Define plaque, lysogeny, and prophage.
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
5. Genetics of Bacteria and Viruses
Bacteriophage Genetics
Problem 15
Textbook Question
If a single bacteriophage infects one E. coli cell present on a lawn of bacteria and, upon lysis, yields 200 viable viruses, how many phages will exist in a single plaque if three more lytic cycles occur?

1
Understand the problem: A single bacteriophage infects an E. coli cell, producing 200 viable viruses after one lytic cycle. The question asks how many phages will exist after three additional lytic cycles, assuming each phage produced in one cycle infects a new cell in the next cycle.
Define the key concept: Each lytic cycle results in a multiplication of the number of phages by a factor of 200. This is an example of exponential growth, where the number of phages increases by a factor of 200 in each cycle.
Set up the formula: The total number of phages after n lytic cycles can be calculated using the formula \( N = N_0 \cdot 200^n \), where \( N_0 \) is the initial number of phages, \( n \) is the number of cycles, and \( N \) is the total number of phages after \( n \) cycles.
Substitute the known values: Here, \( N_0 = 1 \) (since we start with one phage), and \( n = 4 \) (one initial cycle plus three additional cycles). The formula becomes \( N = 1 \cdot 200^4 \).
Simplify the expression: Calculate \( 200^4 \) to determine the total number of phages after four lytic cycles. This will give the final answer.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Bacteriophage Life Cycle
Bacteriophages, or phages, are viruses that infect bacteria. Their life cycle typically includes attachment to a bacterial cell, injection of genetic material, replication of viral components, assembly of new virions, and lysis of the host cell to release new phages. Understanding this cycle is crucial for predicting how many phages will be produced after multiple infection cycles.
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Bacteriophage Life Cycle
Lytic Cycle
The lytic cycle is a type of viral replication where the virus takes over the host cell's machinery to produce new virions, ultimately leading to the destruction of the host cell. Each lytic cycle results in the release of a specific number of new phages, which can then infect additional cells. This concept is essential for calculating the total number of phages produced after several cycles.
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Decision Between Lytic and Lysogenic Cycles
Plaque Formation
A plaque is a clear zone on a bacterial lawn where phages have lysed the bacteria, indicating viral activity. The number of plaques correlates with the number of infectious phages present. Understanding how phages multiply and form plaques helps in estimating the total number of phages produced after multiple lytic cycles, as each cycle exponentially increases the phage population.
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Plaques and Experiments
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