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Chapter 22: Problem 21

Bacteriophage T4 mutants defective in genetic recombination usually show defective DNA replication as well. What specific defect might you expect to see? Describe a plausible explanation for this effect.

Short Answer

Expert verified
The defect is stalled replication forks, leading to incomplete DNA replication.

Step by step solution

01

Understanding genetic recombination

Genetic recombination involves the exchange of genetic material between DNA molecules. In bacteriophages, this process is important for correct DNA replication and repair.
02

Connection between recombination and replication

During DNA replication, replication forks can encounter damages or blocks that stall the process. Genetic recombination provides mechanisms to repair these issues, allowing replication to continue.
03

Impact of defective recombination

If a bacteriophage T4 mutant is defective in genetic recombination, it may not effectively repair stalled or damaged replication forks. This can lead to incomplete or failed DNA replication.
04

Specific defect expected

The specific defect you might expect includes accumulation of non-viable phage particles, reduced replication efficiency, and potential genome instability due to unresolved replication forks.
05

Plausible explanation for the defect

The defect occurs because recombination machinery helps to stabilize and restart stalled replication forks. Without functioning recombination mechanisms, these processes cannot proceed efficiently, leading to replication failures.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

DNA replication
DNA replication is a crucial process where the DNA molecule makes a copy of itself. This process ensures that each daughter cell receives a complete set of genetic information during cell division. The replication process involves several key steps:
  • Unwinding of the DNA double helix by helicase.
  • Formation of the replication fork where the two DNA strands are separated.
  • Synthesis of the new DNA strands by DNA polymerase, which adds nucleotides complementary to the template strand.
Errors in replication can lead to mutations, which may be harmful to the organism. Thus, maintaining the fidelity of DNA replication is vital for genetic stability and overall organismal health.
bacteriophage T4
Bacteriophage T4 is a type of virus that infects bacteria, specifically Escherichia coli. It is a widely studied model organism in molecular genetics due to the simplicity and efficiency of its genetic mechanisms.
  • T4 follows a lytic lifecycle, quickly taking over the host cell's machinery to replicate its DNA and produce new phage particles.
  • It has a large, linear double-stranded DNA genome that encodes for various proteins crucial in DNA replication and repair.
  • Bacteriophage T4 is noteworthy for its sophisticated recombination processes, which are essential for repairing DNA damage and ensuring replication completion.
Research on T4 has greatly enhanced our understanding of genetic recombination and DNA repair mechanisms in more complex organisms.
replication forks
Replication forks are Y-shaped structures that form during DNA replication. They mark the points where the DNA double helix is unwound and new strands are synthesized. Key features of replication forks include:
  • Helicase enzymes that unwind and separate the DNA strands.
  • Leading and lagging strands, where continuous and discontinuous synthesis occurs, respectively.
  • Stalling can occur if replication forks encounter obstacles, such as DNA damage.
Efficient repair and restart of stalled forks are necessary to prevent interruptions in DNA replication, which is where genetic recombination plays an essential role. Ensuring smooth replication fork progression is vital to prevent errors and maintain genetic stability.
genome instability
Genome instability refers to the increased tendency for changes in the genome, including mutations, deletions, duplications, and rearrangements. It can lead to various genetic disorders and is a hallmark of cancerous cells. Causes of genome instability include:
  • Errors in DNA replication or repair.
  • Unresolved DNA damages, leading to replication fork stalling.
  • Defective recombination processes that fail to repair DNA accurately.
In bacteriophages like T4, effective recombination is crucial to avoid genome instability. If replication forks are improperly resolved, the phage DNA can accumulate mutations, potentially leading to non-viable particles or impaired functioning. Maintaining genome stability is therefore critical for the viability and propagation of organisms.

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Most popular questions from this chapter

In mammalian cells, genes that are expressed in a particular cell are reported to undergo replication during the first half of \(S\) phase, and genes not expressed in that cell are replicated in the latter half of S phase. Briefly describe an experiment that could lead to this conclusion. You might consider approaches that involve 5 -bromouracil incorporation.

Describe an experimental approach to determining the processivity of a DNA polymerase (i.e., the number of nucleotides incorporated per chain per polymerase binding event).

A major difficulty in preparing vaccines against viral diseases is the rapidity with which the virus mutates to vaccine resistance. What is the likely mechanism for this hypermutability? Would you expect this problem to affect DNA and RNA viruses equally? Explain.

The \(3^{\prime}\)-exonuclease activity of \(E\). coli DNA polymerase I was found to show no discrimination between correctly and incorrectly base-paired nucleotides at the \(3^{\prime}\)-terminus; properly and improperly base-paired nucleotides are cleaved at equal rates there. How can this observation be reconciled with the fact that the \(3^{\prime}\)-exonuclease activity increases the accuracy with which template DNA is copied?

Although DNA polymerases require both a template and a primer, the following single-stranded polynucleotide was found to serve as a substrate for DNA polymerase in the absence of any additional DNA. 3' HO-ATGGGCTCATAGCCGGAGCCCTAACC- GTAGACCACGAATAGCATTAGG-p \(5^{\prime}\) What is the structure of the product of this reaction?
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