PTH241 Lecture 5: DNA Replication

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Questions and Answers

What is the role of topoisomerases I?

They are involved in the synthesis of DNA.

They bind DNA to single-strand binding proteins.

They make a transient break in two DNA strands.

They make a transient break in one DNA strand. (correct)

What is the function of single-strand binding proteins (SSBPs) during DNA replication?

They unwind the DNA double helix.

They synthesize RNA primers.

They proofread DNA during synthesis.

They stabilize single strands of DNA. (correct)

Which protein complex is responsible for the initial unwinding of DNA at the origin of replication?

Single-strand binding proteins.

DNA polymerase III.

DnaB and DnaC. (correct)

Topoisomerase II.

What is the role of primase in DNA replication?

It synthesizes RNA primers. Signup and view all the answers

What occurs during the synthesis of DNA at the replication fork?

Both strands of parental DNA act as templates for synthesis. Signup and view all the answers

What does DNA polymerase I do in the context of DNA replication?

It degrades RNA primers and replaces them with DNA. Signup and view all the answers

How does DNA polymerase III contribute to DNA replication?

It synthesizes both leading and lagging strands by adding nucleotides to 3' ends. Signup and view all the answers

Which of the following statements about helicases is true?

They bind to the origin of replication to unwind the DNA double helix. Signup and view all the answers

What proteins are involved in forming the Pre-priming complex?

DnaA protein, SSB proteins, DNA helicases Signup and view all the answers

In which direction can DNA polymerase III synthesize a new strand?

5' to 3' Signup and view all the answers

What characterizes the leading strand during DNA replication?

Synthesized in a continuous manner Signup and view all the answers

What is the role of the RNA primer in DNA replication?

To initiate the synthesis of new DNA strands Signup and view all the answers

What are Okazaki fragments?

Short DNA segments formed on the lagging strand Signup and view all the answers

How is the synthesis of the lagging strand characterized?

It occurs discontinuously Signup and view all the answers

What happens to the RNA primers after replication is completed?

They are removed and gaps are filled with DNA Signup and view all the answers

Which of the following correctly describes the replication fork?

It represents the region where DNA strands are unwound Signup and view all the answers

Which protein assists in separating the two DNA strands during replication?

SSB proteins Signup and view all the answers

What is the main function of DNA helicase in DNA replication?

To unwind the DNA double helix Signup and view all the answers

What is true about the direction of the leading and lagging strands?

The leading strand is synthesized toward the fork while the lagging strand is synthesized away Signup and view all the answers

What role does DnaA protein play in DNA replication?

It forms the Pre-priming complex Signup and view all the answers

What is the primary function of RnaseH in DNA replication?

To remove RNA primers Signup and view all the answers

Which enzyme is responsible for the elongation of the 3'-end of telomeres in eukaryotic DNA?

Telomerase Signup and view all the answers

Why do eukaryotic cells have multiple origins of replication?

To speed up the replication process Signup and view all the answers

What is a critical function of topoisomerases during DNA replication?

To remove positive supercoils ahead of the replication fork Signup and view all the answers

If a mammalian genome replicates at the same rate as bacteria, how long would it take to replicate?

150 hours Signup and view all the answers

What occurs after the removal of RNA primers in the lagging strand replication?

The gap cannot be filled in with DNA Signup and view all the answers

Which enzyme is NOT involved in the joining of adjacent DNA segments?

RnaseH Signup and view all the answers

What is the effect of telomerase on the chromosomes of eukaryotic cells?

It prevents shortening of telomeres Signup and view all the answers

What is the flow of genetic information in the Central Dogma of Molecular Biology?

DNA to RNA to protein Signup and view all the answers

What type of replication is described in the context of DNA synthesis?

Semiconservative replication Signup and view all the answers

Which of the following correctly identifies a difference between eukaryotic and prokaryotic DNA replication?

Eukaryotic DNA replication occurs in the nucleus, while prokaryotic replication occurs in the cytoplasm. Signup and view all the answers

What is the primary function of telomerase enzyme during DNA replication?

To extend the telomeres of chromosomes Signup and view all the answers

Which enzyme is NOT typically involved in DNA replication?

RNA polymerase Signup and view all the answers

What is the role of mRNA in the process of transcription?

To convey genetic information from DNA to ribosomes Signup and view all the answers

Which statement about DNA replication is FALSE?

Replication occurs at the same rate in all organisms. Signup and view all the answers

What do tRNAs do in the process of translation?

Carry amino acids to the ribosome Signup and view all the answers

What is the primary function of telomeres?

To protect chromosome ends from nucleases Signup and view all the answers

Which repetitive sequence is found in human telomeres?

5'-TTAGGG-3' Signup and view all the answers

What happens to telomeres as cells undergo division?

They get slightly shorter with each division Signup and view all the answers

What role does telomerase play in cells that do not age?

It replaces lost ends of telomeres Signup and view all the answers

What type of enzyme is telomerase?

Reverse transcriptase Signup and view all the answers

What is the function of DNA polymerase δ during DNA replication in eukaryotes?

Synthesis of the lagging strand Signup and view all the answers

What does telomerase use as a template for synthesizing DNA?

A section of the RNA molecule it carries Signup and view all the answers

What is the purpose of single strand binding proteins in DNA replication?

To prevent DNA strands from re-annealing Signup and view all the answers

How much does telomerase elongate the parental strand during synthesis?

About 100 nucleotides Signup and view all the answers

How long are Okazaki fragments in eukaryotic DNA replication?

100-200 nucleotides Signup and view all the answers

Which enzyme completes the synthesis of the telomere after elongation by telomerase?

DNA polymerase Signup and view all the answers

Which enzyme is responsible for the unwinding of DNA strands during replication?

DNA helicase Signup and view all the answers

What role does DNA topoisomerase play in DNA replication?

It removes supercoils from the DNA helix Signup and view all the answers

Which DNA polymerase is specifically associated with DNA repair?

DNA polymerase β Signup and view all the answers

What is the primary function of the DNA polymerase α-primase complex?

Synthesis of RNA primers and short DNA stretches Signup and view all the answers

Which enzyme is implicated in joining DNA fragments together after replication?

DNA ligase Signup and view all the answers

Study Notes

DNA Replication Lecture Notes

Course: PTH241, Lecture 5
Topic: DNA Replication
Instructor: Hanan H. Fouad

Intended Learning Outcomes

Define the flow of genetic information
Understand basic facts of DNA replication
Identify enzymes and protein factors involved in DNA replication
Explain differences between eukaryotic and prokaryotic replication
Discuss the function of the telomerase enzyme

Central Dogma of Molecular Biology

Describes the flow of information from DNA to RNA to protein
Generally applicable to all organisms, except some viruses that store genetic information in RNA.

DNA Synthesis (Replication)

The major function of DNA replication is to provide genetic code for daughter cells from parent cells.
Each parental DNA strand serves as a template for the complementary DNA strands
Replication produces two daughter DNA molecules, each with one original (conserved) strand and one newly synthesized strand (semi-conservative replication).

Replication in Prokaryotes (e.g., E. coli)

Replication begins at a unique origin
Proceeds in opposite directions simultaneously from the origin (replication fork).

Enzymes of DNA Replication

DNA Polymerases: catalyze polynucleotide chain formation, synthesizing the new DNA strand in the 5' to 3' direction; DNA polymerase needs RNA primer.
DNA Ligase: joins segments of DNA
DNA Helicase: unwinds the DNA double helix (removes the helix)

DNA Topoisomerases

Removes positive supercoils
Topoisomerase I makes a transient break in one DNA strand
Topoisomerase II makes a transient break in two DNA strands

Steps of Prokaryotic Replication

Origin of replication (ori C): binding sites for DNA-binding proteins (dnaA).
Binding of dnaA protein opens and unwinds the DNA double helix.

Formation of Two Replication forks

A complex of dnaB and dnaC also binds to oriC, opening the DNA duplex.
Single-strand binding proteins (SSBP) bind single DNA strands, stabilizing them.
DNA helicase and SSBP formation of replication fork.

Synthesis of Both DNA Strands

At the replication fork, both parent DNA strands serve as templates.
RNA primer is formed by primase (a DNA-dependent RNA polymerase) to initiate DNA synthesis.
DNA polymerase III elongates the primers.
DNA polymerase III synthesizes both leading and lagging strands.

Proteins Involved in the Replication Fork

DnaA protein & DNA Helicase: recognize origin of replication, unwind double helix
Single stranded DNA-binding proteins (SSBP): keep DNA strands separate; protects DNA from nucleases.

DNA Polymerase I, II, III

DNA polymerase I: degrades RNA primers; replaces with DNA
DNA polymerase II: proofreading; repairs replication defects
DNA polymerase III: synthesizes leading and lagging strands.

Pre-priming complex

Composed of: DnaA protein, SSB proteins, and DNA helicases.
Responsible for initiation and maintaining separation of DNA strands

Replication in Eukaryotes

Process is more complex due to bound histones.
DNA replication requires multiple origins.
The time needed to replicate a mammalian genome is roughly 9 hours. Rate is fast.
In eukaryotes, Okazaki fragments are smaller (100-200 nucleotides) than in prokaryotes.

Telomerase

Protects chromosome ends (telomeres) from shortening during replication.
Replicates the 3' end of the lagging strand.
Contains its own RNA molecule as a template for DNA synthesis.
Maintains telomere length.

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Description

This quiz focuses on DNA replication, covering essential concepts such as the flow of genetic information, key enzymes involved, and differences between eukaryotic and prokaryotic replication. Students will also explore the role of telomerase in the replication process. Perfect for those studying molecular biology or genetics.