DNA Replication Mechanisms

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Questions and Answers

What is the function of single-stranded binding proteins during DNA replication?

They relieve tension in the DNA helix.

They synthesize RNA primers.

They prevent the reformation of hydrogen bonds. (correct)

They remove RNA primers.

How does DNA polymerase III primarily contribute to DNA replication?

By ligating fragments of DNA together.

By removing damaged sections of DNA.

By synthesizing RNA primers.

By adding nucleotides to the RNA primer. (correct)

Which enzyme is responsible for relieving the tension that develops as the DNA helix unwinds?

Gyrase (correct)

Primase

DNA polymerase I

Ligase

What describes the direction of DNA replication in terms of nucleotide addition?

Replication occurs in a 5'-3' direction only. Signup and view all the answers

What role does the sliding clamp play in DNA polymerase III?

It increases the enzyme's processivity. Signup and view all the answers

Which of the following accurately describes the synthesis of the lagging strand?

It is synthesized discontinuously in short fragments. Signup and view all the answers

Which component of the replisome helps to provide the initial hydroxyl group required for DNA synthesis?

Primase Signup and view all the answers

What is the primary role of DNA polymerases II, IV, and V?

To assist in the repair of damaged DNA. Signup and view all the answers

What distinguishes eukaryotic DNA replication from prokaryotic DNA replication regarding the origin of replication?

Eukaryotes have multiple origins of replication. Signup and view all the answers

During DNA replication in eukaryotes, what happens to histones?

Histones double in count during replication. Signup and view all the answers

Which statement correctly describes the structure of nucleosomes?

Nucleosomes are made of DNA wound around eight histone proteins. Signup and view all the answers

What is the role of DNA polymerase alpha in eukaryotic DNA synthesis?

It synthesizes the RNA primer and adds a short chain of nucleotides. Signup and view all the answers

Which of the following accurately describes Okazaki fragments in eukaryotes?

Okazaki fragments are involved in the synthesis of the lagging strand. Signup and view all the answers

What is the primary function of telomerase in relation to telomeres?

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

What is a significant difference in the termination process of eukaryotic and prokaryotic DNA replication?

Eukaryotic termination involves the replication of chromosome ends known as telomeres. Signup and view all the answers

What requirement is essential for both prokaryotic and eukaryotic DNA synthesis?

A template and primer are needed. Signup and view all the answers

Which component of telomerase serves as a template for DNA synthesis?

TERC Signup and view all the answers

During homologous recombination, what is the role of endonucleases?

To nick the DNA strands at specific positions. Signup and view all the answers

How does the rate of DNA synthesis compare between prokaryotes and eukaryotes?

Prokaryotic DNA synthesis occurs at a much faster rate than eukaryotic synthesis. Signup and view all the answers

What process follows the strand displacement in homologous recombination to extend the heteroduplex DNA?

Branch migration. Signup and view all the answers

Which protein is considered crucial for the process of homologous recombination?

RecA Signup and view all the answers

What is the outcome of DNA ligation in the recombination process?

Formation of hybrid heteroduplex DNA molecules. Signup and view all the answers

Why do most somatic cells experience telomere shortening over time?

They lack the TERT gene that encodes telomerase. Signup and view all the answers

In the context of DNA synthesis, what does the lagging strand require to successfully elongate?

Nucleotides complementary to the strand. Signup and view all the answers

Study Notes

DNA Polymerase Functions

DNA polymerase I removes RNA primers and fills gaps using 5’-3’ exonuclease activity, allowing for proofreading.
DNA polymerases II, IV, and V are involved in repairing damage caused by external forces like UV light.

DNA Polymerase III Holoenzyme

Composed of two core enzymes, a sliding clamp loader, and a sliding clamp to enhance processivity.
Major enzyme complex for prokaryotic DNA replication, adding nucleotides to RNA primers and synthesizing leading and lagging DNA strands.
Enzymes and proteins at the replication fork form a structure known as the replisome.

Mechanism of DNA Synthesis

DNA replication is bidirectional but occurs biochemically in one direction (5' to 3').
Single-stranded binding proteins prevent reformation of hydrogen bonds.
Gyrase alleviates tension from unwinding DNA.
Primase provides RNA fragments necessary for DNA polymerase III to start polymerization.
Leading strand synthesis is continuous; lagging strand synthesis involves Okazaki fragments and is discontinuous.
Lagging strand gaps are filled and ligated post-replication.

Eukaryotic DNA Synthesis

Requires deoxyribonucleoside triphosphates (dNTPs), template, and primer.
More complex due to increased DNA volume and linear chromosomes, with DNA dissociating from histones before replication.
Synthesis of DNA and production of histones occurs simultaneously, doubling histone count during replication.

Comparison: Prokaryotic vs. Eukaryotic Replication

Prokaryotes have a single origin of replication; eukaryotes have multiple.
Prokaryotes expand from a single replication loop; eukaryotes have multiple loops for increased efficiency.
Prokaryotic replication ends at a single termination site; eukaryotic involves merging two replication forks and telomere replication.

Eukaryotic DNA Polymerases

Pol α initiates and synthesizes the RNA primer, adds 10-20 nucleotides, and is replaced by Pol δ and Pol ε for further synthesis.
Pol δ synthesizes the lagging strand; Pol ε synthesizes the leading strand.
Pol γ is responsible for mitochondrial DNA replication.

Telomeres and Aging

Linear chromosome ends, known as telomeres, shorten with repeated cell divisions in somatic cells lacking telomerase.
Telomeres contain repetitive G-rich sequences and do not code for genes.
TERT gene encodes telomerase reverse transcriptase crucial for telomere maintenance.
TERC component serves as a guide for enzyme attachment and as a template for DNA synthesis.

DNA Recombination

Occurs through reciprocal exchange of homologous chromosomes involving several steps:
- Endonuclease nicks DNA strands.
- Strand displacement pairs loose ends with complementary sequences.
- Ligation forms hybrid heteroduplex DNA.
Cross-bridged configurations move down chromosomes via branch migration, resulting in longer heteroduplex regions.
Formation of the chi-form/Holliday structure precedes additional endonuclease nicking and final ligation, completing recombinant duplex formation.
Key protein involved is RecA in homologous recombination.

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Description

This quiz focuses on the various DNA polymerases and their roles in DNA replication and repair mechanisms. It delves into the specific functions of DNA polymerase III, as well as the proofreading capabilities of DNA enzymes. Understand the significance of these processes in prokaryotic cells.