Unit 2: Replication of DNA

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Questions and Answers

What type of DNA replication was proven by the Meselson-Stahl experiment?

Semi-conservative (correct)

Dispersive

Conservative

Non-conservative

Which statement is true about the direction of DNA replication?

Replication occurs in the direction of the 3' end to the 5' end.

Nucleotides are always added at the 3' end. (correct)

Nucleotides are added at the 5' end of the growing strand.

DNA replication occurs in both 5' to 3' and 3' to 5' directions.

What is required for DNA replication to initiate?

A specific enzyme that can initiate without a primer

A free 5'-OH end of a nucleotide

A nucleosome to condense the DNA

A short nucleic acid sequence known as a primer (correct)

How does the replication of the leading strand differ from the lagging strand?

The leading strand is replicated continuously, while the lagging strand is replicated discontinuously. Signup and view all the answers

Which of the following is NOT a type of DNA polymerase found in E. coli?

DNA polymerase VI Signup and view all the answers

What initiates the strand separation during the initiation phase of DNA replication?

DnaA protein Signup and view all the answers

Which type of fragments are formed during the synthesis of the lagging strand?

Okazaki fragments Signup and view all the answers

What role does DnaC protein play in DNA replication?

It loads DnaB helicase on the DNA strands. Signup and view all the answers

How does DNA Polymerase III add nucleotides during elongation?

By catalyzing dNTP addition on the 3’-OH end of primers Signup and view all the answers

What is the function of DNA ligase in DNA replication?

To form phosphodiester bonds between DNA fragments Signup and view all the answers

Which ions help in the addition of nucleotides by DNA Polymerase III?

Mg+2 and Zn+2 Signup and view all the answers

What leads to the termination of DNA replication?

Encountering the Ter sequence Signup and view all the answers

Which protein follows DNA Polymerase III to proofread and remove RNA primers?

DNA polymerase I Signup and view all the answers

What is the main enzyme responsible for replication in eukaryotic cells?

DNA polymerase 𝝳 Signup and view all the answers

Which phase of the cell cycle does eukaryotic DNA replication occur?

S phase Signup and view all the answers

What characteristic is unique to eukaryotic DNA replication compared to prokaryotic replication?

Multiple origins of replication Signup and view all the answers

What is the role of DNA polymerase 𝜶 in eukaryotic replication?

Synthesizing primers Signup and view all the answers

Which DNA polymerase is primarily involved in DNA repair in eukaryotic cells?

DNA polymerase 𝜄 Signup and view all the answers

What is the primary significance of DNA replication in cellular processes?

It ensures that new daughter cells contain a complete set of DNA. Signup and view all the answers

Which mode of DNA replication involves each parental strand acting as a template to produce two new strands?

Semi-Conservative Replication Signup and view all the answers

What did the Meselson-Stahl experiment demonstrate about DNA replication?

DNA replication is semi-conservative in nature. Signup and view all the answers

After one generation in the 14N medium, what was the observed density of DNA in the Meselson-Stahl experiment?

Intermediate density, between 14N and 15N. Signup and view all the answers

What were the results after two generations in the 14N medium, according to the results from the Meselson-Stahl experiment?

Two bands were observed, one for light DNA and one for hybrid DNA. Signup and view all the answers

What is the main characteristic of conservative replication?

Both parental strands remain intact and are used as templates. Signup and view all the answers

In dispersive replication, what is unique about the daughter DNAs after the replication process?

They have equal portions of parental and newly synthesized DNA interspersed. Signup and view all the answers

What experimental method was used to analyze the DNA density in the Meselson-Stahl experiment?

Cesium chloride density gradient centrifugation Signup and view all the answers

What is the main function of DNA Polymerase I?

DNA replication, recombination and repair Signup and view all the answers

Which DNA polymerase is primarily responsible for DNA repair during SOS response?

DNA Polymerase IV Signup and view all the answers

What type of structure does the sliding clamp of DNA Polymerase III consist of?

Ring-shaped structure Signup and view all the answers

Which DNA polymerase has the highest processivity rate?

DNA Polymerase III Signup and view all the answers

What subunits comprise the catalytic core of DNA Polymerase III?

α, ε, and θ subunits Signup and view all the answers

Which is NOT a feature of DNA Polymerase II?

Gap filling activity Signup and view all the answers

Which of the following properties is associated with DNA Polymerase V?

Translesion synthesis during SOS response Signup and view all the answers

Which protein is NOT part of the clamp loader complex in DNA Polymerase III?

ε Signup and view all the answers

Study Notes

DNA Replication Overview

DNA replication produces two identical DNA replicas from one original molecule, ensuring each daughter cell has complete DNA after cell division.
Critical for genetic continuity across generations.

Modes of DNA Replication

Conservative Replication: Original strands re-associate, yielding one all-old and one all-new DNA double helix.
Semi-Conservative Replication: Each parental strand serves as a template for new strands; results in two DNA molecules with one strand old and one strand new.
Dispersive Replication: Daughter DNA comprises interspersed segments of both parental and newly synthesized DNA.

Meselson-Stahl Experiment

Conducted in 1958, demonstrating semi-conservative replication using E. coli with heavy nitrogen isotopes.
After transition from 15N to 14N medium, DNA density showed intermediate results, confirming semi-conservative replication with hybrid DNA bands.

Key Features of DNA Replication

Semi-Conservative Process: Each new DNA molecule contains one original and one newly synthesized strand.
Bi-Directional: Origin of replication (ori) allows replication to proceed in both directions, forming a replication bubble.
Requires a Primer: Short nucleic acid sequence is needed for DNA polymerases, which cannot initiate synthesis de novo.
Directionality: DNA strands are synthesized from 5' to 3', adding nucleotides at the 3' end.
Semi-Discontinuous Process: Leading strand is synthesized continuously, while the lagging strand is synthesized in short segments called Okazaki fragments.

Role of DNA Polymerases

Enzymes that catalyze DNA synthesis by forming phosphodiester bonds among nucleotides.
E. coli DNA Polymerases:
- DNA Polymerase I: Main role in DNA replication, recombination, and repair; has 5' to 3' polymerase and exonuclease activity.
- DNA Polymerase II: Primarily involved in DNA repair.
- DNA Polymerase III: Major enzyme for replication; involved in leading and lagging strand synthesis with high processivity.

Process of DNA Replication

Initiation:
- Begins at the origin of replication (OriC), which includes specific 9-mer and 13-mer sequences.
- Initiator protein DnaA binds to OriC, facilitating strand separation.
- DnaB (helicase) unwinds DNA using ATP, while single-stranded binding proteins prevent reannealing.
- DnaG (primase) synthesizes short RNA primers for DNA polymerases to start synthesis.
Elongation:
- DNA Polymerase III adds nucleotides in 5' to 3' direction on both leading and lagging strands.
- Leading strands synthesized continuously; lagging strands consist of Okazaki fragments.
- DNA Polymerase I replaces RNA primers with DNA, sealing gaps with DNA ligase.
Termination:
- Occurs when replication forks reach the designated Ter region on DNA.
- Parent DNA is copied semi-conservatively, producing two identical daughter DNA molecules.

Eukaryotic DNA Polymerases

Eukaryotic cells have multiple types of DNA polymerases, primarily functioning in nuclear replication.
Key Eukaryotic DNA Polymerases:
- DNA Polymerase δ: Major enzyme replicating eukaryotic DNA with proofreading capability.
- DNA Polymerase α: Synthesizes primers and has primase activity.
- DNA Polymerase γ: Responsible for mitochondrial DNA replication.
- DNA Polymerase ε: Involved in leading strand synthesis.

Comparison of Prokaryotic and Eukaryotic DNA Replication

Prokaryotic:
- Occurs in the cytoplasm.
- Fast replication speed.
- Single origin of replication.
Eukaryotic:
- Takes place in the nucleus.
- Slower replication process.
- Multiple origins of replication.

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Description

Explore the fascinating process of DNA replication in this quiz. Understand how DNA molecules replicate to ensure genetic information is accurately passed to daughter cells. Learn about the different modes of DNA replication, including conservative, semi-conservative, and dispersive methods.