DNA Replication Quiz

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Questions and Answers

What type of DNA strand is synthesized continuously towards the replication fork?

Leading strand (correct)

Okazaki strand

Primer strand

Lagging strand

What is the primary reason for the discontinuous synthesis of one of the DNA strands?

The enzyme DNA ligase cannot operate efficiently

RNA primers are too short for continuous synthesis

Lagging strand must wait for more template to be exposed (correct)

DNA polymerase can only add nucleotides to the 5’ end

What are the small segments synthesized on the lagging strand called?

Okazaki fragments (correct)

RNA primers

Polymerase fragments

Leading segments

What enzyme is responsible for joining Okazaki fragments into a continuous strand?

DNA ligase Signup and view all the answers

How is the initiation of each fragment on the lagging strand accomplished?

By RNA polymerase synthesizing a short RNA primer Signup and view all the answers

What term is given to the process of DNA replication where one strand is continuous and the other is not?

Semidiscontinuous replication Signup and view all the answers

Which part of the Okazaki fragments grows toward the previously synthesized fragment?

5’ end Signup and view all the answers

What key role does primase play in DNA replication?

It initiates synthesis of RNA primers Signup and view all the answers

What is a characteristic of the β-globin locus in erythroid cells during S phase?

It replicates earlier than in nonerythroid cells. Signup and view all the answers

What is the core element of an ARS (autonomous replicating sequence)?

A conserved sequence of 11 base pairs. Signup and view all the answers

How does the timing of replication initiation differ between cells with shorter and longer cell cycles?

Shorter cell cycle cells utilize a greater number of sites as origins of replication. Signup and view all the answers

What is the function of the origin recognition complex (ORC) in eukaryotic cells?

To bind proteins required for the initiation of replication at specific origins. Signup and view all the answers

What ensures that each portion of the genome is replicated once during a cell cycle?

Mechanisms that prevent reinitiation of replication at already duplicated sites. Signup and view all the answers

What factors influence the selection of sites for the initiation of replication?

Local epigenetic factors such as nucleosome positions and histone modifications. Signup and view all the answers

Which statement describes the behavior of the ORC protein complex in yeast cells?

It remains associated with the origin throughout the cell cycle. Signup and view all the answers

In vertebrates, how is replication initiation different compared to yeast?

Vertebrate DNA has exactly no initiation sequences. Signup and view all the answers

What is the primary function of DnaB in E. coli?

DNA helicase that unwinds parental duplex Signup and view all the answers

Which eukaryotic protein serves a similar function to DnaC in E. coli?

Cdc6, Cdt1 Signup and view all the answers

What is the role of SSB in E. coli replication?

Maintains DNA in single-stranded state Signup and view all the answers

Which enzyme acts as a clamp loader in eukaryotic DNA replication?

RFC (Replication Factor C) Signup and view all the answers

Which statement is true about eukaryotic polymerases in comparison to bacterial polymerases?

Both types of polymerases have proofreading capabilities. Signup and view all the answers

What is the function of the β clamp in E. coli?

Clamps replicating polymerase to DNA Signup and view all the answers

What primarily influences the transcriptional state of a cell?

The epigenetic state of the cell's chromatin Signup and view all the answers

How do DNA polymerases ensure high fidelity during DNA replication?

By possessing a 3’ → 5’ exonuclease activity Signup and view all the answers

Replication forks are localized at which specific sites within the cell nucleus?

Replication foci Signup and view all the answers

How are DNA methylation patterns transmitted during cell division?

Through the action of DNA methyltransferase DNMT1 Signup and view all the answers

What is one reason that DNA repair is more complex in eukaryotic cells compared to prokaryotic cells?

Eukaryotic DNA is within folded chromatin fibers Signup and view all the answers

Which of the following describes how damaged DNA is often repaired?

By excising damaged sections and using the complementary strand as a template Signup and view all the answers

What role do modifications on old histones play in chromatin inheritance?

They guide the modification of new histones Signup and view all the answers

Which enzyme is responsible for directly repairing damage caused by certain alkylating agents in humans?

Alkyltransferase Signup and view all the answers

What mechanism allows the complementary strand of DNA to aid in repair?

The information contained in one strand for reconstructing its partner Signup and view all the answers

What is the defining characteristic of epigenetic information?

It is independent of DNA sequence Signup and view all the answers

What is one major difference in DNA replication between E.coli and eukaryotic cells?

E.coli replicates DNA faster than eukaryotic cells. Signup and view all the answers

What role does the RNA primer play in DNA synthesis?

It initiates the DNA synthesis process. Signup and view all the answers

Why is the study of replication in eukaryotic cells considered more complex than in bacteria?

Eukaryotic cells possess complex chromosomal structures. Signup and view all the answers

Which experimental system has been important for studying eukaryotic DNA replication?

Xenopus frog egg extracts. Signup and view all the answers

How does the rate of nucleotide incorporation by eukaryotic polymerases compare to that of E.coli?

Eukaryotic polymerases are slower. Signup and view all the answers

What is the approximate time it takes for E.coli to complete its DNA replication?

40 minutes. Signup and view all the answers

What happens to RNA primers during the DNA synthesis process?

They are replaced with DNA. Signup and view all the answers

What common characteristic do archaeal and eukaryotic replication proteins share?

Both types are homologous to one another. Signup and view all the answers

Study Notes

DNA Replication

DNA replication occurs in a semi-discontinuous manner, meaning one strand is replicated continuously (leading strand) and the other discontinuously (lagging strand).
The lagging strand is synthesized in small fragments called Okazaki fragments, about 1000 to 2000 nucleotides long.
Okazaki fragments are joined together by DNA ligase.
DNA synthesis is initiated by a primase enzyme, which creates a short RNA primer initiating the process.
E. coli replicates its DNA in approximately 40 minutes, but a new round can begin before the previous one is completed.

Eukaryotic Replication

Eukaryotic cells have large genomes and complex chromosomal structures, making eukaryotic replication more complex than prokaryotic replication.
Eukaryotic replication is studied using mutant yeast and animal cells, archaeal species, and in vitro systems, including Xenopus frog egg extracts.
Eukaryotic DNA replication initiates at multiple origins, unlike prokaryotic replication.
Replication origins in yeast contain conserved sequences called autonomous replicating sequences (ARSs), which are recognized by the origin recognition complex (ORC).

Replication Control

Each portion of the genome is replicated only once per cell cycle.
The initiation of replication requires the origin to pass through several distinct states.
The ORC protein complex plays a significant role in binding essential proteins required for subsequent steps in replication.
The selection of sites for initiation of replication is governed by local epigenetic factors such as nucleosome positions, histone modifications, DNA methylation, and transcription levels.

Eukaryotic Replication Proteins

Eukaryotic DNA polymerases function similarly to bacterial polymerases, synthesizing DNA strands in the 5' → 3' direction.
Eukaryotic DNA polymerases δ and ɛ are the primary replicating enzymes, synthesizing both the leading strand and Okazaki fragments.
Eukaryotic DNA polymerase α synthesizes short DNA oligonucleotides as part of the RNA-DNA primer.
Eukaryotic replication occurs within localized sites called replication foci.

Epigenetic Inheritance

Epigenetic information that is not encoded within a chromosome's DNA sequence is crucial for cellular functions.
DNA methylation patterns are transmitted through the DNA methyltransferase DNMT1, which uses the parental DNA strand as a template.

DNA Repair

Both prokaryotic and eukaryotic cells possess DNA repair mechanisms involving a range of proteins that detect and repair DNA damage.
DNA damage can be repaired directly or by excising the damaged section, using the complementary strand as a template for reconstruction.
DNA repair in eukaryotes involves chromatin-reshaping machines such as histone-modifying enzymes and nucleosome remodeling complexes.

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Description

Test your knowledge on DNA replication, including the differences between prokaryotic and eukaryotic processes. This quiz covers key concepts such as leading and lagging strands, Okazaki fragments, and the role of enzymes like primase and DNA ligase. Perfect for students studying molecular biology or genetics.