
- Nucleosomes quickly reassemble following replication
- Creation of nucleosomes requires:
- Disrupting original nucleosomes on the parental DNA
- Redistributing pre-existing histones on the new DNA
- Adding newly synthesized histones to complete the formation of new nucleosomes
Location of Eukaryotic DNA Replication
- DNA polymerase is fixed, and template RNA is threaded through it
Replication at the Ends of Chromosomes
- Telomeres and telomerase are involved
- If telomeres were not replicated by telomerase, chromosomes would shorten after each replication
- Telomerase replicates the ends of chromosomes
- G-overhang
- Contains protein and RNA components
- Extends the telomere after polymerase sees a 3' OH and extends
Replication at the Ends of Chromosomes - Telomerase
- Unclear how the other strand is synthesized
Telomerase Mutation
- If telomerase were mutated and nonfunctional, chromosomes would shorten each generation
DNA polymerase I
- 5' to 3' polymerase and 3' to 5' exonuclease activities
- Primarily used for removing RNA primers and replacing them with DNA nucleotides
- 5' to 3' exonuclease activity is used to remove primers laid down by primase and to replace them with DNA nucleotides
- Takes out RNA nucleotides and puts in DNA nucleotides
DNA polymerase I and DNA Ligase
- 5' to 3' exonuclease activity removes primers and replaces them with DNA nucleotides
- DNA ligase creates a phosphodiester bond without adding another nucleotide to the strand
- All that is left is DNA
Bacterial DNA Replication
- Requires a large number of enzymes and proteins
- Replication fidelity is high (less than one mistake per billion nucleotides)
- Proofreading: DNA polymerase I's 3' to 5' exonuclease activity removes incorrectly paired nucleotides
- Mismatch Repair: corrects errors after replication is completed
- Distinguishes between old and new strands of DNA to determine which base to remove
- Termination occurs when replication forks meet or by a termination protein.
Eukaryotic DNA Replication
- Aut autonomously replicating sequences (ARSs) are 100-120 bps long (origin of replication)
- Origin-recognition complex (ORC) binds to ARSs to initiate replication
- Replication is licensed by the replication licensing factor
- MCM (Minichromosome maintenance) binds DNA and initiates replication as a helicase on all origins
- Eukaryotic DNA polymerase
Genetic Information must be Accurately Copied
- One error per million base pairs leads to 6400 mistakes each time a cell divides
- Replication occurs at high speed in E.coli (1000 nucleotides per second)
DNA Replication Models
- Conservative Replication Model
- Dispersive Replication Model
- Semiconservative Replication
Meselson and Stahl’s Experiment
- Distinguished between isotopes of nitrogen used in nucleotides
- E.coli was grown in 15N media, then transferred to 14N media
- Cultured E.coli were subjected to equilibrium density gradient centrifugation
Meselson and Stahl’s Experiment- Centrifugation
- Heavier 15N will sink to the bottom
- Conservative replication model predicts one heavy and one light band after one round of replication
Modes of Replication
-
Replicons: Units of replication
- Have one origin of replication in bacteria, and many in eukaryotic chromosomes
-
Theta Replication: In circular DNA (E.coli)
- Single origin of replication forms a replication fork, and the replication is bidirectional
-
Rolling-Circle Replication: In viruses and F-factor of E.coli
- Single origin of replication
- The inside of the circle is a template, and is replicated
- The outside of the circle is displaced and replicated
-
Linear Eukaryotic Replication: Eukaryotic cells
- Thousands of origins
- Replicon is around 200,000- 300,000 bp in length
Linear Eukaryotic Replication
- Requires a template strand, raw materials (nucleotides) and enzymes
Synthesis of New DNA
- DNA strands are antiparallel: one strand runs 5' to 3' and the other strand runs 3' to 5'
- DNA polymerases add nucleotides onto the 3' end of the growing strand
- Replication only goes from 5' to 3'
- Continuous and discontinuous replication
Direction of Replication
- Antiparallel nature of DNA strands means one template is exposed in the 5' to 3' direction and the other in the 3' to 5' direction
- Synthesis can happen simultaneously on both strands at the fork
- Continuous replication keeps going
- Discontinuous replication stops and starts
Bacterial DNA Replication
- Initiation proteins: unwind DNA and make a replication bubble (245 bps in the oriC)
- Initiation protein: DnaA in E.coli
- Unwinding:
- Initiator Protein:
- DNA Helicase
- Single-strand-binding proteins (SSBs)
- DNA Gyrase (topoisomerase)
Initiation of Replication in E.coli
- DnaA causes the replication bubble to open
- SSB holds the bubble open
Unwinding of DNA
- DNA helicase unwinds DNA
- Single-strand binding proteins (SSBs) keep the strands separated
- Topoisomerase relieves tension ahead of the replication fork
Elongation: DNA Primer Synthesis
- DNA needs a primer with a 3-OH group to begin
- Primers are usually 10-12 nucleotides long
- DNA primase synthesizes an RNA primer
Elongation: DNA Polymerase III
- DNA polymerase III is the main workhorse of replication
- 5' to 3' polymerase activity allows it to add new nucleotides
- 3' to 5' exonuclease activity allows it to remove nucleotides to correct errors
Removing RNA Primers: DNA Polymerase I
- DNA polymerase I removes RNA primers and replaces them with DNA nucleotides
- DNA ligase connects nicks after the RNA primers are removed
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Description
This quiz explores the critical processes involved in eukaryotic DNA replication, highlighting key differences from bacterial replication. It focuses on the role of histone proteins in nucleosome formation and the significance of telomeres and telomerase in maintaining chromosome integrity. Test your knowledge on these fundamental concepts of molecular biology.
