DNA Replication Processes and Mechanisms

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Why is the presence of multiple replication bubbles beneficial in eukaryotic DNA replication, compared to the process in bacteria?

The larger size and complexity of eukaryotic genomes necessitate multiple replication origins to ensure timely and efficient duplication. (correct)
Eukaryotic DNA is inherently more stable and requires less precise replication, allowing for multiple origins without compromising fidelity.
Eukaryotic cells lack the necessary enzymes to efficiently replicate DNA from a single origin.
Unlike bacteria, eukaryotic DNA polymerase has a lower processivity, requiring frequent initiation events at multiple origins.

How does topoisomerase facilitate DNA replication?

By relieving the torsional strain ahead of the replication fork, preventing supercoiling. (correct)
By directly separating the two DNA strands at the origin of replication, initiating the process.
By joining the single-strand binding proteins to stabilize the unwound DNA strands.
By preventing the formation of replication forks.

What would be the most likely immediate consequence if single-strand binding proteins were non-functional during DNA replication?

Helicase would stall at the replication fork due to increased DNA tension.
Topoisomerase activity would increase, leading to excessive DNA supercoiling.
DNA replication would proceed normally but at a slower rate.
The separated DNA strands would re-anneal, preventing access for DNA polymerase. (correct)

The origin of replication is characterized by what feature?

A specific sequence of nucleotides where proteins bind to initiate DNA strand separation. (A) Signup and view all the answers

If a cell were deficient in helicase, what would be the most likely consequence during DNA replication?

Inhibition of the unwinding of the double helix at the replication fork. (B) Signup and view all the answers

If Meselson and Stahl had observed that after the first generation in the lighter medium, all DNA molecules were of the same density as the heavy isotope DNA, and after the second generation, half were heavy and half were light, what mode of replication would that support?

Conservative replication, where the original DNA strands reassociate after serving as a template. (C) Signup and view all the answers

What is the most accurate comparison between the roles of primase and DNA polymerase in DNA replication?

Primase synthesizes short RNA sequences to initiate replication, while DNA polymerase extends these sequences with DNA nucleotides. (A) Signup and view all the answers

Suppose a bacterial cell is cultured in a medium containing only N-15 for many generations. It is then transferred to a medium containing only N-14. After two generations in the N-14 medium, what proportion of the DNA molecules will contain only N-14?

50% (D) Signup and view all the answers

Imagine a hypothetical scenario where primase is non-functional in a cell. What would be the most likely direct consequence of this deficiency during DNA replication?

DNA polymerase would be unable to initiate replication, leading to incomplete synthesis of new DNA strands. (A) Signup and view all the answers

If a mutation occurred that inhibits the activity of primase, but replication still occurs, what is the most likely alternative mechanism that has compensated for the loss of primase function?

A different enzyme is now synthesizing a DNA primer instead of an RNA primer. (C) Signup and view all the answers

If a mutation occurred that disabled primase activity in a cell, what would be the most likely consequence during DNA replication?

DNA polymerase would stall because it cannot add nucleotides without a primer. (C) Signup and view all the answers

During DNA replication, which statement accurately describes the role and directionality of DNA polymerase?

It removes RNA primers and replaces them with DNA, moving in the 5' to 3' direction. (B) Signup and view all the answers

How does the structure of dATP differ from ATP, and why is this difference crucial for DNA synthesis?

dATP contains deoxyribose, while ATP contains ribose; the absence of a hydroxyl group on the 2' carbon in deoxyribose allows for stable DNA structure. (B) Signup and view all the answers

During DNA synthesis, a researcher observes that a particular nucleotide is being added to the growing strand. What chemical process is directly involved in the addition of this nucleotide to the DNA strand?

Dehydration, which removes a water molecule to form a phosphodiester bond between the new nucleotide and the existing strand. (A) Signup and view all the answers

Imagine a cell where DNA replication is occurring, but there's a shortage of deoxyribonucleoside triphosphates (dNTPs). Which of the following outcomes is most likely?

A slowdown or halting of DNA replication due to the unavailability of building blocks for the new strand. (D) Signup and view all the answers

During DNA replication, what is the primary role of pyrophosphate (PPi) release and subsequent breakdown into inorganic phosphate molecules?

To drive the polymerization reaction by releasing energy. (D) Signup and view all the answers

Why does the synthesis of the lagging strand involve the creation of Okazaki fragments?

Because DNA polymerase can only synthesize DNA in the 5' to 3' direction, necessitating discontinuous synthesis away from the replication fork. (A) Signup and view all the answers

In the context of DNA replication, what is the functional significance of the different primer requirements between the leading and lagging strands?

The leading strand, synthesized continuously, requires only one initial primer, while the lagging strand needs a new primer for each Okazaki fragment. (D) Signup and view all the answers

Consider a mutation that inactivates the enzyme responsible for breaking down pyrophosphate (PPi) during DNA replication. What is the most likely direct consequence of this mutation?

Inhibition of the energy supply needed for DNA polymerization (A) Signup and view all the answers

How would the introduction of a modified nucleotide that inhibits the primase activity most directly affect DNA replication?

Okazaki fragment initiation on the lagging strand would be prevented causing replication to halt. (A) Signup and view all the answers

If DNA polymerase III synthesizes an Okazaki fragment and DNA polymerase I subsequently replaces RNA nucleotides with DNA nucleotides, what challenge does DNA ligase primarily address?

Sealing the nicks between the sugar-phosphate backbones of adjacent Okazaki fragments. (A) Signup and view all the answers

During DNA replication, what immediate action does DNA polymerase undertake when it encounters an incorrectly paired nucleotide?

Temporarily stalls replication and repositions to excise and replace the incorrect nucleotide before continuing synthesis. (B) Signup and view all the answers

What distinguishes nucleotide excision repair from other DNA repair mechanisms?

It uses an undamaged strand as a template to replace a removed segment. (D) Signup and view all the answers

How do telomeres contribute to maintaining genomic stability in eukaryotic cells?

By preventing activation of DNA damage monitoring systems at chromosome ends. (C) Signup and view all the answers

Why is DNA ligase essential during DNA replication, particularly on the lagging strand?

It joins Okazaki fragments by catalyzing the formation of phosphodiester bonds to create a continuous strand. (D) Signup and view all the answers

If a cell's mismatch repair system is compromised, what is the most likely outcome?

An elevated mutation rate because incorrectly incorporated bases are not corrected. (B) Signup and view all the answers

What enzymatic activity is directly responsible for excising damaged DNA segments during nucleotide excision repair?

Nuclease (D) Signup and view all the answers

Consider a scenario where DNA polymerase III incorporates an incorrect nucleotide during replication. What is the immediate next step in ensuring the integrity of the newly synthesized DNA strand?

DNA polymerase I proofreads and corrects the error by excising the mismatched nucleotide and replacing it with the correct one. (B) Signup and view all the answers

What is the primary function of the repeating nucleotide sequences within telomeres?

To protect chromosome ends from degradation and fusion. (C) Signup and view all the answers

After a nuclease removes a segment of damaged DNA, which enzyme is directly responsible for adding new nucleotides to fill the gap?

DNA polymerase (D) Signup and view all the answers

What critical function would be compromised in germ cells if telomeres were unable to be maintained?

The integrity and completeness of genetic information passed to offspring would be at risk. (D) Signup and view all the answers

How does the activity of telomerase differ between somatic cells and germ cells, and what is the significance of this difference?

Telomerase is inactive in somatic cells, potentially contributing to aging, but active in germ cells to maintain telomere length during reproduction. (C) Signup and view all the answers

What direct enzymatic activity does telomerase possess that allows it to lengthen telomeres?

Telomerase acts as a reverse transcriptase, using an RNA template to extend the DNA sequence of telomeres. (C) Signup and view all the answers

Assuming a mutation disabled the RNA component of telomerase, what would be the most likely consequence?

Telomeres would progressively shorten with each cell division, potentially leading to cell senescence or apoptosis. (C) Signup and view all the answers

How do telomeric DNA sequences, composed of repetitive nucleotide sequences, protect against the degradation of genes near the ends of chromosomes?

By acting as a buffer zone that is shortened during replication instead of coding DNA. (C) Signup and view all the answers

S phase

The phase in interphase where DNA replication occurs, taking a few hours.

Origins of replication

Specific sequences of nucleotides where DNA replication begins.