DNA Replication and Polymerase Quiz

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Questions and Answers

What is required for the synthesis of the leading strand during DNA replication?

Multiple DNA polymerases

A single RNA primer (correct)

A series of RNA primers

No RNA primer

What enzyme is specifically responsible for synthesizing the RNA primer on the lagging strand template?

DNA gyrase

DNA ligase

DNA polymerase III

DNA primase (correct)

Which enzyme is responsible for joining Okazaki fragments during DNA replication?

DNA gyrase

DNA ligase (correct)

DNA polymerase I

DNA helicase

What direction does DNA polymerase III synthesize the leading strand?

5’ to 3’ direction Signup and view all the answers

What happens to the RNA primer once the DNA polymerase I replaces it with DNA nucleotides?

It is digested and removed Signup and view all the answers

How are the Okazaki fragments synthesized on the lagging strand?

In a series of short segments Signup and view all the answers

Which activity of DNA polymerase I is responsible for extending the newly formed DNA strand?

5’ to 3’ polymerase activity Signup and view all the answers

What structure is left between two adjacent Okazaki fragments after RNA primer replacement?

A single-stranded nick Signup and view all the answers

What is the role of DNA ligase in DNA replication?

It joins DNA fragments by forming phosphodiester bonds. Signup and view all the answers

Where does the termination of DNA replication occur?

In the Ter region. Signup and view all the answers

What is the function of the Ter-Tus complex in DNA replication?

To halt one of the replication forks. Signup and view all the answers

How are the Okazaki fragments processed during DNA replication?

They are looped to bring them close to the polymerase. Signup and view all the answers

What is the role of Pol δ during DNA replication?

Synthesis of the lagging strand Signup and view all the answers

What role does Topoisomerase IV play in the termination of DNA replication?

It separates interlinked circular DNA molecules. Signup and view all the answers

Which statement about the replisome is accurate?

It moves as a unit while synthesizing new DNA. Signup and view all the answers

What initiates the synthesis of Okazaki fragments on the lagging strand?

RNA/DNA primers Signup and view all the answers

Which components are key proteins associated with the replisome during DNA replication?

DNA polymerase III and helicase. Signup and view all the answers

What is the function of RNase H in Okazaki fragment processing?

Removes RNA nucleotides Signup and view all the answers

What mechanism allows the lagging-strand polymerase to synthesize Okazaki fragments efficiently?

It repeatedly engages with other proteins at the fork. Signup and view all the answers

Which protein is involved in removing RPA to allow FEN1 to cut off the flap during Okazaki fragment processing?

DNA2 Signup and view all the answers

What is the primary function of PCNA in the elongation phase of DNA replication?

Sliding clamp for DNA polymerase Signup and view all the answers

At which stage of DNA replication is the end replication problem most significant?

Termination Signup and view all the answers

What is the significance of the single-stranded overhang at the 5’ ends of newly synthesized DNA strands?

Cannot be filled by DNA polymerase Signup and view all the answers

Which enzyme is primarily responsible for synthesizing telomeric DNA in eukaryotes?

Telomerase Signup and view all the answers

Study Notes

DNA Replication

DNA replication is the process where DNA makes a copy of itself.
Three models for DNA replication were proposed:
- Semiconservative: Each new DNA molecule is made of one original strand and one new strand.
- Conservative: One new DNA molecule retains both original strands, and one new DNA molecule contains two new strands.
- Dispersive: Original and new DNA segments are interspersed in both new strands.
Meselson and Stahl's experiment provided evidence that the semiconservative model is correct.
- Bacteria were grown in a medium containing a heavy isotope of nitrogen (15N).
- The DNA was extracted and its density was measured.
- The results of successive generations matched the semiconservative model's predictions.

DNA Polymerase

Enzymes that catalyze the polymerization of nucleotide precursors (deoxyribonucleotides)
In 1955, Arthur Kornberg identified these enzymes.
Found in prokaryotes and eukaryotes.
DNA polymerase III is the enzyme involved in replication.
DNA is copied in a 5' to 3' direction on the template strand
Leading strand is synthesized continuously.
Lagging strand is synthesized discontinuously (Okazaki fragments)

Mechanism of DNA Elongation

At the growing end of the DNA chain, DNA polymerase forms a phosphodiester bond between the 3'-OH of the last nucleotide and the 5' phosphate of a dNTP
In each step, polymerase finds the correct dNTP
Nucleotide addition is rapid in prokaryotes ( ~ 850 per second).
High accuracy, low error frequency.

Mechanism of DNA Replication

Initiation is directed by a DNA sequence called the replicator.
The initiation of replication in a circular chromosome has a specific region call oriC
E.coli initiator protein DnaA
E.coli helicase (DnaB) and helicase loader (DnaC) are recruited.
Once the DNA is unwound, a replication bubble forms.
Replication forks move in opposite directions.

Termination of Replication

Termination occurs at a specific region of the DNA termed the Ter region.
Tus proteins (terminus utilization substances) bind to the Ter region.
The Ter-Tus complex halts the replication fork progression.

Replication Bubble

The segment of unwound DNA resulting from the separation of DNA stands during initiation of replication.
The replication forks move in opposite directions away from the origin of replication.

Rolling Circle Replication

Replication that produces linear DNA from a circular template.
A nick is created in one strand of the double helix.
The displaced strand is used as a template to initiate the synthesis of a complementary strand.

DNA Replication in Eukaryotes

Eukaryotes have linear chromosomes & multiple origins of replication
Relatively slower than prokaryotes, due to multiple origins of replication.
The end replication problem: The inability to completely replicate the ends of linear chromosomes.
Telomerase: An enzyme that adds telomeric repeats to the ends of chromosomes, solving the end-replication problem. Telomerase RNA provides a template for synthesis.

Okazaki Fragments

Short DNA fragments made during lagging strand synthesis.
These fragments are later joined together by DNA ligase.

Eukaryotic DNA Replication

Multiple origins of replication are found in eukaryotic chromosomes to speed up the process.
Different DNA polymerases participate.
Elongation uses leading and lagging strands like prokaryotes.
Post-replication processing includes removal of RNA primers and joining of Okazaki fragments by special enzymes.
There are specific mechanisms to cope with the end-replication problem in linear chromosomes.

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Description

Test your understanding of DNA replication processes, including the semiconservative, conservative, and dispersive models. Explore the significance of Meselson and Stahl's experiment, and learn about DNA polymerases and their functions. This quiz covers key concepts relevant for biology students.