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?

<p>It synthesizes RNA primers. (C)</p> Signup and view all the answers

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

<p>Both strands of parental DNA act as templates for synthesis. (B)</p> Signup and view all the answers

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

<p>It degrades RNA primers and replaces them with DNA. (A)</p> Signup and view all the answers

How does DNA polymerase III contribute to DNA replication?

<p>It synthesizes both leading and lagging strands by adding nucleotides to 3' ends. (A)</p> Signup and view all the answers

Which of the following statements about helicases is true?

<p>They bind to the origin of replication to unwind the DNA double helix. (A)</p> Signup and view all the answers

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

<p>DnaA protein, SSB proteins, DNA helicases (A)</p> Signup and view all the answers

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

<p>5' to 3' (B)</p> Signup and view all the answers

What characterizes the leading strand during DNA replication?

<p>Synthesized in a continuous manner (A)</p> Signup and view all the answers

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

<p>To initiate the synthesis of new DNA strands (A)</p> Signup and view all the answers

What are Okazaki fragments?

<p>Short DNA segments formed on the lagging strand (C)</p> Signup and view all the answers

How is the synthesis of the lagging strand characterized?

<p>It occurs discontinuously (B)</p> Signup and view all the answers

What happens to the RNA primers after replication is completed?

<p>They are removed and gaps are filled with DNA (C)</p> Signup and view all the answers

Which of the following correctly describes the replication fork?

<p>It represents the region where DNA strands are unwound (B)</p> Signup and view all the answers

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

<p>SSB proteins (A)</p> Signup and view all the answers

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

<p>To unwind the DNA double helix (B)</p> Signup and view all the answers

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

<p>The leading strand is synthesized toward the fork while the lagging strand is synthesized away (A)</p> Signup and view all the answers

What role does DnaA protein play in DNA replication?

<p>It forms the Pre-priming complex (A)</p> Signup and view all the answers

What is the primary function of RnaseH in DNA replication?

<p>To remove RNA primers (C)</p> Signup and view all the answers

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

<p>Telomerase (B)</p> Signup and view all the answers

Why do eukaryotic cells have multiple origins of replication?

<p>To speed up the replication process (A)</p> Signup and view all the answers

What is a critical function of topoisomerases during DNA replication?

<p>To remove positive supercoils ahead of the replication fork (C)</p> Signup and view all the answers

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

<p>150 hours (A)</p> Signup and view all the answers

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

<p>The gap cannot be filled in with DNA (B)</p> Signup and view all the answers

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

<p>RnaseH (B)</p> Signup and view all the answers

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

<p>It prevents shortening of telomeres (D)</p> Signup and view all the answers

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

<p>DNA to RNA to protein (B)</p> Signup and view all the answers

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

<p>Semiconservative replication (B)</p> Signup and view all the answers

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

<p>Eukaryotic DNA replication occurs in the nucleus, while prokaryotic replication occurs in the cytoplasm. (C)</p> Signup and view all the answers

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

<p>To extend the telomeres of chromosomes (C)</p> Signup and view all the answers

Which enzyme is NOT typically involved in DNA replication?

<p>RNA polymerase (D)</p> Signup and view all the answers

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

<p>To convey genetic information from DNA to ribosomes (B)</p> Signup and view all the answers

Which statement about DNA replication is FALSE?

<p>Replication occurs at the same rate in all organisms. (D)</p> Signup and view all the answers

What do tRNAs do in the process of translation?

<p>Carry amino acids to the ribosome (B)</p> Signup and view all the answers

What is the primary function of telomeres?

<p>To protect chromosome ends from nucleases (C)</p> Signup and view all the answers

Which repetitive sequence is found in human telomeres?

<p>5'-TTAGGG-3' (D)</p> Signup and view all the answers

What happens to telomeres as cells undergo division?

<p>They get slightly shorter with each division (A)</p> Signup and view all the answers

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

<p>It replaces lost ends of telomeres (D)</p> Signup and view all the answers

What type of enzyme is telomerase?

<p>Reverse transcriptase (A)</p> Signup and view all the answers

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

<p>Synthesis of the lagging strand (B)</p> Signup and view all the answers

What does telomerase use as a template for synthesizing DNA?

<p>A section of the RNA molecule it carries (A)</p> Signup and view all the answers

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

<p>To prevent DNA strands from re-annealing (C)</p> Signup and view all the answers

How much does telomerase elongate the parental strand during synthesis?

<p>About 100 nucleotides (C)</p> Signup and view all the answers

How long are Okazaki fragments in eukaryotic DNA replication?

<p>100-200 nucleotides (A)</p> Signup and view all the answers

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

<p>DNA polymerase (C)</p> Signup and view all the answers

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

<p>DNA helicase (C)</p> Signup and view all the answers

What role does DNA topoisomerase play in DNA replication?

<p>It removes supercoils from the DNA helix (D)</p> Signup and view all the answers

Which DNA polymerase is specifically associated with DNA repair?

<p>DNA polymerase β (B)</p> Signup and view all the answers

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

<p>Synthesis of RNA primers and short DNA stretches (B)</p> Signup and view all the answers

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

<p>DNA ligase (B)</p> Signup and view all the answers

Flashcards

Central Dogma

The flow of genetic information from DNA to RNA to protein.

DNA Replication

The process of creating a duplicate copy of a DNA molecule.

Semiconservative Replication

Method of DNA replication where each new double helix has one old and one new strand.

Transcription

The process of creating an RNA molecule from a DNA template.

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Translation

The process of using the RNA sequence to create a protein.

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Genetic Information

The sequence of nucleotides in DNA that holds the instructions for building and maintaining an organism.

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DNA

Deoxyribonucleic Acid. The molecule that carries the genetic instructions for all living organisms.

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Nucleotide

The building block of DNA, consisting of a sugar, a phosphate, and a base.

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Topoisomerase I function

Topoisomerase I makes a temporary break in one DNA strand to relieve DNA supercoiling during replication.

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Topoisomerase II function

Topoisomerase II makes a temporary break in two DNA strands to relieve DNA supercoiling during replication.

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Origin of Replication (oriC)

The specific DNA sequence where DNA replication begins in prokaryotes.

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DNA Helicase (e.g., dnaB)

An enzyme that unwinds the DNA double helix during replication by breaking hydrogen bonds.

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Single-Strand Binding Proteins (SSBPs)

Proteins that bind to separated DNA strands to prevent them from re-annealing.

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DNA Polymerase III

The enzyme primarily responsible for synthesizing new DNA strands during replication.

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RNA Primer

Short RNA segment that initiates DNA synthesis by providing a 3'-OH group for DNA polymerase.

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Replication Fork

The Y-shaped region where DNA replication occurs.

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RnaseH function

Removes RNA primers from the newly synthesized DNA strand during replication.

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DNA ligase function

Connects the newly synthesized DNA fragments (Okazaki fragments) together on the lagging strand.

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Telomerase function

Adds repetitive DNA sequences (telomeres) to the ends of chromosomes to prevent shortening during replication.

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Helicases function

Unwind the DNA double helix by breaking hydrogen bonds between the bases.

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Endonucleases function

Cut DNA strands within the molecule.

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Exonucleases function

Remove nucleotides from the ends of DNA strands.

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SSBP function

Stabilize the separated DNA strands during replication by preventing them from rebinding.

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Lagging Strand

The DNA strand synthesized discontinuously during replication, in short segments called Okazaki fragments, due to its 3' to 5' direction.

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Okazaki Fragments

Short segments of DNA synthesized on the lagging strand during replication, later joined together by DNA ligase.

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DNA Ligase

An enzyme that joins the Okazaki fragments together on the lagging strand, creating a continuous DNA strand.

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DNA Polymerases in Eukaryotes

Several DNA polymerases work together in eukaryotes; each has a specific role in the process.

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DNA Polymerase α-primase

A complex that synthesizes RNA primers and short DNA stretches on the lagging strand.

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DNA Topoisomerases

Enzymes that relieve the tension caused by DNA unwinding during replication, preventing the DNA from becoming tangled.

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Telomere

A protective cap at the end of a chromosome, composed of repetitive DNA sequences and proteins. It prevents degradation and helps maintain chromosome integrity.

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Telomere Shortening

The gradual loss of telomere sequences with each cell division, contributing to cellular aging and senescence.

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Telomerase

An enzyme responsible for maintaining telomere length by adding repetitive DNA sequences to the ends of chromosomes. It is active in germ cells and cancer cells.

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Reverse Transcriptase

An enzyme that synthesizes DNA using an RNA template. Telomerase is a special kind of reverse transcriptase.

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Telomerase RNA Template

A specific RNA molecule within telomerase that serves as a template to add DNA repeats to the telomere.

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Lagging Strand Telomere Synthesis

The process of completing the telomere sequence on the lagging strand after the parental strand is elongated by telomerase.

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Cellular Aging and Death

Telomere shortening with each cell division leads to a loss of genetic material and contributes to cellular senescence, ultimately causing death.

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Cancer Cells and Telomerase

Cancer cells often have high telomerase activity, which allows them to maintain telomere length and proliferate indefinitely.

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Pre-priming Complex

A group of proteins (DnaA, SSB, and DNA Helicases) that initiate and maintain the separation of DNA strands during replication.

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DnaA Protein

A protein that binds to the origin of replication (oriC) on DNA, initiating the unwinding process.

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SSB Proteins

Single-stranded DNA binding proteins that stabilize the separated DNA strands, preventing them from re-annealing.

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Primase

An enzyme that synthesizes short RNA primers, which are necessary to initiate DNA synthesis.

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Continuous Synthesis

The synthesis of a new DNA strand in one continuous direction, without interruptions.

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Discontinuous Synthesis

The synthesis of a new DNA strand in short fragments, with gaps between them.

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What is the role of SSB proteins in DNA replication?

SSB proteins bind to single-stranded DNA, preventing them from re-annealing, and stabilizing the unwound strands during replication.

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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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PTH241 DNA Replication - Fall 2024 - Galala University PDF

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.

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