DNA Replication Quiz

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Questions and Answers

Which statement correctly describes the fidelity of DNA replication?

It must possess a very high degree of fidelity. (correct)

It depends on the nutrient availability in the cell.

It is moderate and allows for frequent errors.

It is not crucial for cell survival.

During which phase of the cell cycle does DNA replication occur?

S phase (correct)

G2 phase

G1 phase

M phase

Which of the following characteristics is NOT true about the process of DNA replication?

It can occur multiple times during one cell cycle. (correct)

It involves the whole genome.

It requires a primer for initiation.

It is semiconservative.

Which of the following processes is NOT involved in the mechanics of DNA replication?

Elongation of protein chains Signup and view all the answers

What is the direction of DNA synthesis during replication?

5' to 3' Signup and view all the answers

What is the role of DNA polymerase in E. coli during replication?

To catalyze the replication of DNA Signup and view all the answers

Which statement is true about the nature of DNA replication?

It occurs simultaneously in both strands. Signup and view all the answers

Which of the following enzymes are NOT DNA polymerases identified in E. coli?

DNA polymerase-IV Signup and view all the answers

What is the primary function of primase during DNA replication?

Builds RNA primers that are complementary to DNA templates. Signup and view all the answers

Which statement accurately describes the leading strand during DNA replication?

It is synthesized continuously in the 5' to 3' direction. Signup and view all the answers

Which of the following best characterizes the lagging strand during replication?

It requires short segments called Okazaki fragments for synthesis. Signup and view all the answers

What role does DNA polymerase III play in the synthesis of the leading strand?

It synthesizes DNA utilizing the free 3' OH group from an RNA primer. Signup and view all the answers

Where is the lagging strand located relative to the leading strand at the replication fork?

It is located on the opposite side of the replication fork. Signup and view all the answers

What is the approximate length of the RNA primers synthesized by primase?

Approximately 10 nucleotides long. Signup and view all the answers

What prevents DNA polymerase III from synthesizing the lagging strand continuously?

The antiparallel nature of DNA strands. Signup and view all the answers

What are Okazaki fragments?

Short segments of DNA synthesized on the lagging strand. Signup and view all the answers

What role do single stranded binding proteins (SSB) play during DNA replication?

They prevent the unwound strands from re-winding together. Signup and view all the answers

Which enzyme is mainly responsible for the elongation of both leading and lagging strands during DNA replication?

DNA polymerase Signup and view all the answers

In which direction do DNA polymerases synthesize new DNA strands?

5′→3′ direction Signup and view all the answers

What initial protein binds to the origin of replication to start the DNA unwinding process?

DnaA protein Signup and view all the answers

What type of topoisomerase cuts both strands of the DNA double helix?

Type II topoisomerase Signup and view all the answers

Why do DNA replication enzymes encounter positive supercoils ahead of the replication fork?

Due to the unwinding of DNA creating tension. Signup and view all the answers

Which of the following statements about DNA polymerases is false?

They can add nucleotides in the 3′→5′ direction. Signup and view all the answers

What is the consequence of having multiple units of DnaA protein at the origin of replication?

Enhanced helicase activation and DNA unwinding Signup and view all the answers

What is the primary role of DNA polymerase I during DNA replication?

Join DNA fragments together Signup and view all the answers

During replication, what distinguishes the leading strand from the lagging strand?

Leading strand synthesis occurs in a 5' to 3' direction Signup and view all the answers

What role does DNA polymerase I play during DNA replication?

It proofreads the DNA and repairs mismatches. Signup and view all the answers

What type of bond does DNA ligase create between deoxyribonucleotides?

Phosphodiester bonds Signup and view all the answers

Which enzyme is responsible for synthesizing the bulk of the E.coli genome?

DNA polymerase III Signup and view all the answers

Which activity of DNA polymerase III allows it to correct errors during DNA synthesis?

Its 3' to 5' exonuclease activity Signup and view all the answers

Okazaki fragments are formed during the synthesis of which strand?

Lagging strand Signup and view all the answers

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

They stabilize single-stranded DNA. Signup and view all the answers

Which of the following eukaryotic DNA polymerases is responsible for mitochondrial DNA replication?

Pol-γ Signup and view all the answers

What is the function of RNA primers in DNA replication?

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

How does DNA polymerase I remove RNA primers during replication?

Through 5′→3′ exonuclease activity. Signup and view all the answers

What role does DNA polymerase III play in alleviating supercoiling during DNA replication?

By assisting helicase in unwinding DNA Signup and view all the answers

What is the consequence of a malfunctioning DNA polymerase III during synthesis?

Higher likelihood of incorrect nucleotide incorporation Signup and view all the answers

Which accessory protein is primarily responsible for alleviating torsional stress during DNA replication?

Topoisomerase Signup and view all the answers

In what manner does DNA polymerase proofread newly synthesized DNA?

By utilizing 3′→5′ exonuclease activity. Signup and view all the answers

What is the primary function of DNA ligase in DNA replication?

To join Okazaki fragments on the lagging strand. Signup and view all the answers

What is the primary purpose of DNA repair mechanisms?

To maintain genomic integrity and prevent the propagation of mutations Signup and view all the answers

Which of the following is NOT a mechanism of DNA repair?

Exonuclease trim repair (ETR) Signup and view all the answers

How does methylation play a role in mismatch repair?

Methylation helps to identify the correct strand by its degree. Signup and view all the answers

What type of damage occurs as a result of UV light exposure?

Covalent joining of adjacent pyrimidines, forming dimers Signup and view all the answers

What role does DNA ligase play in DNA repair mechanisms?

It fills in gaps left by removal of damaged nucleotides. Signup and view all the answers

Which statement accurately describes the process of base excision repair?

It involves the recognition and excision of damaged single bases. Signup and view all the answers

What is the first step in most DNA repair mechanisms?

Recognition of the damage on the DNA Signup and view all the answers

Which of the following accurately describes hemimethylation in DNA repair?

Only the parental strand is methylated immediately after synthesis. Signup and view all the answers

Study Notes

DNA Replication Overview

DNA replication is the process of creating two identical DNA molecules from a single original DNA molecule.
This is crucial for cell division, ensuring each daughter cell receives a complete set of genetic instructions.
Cells continually divide (e.g., stem cells) or divide a specific number of times until death.
During cell division, everything within the cell must be duplicated for the survival of the resulting daughter cells.
DNA replication is the synthesis of a new DNA strand from the existing template DNA, creating an identical copy.
DNA replication must be highly accurate
The process is complex, involving multiple enzymatic activities.
Replication occurs during the S phase of the cell cycle.
It starts at specific sites in DNA (origins of replication).
It involves several enzymes and proteins.
Replication occurs once during a cell cycle and involves the entire genome.
Replication is template-dependent, guided by base pairing.
Replication requires a primer for initiation.
Replication is semiconservative (each new DNA molecule contains one original strand and one new strand.)
Replication proceeds in a 5' to 3' direction.
Replication occurs bidirectionally and simultaneously in both strands.
DNA replication is semi-discontinuous.

Central Dogma of Molecular Biology

The flow of genetic information in a biological system is often described as the central dogma.
The central dogma is a statement that describes the flow of information from DNA to RNA to protein.
DNA replicates to create more DNA.
DNA is transcribed into RNA.
RNA is translated into protein.

DNA Replication Steps

Identification of origin of replication
Unwinding of double-stranded DNA
Formation of replication bubbles
Establishment of replication fork(s)
Initiation of DNA synthesis
Elongation of DNA
Termination
Reconstitution of chromatin structure

Replication Proteins

Processivity accessory proteins
Helicase: unwinds the DNA double helix
Single-strand binding proteins: stabilize the separated DNA strands.
Primase: synthesizes short RNA primer sequences
Topoisomerases: relieve torsional stress during unwinding
DNA polymerase (pol) I, II, and III: synthesize complementary DNA strands; pol I also involved in primer removal and gap filling
DNA ligase: seals the gaps between DNA fragments.

DNA Polymerase I

It's the most common replicating enzyme in E. coli
Removes RNA primers from the lagging strand, essential for DNA synthesis.
It is involved in proofreading, repairing damaged or mismatched DNA.
The polymerase has 5'→ 3' polymerase as well as 3'→ 5' exonuclease activity.
5'→3' polymerase activity: replacing RNA primer with DNA
3'→5' exonuclease activity: proofreading the synthesized new chain

DNA Polymerase II

It is involved in proofreading and repairing damaged DNA.

DNA Polymerase III

Responsible for bulk replication of the E. coli genome.
Much more active than pol I but less abundant than it.
Its main role is in replicating DNA.

Eukaryotic DNA Polymerases

Five distinct eukaryotic DNA polymerases (alpha, beta, gamma, delta, epsilon) have been identified.
Each is specialized for specific functions in replication – subcellular localization as well as their replicative activities.
Pol δ and ε are equivalent to E. coli Pol III
Pol α is equivalent to E. coli Pol I
Pol γ replicates mitochondrial DNA, and Pol β performs DNA repair.

DNA Replication Direction

Synthesis of new DNA strands occurs in the 5' to 3' direction, antiparallel to the template strand.

Leading and Lagging Strands

Leading strand: synthesized continuously in the same direction as the replication fork's movement.
Lagging strand: synthesized discontinuously in fragments (Okazaki fragments) in the opposite direction. Okazaki fragments are joined by DNA ligase creating a continuous strand.

Okazaki Fragments

Short segments of DNA formed on the lagging strand during DNA replication.
Short stretches of RNA are incorporated into the strand and extended using DNA polymerase.
They are later removed and replaced by DNA, then joined by DNA ligase.

Replication Termination

Leading strand closes in on lagging strand
Ligase completes new strand
Daughter strands paired with original strands resulting in semi-conservative replication
Various proteins work together along the replication fork.

DNA Repair

DNA is constantly subjected to environmental insults which can cause alterations or removal of nucleotide bases.
Repair is critical for maintaining genomic integrity and preventing mutations.
Repair systems involve:
Recognition of the damage on the strand, removal/excision of lesion.
Gap filling, using sister strand as template for DNA repair
Ligation.
Excision repair can be into nucleotide excision and base excision.
Methyl-directed mismatch repair, involves methylation for discrimination steps.
Repair of damage due to UV light (pyrimidine dimers) involves several steps to repair the damage
Non-homologous end joining (NHEJ) alters the original DNA sequence during repair and is used to repair double strand breaks when the cells have not yet duplicated their DNA.
Homologous recombination is a more challenging repair pathway to accomplish but restores the original DNA sequence. It typically occurs after DNA duplication

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Description

Test your knowledge of DNA replication with this quiz that covers key concepts such as the role of enzymes, the fidelity of replication, and characteristics of leading and lagging strands. Understand the processes involved and the particulars of DNA polymerase functions, particularly in E. coli. Challenge yourself and see how well you grasp this fundamental biological process!