Lecture 4: DNA Replication

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Questions and Answers

What is the minimum number of polypeptides required for DNA polymerase III functional activity?

One

Two

Five

Three (correct)

Who discovered DNA polymerase I in 1958?

Arthur Kornberg (correct)

Francis Crick

James Watson

Rosalind Franklin

What is the role of DNA ligase in DNA replication?

Forming phosphodiester bonds (correct)

Unwinding of parental DNA

Synthesizing RNA primers

Initiating DNA synthesis

What is the approximate length of Okazaki fragments in prokaryotic cells?

2000 nucleotides Signup and view all the answers

Which DNA polymerase is involved in the replication of mitochondrial DNA?

Gamma Signup and view all the answers

What is the primary function of DNA polymerase delta?

Completing replication on leading and lagging strands Signup and view all the answers

Which DNA polymerase is responsible for initiating nuclear DNA synthesis?

Alpha Signup and view all the answers

What is the primary function of DNA polymerase beta?

Repairing DNA damage Signup and view all the answers

What is the key characteristic of semi-conservative replication?

Each of the progeny DNA molecules conserves half of the original DNA molecule. Signup and view all the answers

What is the main problem with conservative and dispersive replication?

They do not immediately suggest a mechanism for copying the information in the sequence of bases. Signup and view all the answers

What is the function of CsCl2 equilibrium density gradient centrifugation in the Meselson and Stahl experiment?

To separate DNA molecules based on their density. Signup and view all the answers

What is the difference between 14N and 15N ammonium salts?

The isotope of nitrogen. Signup and view all the answers

What is the significance of the Watson and Crick DNA model?

It suggested how genetic information might be replicated. Signup and view all the answers

What is the characteristic of DNA from E. coli cells grown with 15N ammonium salts?

It has a higher density than DNA grown in 'normal' (14N) ammonium salts. Signup and view all the answers

What is the purpose of the Meselson and Stahl experiment?

To determine the mechanism of DNA replication. Signup and view all the answers

What is the characteristic of prokaryotic organisms?

They lack a true membrane-bound nucleus and cellular organelles. Signup and view all the answers

Which DNA polymerase appears to take part in nuclear replication of both the leading and the lagging strands?

DNA polymerase (epsilon) Signup and view all the answers

What type of replication occurs in eukaryotes?

Semi-conservative replication Signup and view all the answers

What is the function of replication licensing factor (RLF)?

To bind to the DNA next to each origin before each replication cycle Signup and view all the answers

How many replication origins are estimated to be in a dividing human somatic cell?

10,000-100,000 Signup and view all the answers

What is the term for the bulges where the DNA is in the process of division?

Replication bubbles Signup and view all the answers

How does DNA replication occur in eukaryotes?

Bi-directional Signup and view all the answers

What is the function of other DNA polymerases?

To allow replication to bypass damaged DNA or play a role in DNA repair Signup and view all the answers

How are the new strands synthesized in eukaryotic DNA replication?

One strand is synthesized continuously and the other in fragments Signup and view all the answers

What determines the migration position of DNA in centrifugation?

Density of DNA Signup and view all the answers

What was the result of switching E.coli to 14N media after growing them in 15N salts?

A single band of intermediate density was observed Signup and view all the answers

What is the mode of DNA replication supported by the results of Meselson and Stahl's experiment?

Semi-conservative Signup and view all the answers

What is the function of DNA polymerase in DNA replication?

Deoxynucleotide polymerization Signup and view all the answers

What is the role of RNA primers in DNA replication?

To initiate DNA synthesis Signup and view all the answers

What is the function of helicase in DNA replication?

To unwind DNA Signup and view all the answers

What is the name of the complex that constitutes helicase and primase?

Primosome Signup and view all the answers

What is the name of the protein that melts duplex DNA in the oriC region?

dnaA Signup and view all the answers

What is the purpose of DNA replication?

To create an identical copy of the DNA for each descendant cell Signup and view all the answers

What is the base pairing rule in DNA replication?

A pairs with T and G pairs with C Signup and view all the answers

What happens to the two DNA strands in the first stage of replication?

They are separated Signup and view all the answers

What is the replication fork?

The zone of DNA where the strands are separated Signup and view all the answers

What is the result of DNA replication?

Two double-stranded DNA molecules with identical sequences Signup and view all the answers

How many nucleotides per second are synthesized in E. coli?

1,000 nucleotides per second Signup and view all the answers

What is the role of the replisome?

To synthesize new DNA strands Signup and view all the answers

Study Notes

DNA Replication

DNA replication is a two-stage process that occurs at the replication fork
The first stage separates the two DNA strands of the parental DNA molecule
The second stage builds two new strands using each of the two original strands as templates
Base pairing occurs between A and T, and between G and C
Each of the separated parental strands of DNA serves as a template strand for the synthesis of a new complementary strand
Synthesis of both new strands of DNA occurs at the replication fork that moves along the parental molecule

Semi-Conservative Replication

There are three possible strategies for replication of the double helix: semi-conservative, conservative, and dispersive
Semi-conservative replication is the most satisfactory mechanism, as it allows for copying the information in the sequence of bases
In semi-conservative replication, each of the progeny conserves half of the original DNA molecule
One of the two “daughter” double helices consists entirely of original DNA strands, while the other helix consists of two newly synthesized strands

Meselson and Stahl Experiment

In 1958, Meselson and Stahl performed an experiment to determine the mode of replication
They grew E. coli in 15N ammonium salts, which resulted in DNA with a higher density than normal DNA
When they switched the media to 14N salts, the DNA density changed
After one round of replication, a single band of intermediate density was observed
After a second round of replication, two bands were present in approximately equimolar amounts
The results were consistent with a semi-conservative mode of replication for DNA

Mechanism of DNA Replication

The process involves deoxyribonucleotide precursors synthesis, deoxynucleotide polymerization, and enzymes and proteins such as DNA polymerase, primase, and ligase
RNA primers are also involved in the process
The steps in E. coli DNA synthesis include:
- dnaA protein melts duplex in oriC region
- dnaB (helicase) and dnaC protein bind to replication fork
- Single-strand binding protein (ssb protein) binds to separated strands of DNA
- Primase complexes with helicase and creates RNA primers
- DNA pol III holoenzyme extends the RNA primer on the leading strand

Prokaryotic and Eukaryotic Replication

Prokaryotic replication occurs in bacteria, while eukaryotic replication occurs in eukaryotic cells such as plants and animals
Eukaryotic chromosomes are longer and have multiple replication origins scattered along each chromosome
Replication is bi-directional, with a pair of replication forks starting at each origin of replication
Eukaryotic DNA replication involves multiple DNA polymerases, including alpha, delta, gamma, and epsilon

Replication Licensing Factor (RLF)

RLF is a protein complex that binds to the DNA next to each origin before each replication cycle
RLF is displaced during replication and ensures that each origin initiates once and once only during each replication cycle

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Description

This quiz covers the process of DNA replication, including the two-stage process that occurs at the replication fork, and the separation of the two DNA strands of the parental DNA molecule.