DNA Replication: Mechanisms Overview

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Questions and Answers

What is the primary consequence of errors occurring during DNA replication?

Changes in genetic information may arise. (correct)

The DNA will replicate slower.

The cell cannot divide successfully.

All future replications will be error-free.

How many base pairs are present in a single-celled human zygote?

3.2 billion

4.6 million

640 million

6.4 billion (correct)

What rate does Escherichia coli replicate its DNA?

1000 nucleotides per second (correct)

1000 nucleotides per minute

100 nucleotides per second

10,000 nucleotides per day

What is the significance of the complementary nature of DNA strands during replication?

Each strand serves as a template for synthesis of a new strand. Signup and view all the answers

What was a major finding of Watson and Crick regarding DNA structure?

Base pairing specificity is essential for accurate replication. Signup and view all the answers

What would happen if DNA replication did not occur accurately?

The ability of cells to function properly could be impaired. Signup and view all the answers

How many errors might occur if there is a low error rate of one per million base pairs in a single human cell division?

6400 errors Signup and view all the answers

What challenge do multicellular organisms face regarding genetic information during cell division?

Preventing changes in genetic information. Signup and view all the answers

Which proteins facilitate the reassembly of nucleosomes during DNA replication?

Histone chaperones Signup and view all the answers

What is the composition of the H2A-H2B dimer?

One H2A and one H2B histone Signup and view all the answers

Where does most DNA replication occur within a eukaryotic nucleus?

In replication factories Signup and view all the answers

What mistakenly depicts the role of DNA polymerases in replication?

They slide along the DNA strand. Signup and view all the answers

What role does chromatin-assembly factor 1 (CAF-1) play during nucleosome formation?

It assists in nucleosome assembly. Signup and view all the answers

What is the consequence of RNA primers being removed during eukaryotic DNA replication?

It leads to incomplete DNA strands. Signup and view all the answers

Which histone component is transferred randomly to one of the new DNA molecules during replication?

Old H3-H4 tetramer Signup and view all the answers

What forms the foundation for new nucleosomes after DNA replication?

Old H3-H4 tetramers Signup and view all the answers

What is homologous recombination primarily responsible for during meiosis?

The exchange of genetic information. Signup and view all the answers

What structure is formed during one of the pathways of homologous recombination?

Holliday junction. Signup and view all the answers

What happens to genetic information during homologous recombination?

Genetic information is shuffled into new combinations. Signup and view all the answers

Where does homologous recombination generally occur within the cell cycle?

During prophase I of meiosis. Signup and view all the answers

What role does recombination play in genetic mapping?

It provides information on linkage relations among genes. Signup and view all the answers

What term describes DNA that is formed from nucleotide strands from different sources?

Heteroduplex DNA. Signup and view all the answers

Which process is essential for some types of DNA repair in cells?

Homologous recombination. Signup and view all the answers

What initiates the process of homologous recombination in one of its pathways?

Single-strand break in each of two DNA molecules. Signup and view all the answers

What is the role of telomerase in relation to telomeres?

It adds DNA nucleotides to the 3' end of the G-rich strand. Signup and view all the answers

In which type of cells is telomerase activity typically present?

Single-celled eukaryotes Signup and view all the answers

What happens to somatic cells that have little to no telomerase activity?

Their chromosomes become unstable as telomeres shorten. Signup and view all the answers

How does telomerase extend the 3' G-rich overhang of the chromosome?

Through a ribonucleoprotein complex that provides a nucleotide template. Signup and view all the answers

What may happen if telomeres shorten beyond a critical point?

The chromosomes may undergo rearrangements and become degraded. Signup and view all the answers

What is the primary consequence observed in genetically engineered mice lacking functional telomerase?

Significant premature aging symptoms. Signup and view all the answers

What role does the RNA component of telomerase play?

It provides a template for synthesizing DNA copies of telomere repeats. Signup and view all the answers

Why is the synthesis of the complementary C-rich strand considered unclear?

Its synthesis may be coupled with conventional replication mechanisms. Signup and view all the answers

What is the primary issue identified as the end-replication problem?

Loss of DNA nucleotides at the end of linear chromosomes during replication. Signup and view all the answers

How much DNA is typically not replicated at the end of human chromosomes?

70 to 100 nucleotides Signup and view all the answers

What feature do telomeres possess that helps prevent chromosome shortening?

Multiple copies of a short repeated sequence. Signup and view all the answers

Which of the following is true regarding the position of the terminal primer in human chromosomes?

It is situated about 70 to 100 nucleotides from the chromosome end. Signup and view all the answers

What is the role of telomerase in the context of chromosome replication?

It adds nucleotides to the ends of chromosomes, counteracting shortening. Signup and view all the answers

In which type of cells do chromosomes not shorten due to the end-replication problem?

Germ cells Signup and view all the answers

What happens to linear chromosomal DNA when replicating in a way that exposes the end-replication problem?

It progressively shortens with each cell division. Signup and view all the answers

What is the repeated sequence present in human telomeres?

TTAGGG Signup and view all the answers

What is the point where the nucleotide strands pass from one DNA molecule to the other called?

Holliday junction Signup and view all the answers

What type of recombinant is produced when cleavage occurs in the horizontal plane?

Noncrossover recombinant Signup and view all the answers

Which of the following processes occurs during recombination?

Branch migration Signup and view all the answers

In which model does the removal of nucleotides at the ends of broken strands initiate recombination?

Double-strand-break model Signup and view all the answers

What determines whether crossover or noncrossover molecules are produced during recombination?

The plane of cleavage Signup and view all the answers

What role do enzymes play in the process of recombination?

Unwinding, cleaving, and joining DNA strands Signup and view all the answers

Which organism has been extensively studied for the molecular mechanism of recombination?

Escherichia coli Signup and view all the answers

What is the result of strand invasion and joining during the recombination process?

Production of heteroduplex DNAs Signup and view all the answers

What is the primary mode of replication found in circular DNA such as that in E.coli?

Theta replication Signup and view all the answers

Which structure forms as double-stranded DNA unwinds during replication?

Replication bubble Signup and view all the answers

In which mode of replication do replication forks proceed outward in both directions?

Bidirectional replication Signup and view all the answers

What term describes a segment of DNA that is undergoing replication?

Replicon Signup and view all the answers

Which feature distinguishes bacterial chromosomes from eukaryotic chromosomes in terms of replication?

Bacterial chromosomes have a single origin of replication. Signup and view all the answers

What is generated by the unwinding of double-stranded DNA at the origin of replication?

Replication bubbles Signup and view all the answers

What characteristic of semiconservative replication did Meselson and Stahl's results specifically confirm?

It produces both light and heavy DNA. Signup and view all the answers

What is the function of a replication fork during DNA replication?

Separates nucleotide strands from each other Signup and view all the answers

What is the primary function of DNA polymerase α during DNA replication?

Synthesize RNA primers and initial DNA Signup and view all the answers

Which DNA polymerases are primarily responsible for replicating the leading strand in eukaryotic cells?

DNA polymerase δ and ɛ Signup and view all the answers

How do high-fidelity DNA polymerases differ from specialized translesion DNA polymerases?

Translesion polymerases can copy templates with abnormal bases Signup and view all the answers

What consequence occurs when high-fidelity DNA polymerases encounter distorted DNA templates?

They stall and cannot proceed Signup and view all the answers

Why does chemotherapy make many patients sick in addition to targeting cancer cells?

It inhibits the replication of normal, noncancerous cells Signup and view all the answers

Which property of DNA polymerase δ and DNA polymerase ɛ contributes to their ability to replicate DNA with high fidelity?

Active sites that snugly accommodate normal nucleotides Signup and view all the answers

What is a characteristic of translesion DNA polymerases that distinguishes them from high-fidelity polymerases?

Ability to accommodate abnormal bases Signup and view all the answers

What is the function of histone chaperones during DNA replication?

To facilitate the transfer of old histones and assist in nucleosome assembly Signup and view all the answers

Which components make up the H2A-H2B dimer?

One H2A and one H2B histone Signup and view all the answers

What evidence suggests about the movement of DNA polymerases during replication?

They are fixed in place while the DNA template moves through them. Signup and view all the answers

How are new nucleosomes formed after DNA replication is complete?

A combination of old and newly synthesized histones are used. Signup and view all the answers

What characterizes replication factories in the eukaryotic nucleus?

They are stationary sites where multiple DNA replication occurs. Signup and view all the answers

What is the role of chromatin-assembly factor 1 (CAF-1) in nucleosome formation?

It facilitates the assembly of nucleosomes by adding histones. Signup and view all the answers

Why do eukaryotic chromosomes face a unique challenge during replication?

They are linear and have ends that must be managed. Signup and view all the answers

What is the primary issue associated with RNA primers during eukaryotic DNA replication?

They need to be removed and replaced with DNA nucleotides eventually. Signup and view all the answers

What technique did Meselson and Stahl use to distinguish between DNA densities?

Equilibrium density gradient centrifugation Signup and view all the answers

What is the expected result of DNA replication in a medium containing only ^(15)N over multiple generations?

One band at the expected position of ^(15)N Signup and view all the answers

After switching the bacteria to a medium with ^(14)N, what was observed after one round of replication?

A band at an intermediate position Signup and view all the answers

What does the semiconservative model of DNA replication predict after two rounds of replication in ^(14)N?

One band at an intermediate density and one at ^(14)N density Signup and view all the answers

What does the presence of two bands of equal intensity after the second generation indicate?

Both semiconservative and dispersive models match the data Signup and view all the answers

What distinguishes the conservative replication model from the results observed by Meselson and Stahl?

Predicts two bands of different densities after two generations Signup and view all the answers

In Meselson and Stahl's experiment, what was the sole nitrogen source used to grow the initial E.coli culture?

^(15)N Signup and view all the answers

What was the outcome when only one generation of E.coli was allowed to replicate in ^(14)N after previous growth in ^(15)N?

A single band at an intermediate position Signup and view all the answers

What is the primary role of translesion DNA polymerases during DNA replication?

To bypass DNA lesions and continue replication Signup and view all the answers

Which of the following best describes the process of nucleosome assembly after DNA replication?

A mixture of old and new histones forms new nucleosomes Signup and view all the answers

What method was used to determine the composition of histones after DNA replication?

Density gradient centrifugation Signup and view all the answers

What consequence does the activity of translesion DNA polymerases have on DNA replication?

They increase the mutation rate by allowing errors to persist Signup and view all the answers

How does the chromatin structure change during the DNA replication process?

It is disrupted and slowly reassembles afterwards Signup and view all the answers

What is the significance of the continuous band formed by histone octamers in density gradient centrifugation?

It shows a mixing of old and new assembled histones Signup and view all the answers

Which statement about DNA polymerases during replication is accurate?

High-fidelity polymerases resume replication after translesion polymerases Signup and view all the answers

What occurs immediately prior to the reassembly of nucleosomes after DNA replication?

Original nucleosomes are disrupted on parental DNA Signup and view all the answers

What occurs at the end of a linear chromosome that creates a gap after primer removal?

The terminal primer cannot be replaced by DNA nucleotides. Signup and view all the answers

How do telomeres prevent chromosomes from shortening during cell division?

By employing telomerase to replicate the ends. Signup and view all the answers

What is the significance of the sequence TTAGGG in human chromosomes?

It is a telomeric repeat essential for chromosome stability. Signup and view all the answers

Why do human chromosomes shorten at a much faster rate than expected?

The terminal primer is located further from the chromosome end. Signup and view all the answers

What is the term used to describe the issue related to chromosome shortening in eukaryotes?

End-replication problem. Signup and view all the answers

In what type of cells are telomerase typically active?

Germ cells and early embryonic cells. Signup and view all the answers

What distinguishes the ends of chromosomes in single-celled eukaryotes such as yeast from those in humans?

Yeast chromosomes can replicate their ends completely. Signup and view all the answers

What happens to the ends of chromosomes during somatic cell division?

The chromosome shortens by about 70 to 100 nucleotides. Signup and view all the answers

Study Notes

DNA Replication: An Overview

DNA replication is the process of copying a DNA molecule
It's a crucial process for cell division, ensuring each new cell receives a complete copy of the genetic material
Errors in replication can lead to mutations

Mechanisms of DNA Replication

Semiconservative Replication: Replication results in two DNA molecules, each with one old and one new strand.
Theta Replication: Involves a circular DNA molecule with a replication bubble forming a theta shape. Replication proceeds bidirectionally from the origin site.
Rolling-Circle Replication: Starts with a break in one strand of a circular DNA molecule. The broken strand is extended and used as template. The displaced strand also replicates to form multiple copies.
Linear Replication: In eukaryotes with linear chromosomes, DNA replicates at multiple origins along the chromosome, creating multiple replication bubbles. Each bubble is replicated bidirectionally.

Replication in Bacteria (Specific Examples)

Origin of Replication (oriC): Specific region on bacterial DNA where replication begins.
Initiator proteins (DnaA): Bind to oriC to initiate DNA unwinding.
Helicase: Opens the double helix by breaking hydrogen bonds.
Single-stranded binding proteins (SSBs): Stabilize the unwound DNA strands.
Topoisomerase (DNA gyrase): Relieves the torsional strain (supercoiling) ahead of the replication fork.
Primase: Synthesizes short RNA primers which provide a 3'-OH group for DNA polymerase.
DNA Polymerase III: Main enzyme for synthesizing new DNA strands in a 5'→ 3' direction. Utilizing the sliding clamp enhances process efficiency and processivity.
DNA Polymerase I: Removes RNA primers and replaces them with DNA.
DNA Ligase: Joins the Okazaki fragments (segments of DNA on the lagging strand) together.

Replication in Eukaryotes (Specific Examples)

Multiple Origins of Replication: Eukaryotic chromosomes have many origins of replication which allows replication to proceed faster. Replication occurs in both directions from each origin. Replication is regulated to occur only once per cell cycle utilizing replication licensing factors.
Telomeres: The ends of linear eukaryotic chromosomes which contain repetitive sequences, such as TTAGGG in humans. Telomeres prevent the loss of genetic information during replication. Telomerase extends telomeres, preventing shortening.
Telomerase: An enzyme that replicates telomeres. Its presence prevents chromosome shortening with each cell division.

DNA Polymerases

There are multiple DNA polymerases (e.g., I and III in bacteria, α, δ, ε in eukaryotes) in each cell.
DNA polymerase III is the major enzyme in bacteria for synthesis of new DNA strands, providing high processivity and accuracy.

Fidelity of Replication

The process is highly accurate which is critical for avoiding mutations.
Three mechanisms help maintain accuracy: nucleotide selection, proofreading (3'-5' exonuclease activity), and mismatch repair.

Replication and the Cell Cycle

Eukaryotic replication is precisely coordinated with the cell cycle, primarily S-Phase.
Licensing factors ensure replication occurs only once per cell cycle

Recombination

Recombination is the exchange of genetic material between DNA molecules.
Homologous recombination (e.g. crossing over in meiosis) is crucial for genetic diversity.
It also plays a critical role in DNA repair.
Recombination requires precise breaking and rejoining of the DNA strands.

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Description

Explore the fundamental mechanisms of DNA replication in this quiz. Understand the importance of semiconservative, theta, rolling-circle, and linear replication processes. Learn how these mechanisms ensure genetic material is accurately copied during cell division.