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Questions and Answers
What is the primary goal of performing serial dilutions and plate counts?
What is the primary goal of performing serial dilutions and plate counts?
Which of the following media types is used to assess genetic diversity in microbes?
Which of the following media types is used to assess genetic diversity in microbes?
Which of the following best describes how UV light damages bacterial DNA?
Which of the following best describes how UV light damages bacterial DNA?
Why does UV light kill endospores at a lower rate than vegetative cells?
Why does UV light kill endospores at a lower rate than vegetative cells?
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The principle that one bacterial cell can form one _____ on an agar plate.
The principle that one bacterial cell can form one _____ on an agar plate.
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A mutant bacterial strain may lose its ability to synthesize a particular amino acid due to disruption in the _____ pathway.
A mutant bacterial strain may lose its ability to synthesize a particular amino acid due to disruption in the _____ pathway.
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What is the final dilution factor after transferring 1 mL from a 10⁻⁶ dilution into a tube containing 9 mL of sterile saline?
What is the final dilution factor after transferring 1 mL from a 10⁻⁶ dilution into a tube containing 9 mL of sterile saline?
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What are pyrimidine dimers, and how do they affect DNA base pairing?
What are pyrimidine dimers, and how do they affect DNA base pairing?
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Study Notes
Serial Dilutions & Plate Count Lab
- Primary goal of serial dilutions and plate counts: Determine viable bacterial cell concentration in a sample.
- Principle of plate counting: One bacterial cell forms one colony on an agar plate.
- Creating a dilution: To create a 10⁻¹ dilution, transfer 1 mL of bacterial broth culture into 9 mL of sterile saline. To create a 10⁻² dilution, transfer 1 mL of the 10⁻¹ dilution into 9 mL of sterile saline.
- Dilution factor calculation: Transferring 1 mL from a 10⁻⁶ dilution into 9 mL of sterile saline results in a final dilution factor of 10⁻⁷.
- Calculating original bacterial concentration: Divide the number of colonies by the volume plated and multiply by the dilution factor. For example, 167 colonies from 0.1 mL of a 10⁻³ dilution gives ((167 colonies / 0.1 mL) * 10³) = 1.67 x 10⁶ viable cells/mL.
Genetic Diversity Lab
- Spontaneous mutations: Random changes in DNA sequence that occur naturally during DNA replication. They can be beneficial, harmful or neutral for the microbe.
- Media for assessing genetic diversity: YNB agar is used to assess genetic diversity in microbes.
- Wild-type strain: A bacterial strain that exhibits the typical characteristics of its species.
- Mutant strain: A bacterial strain that has a genetic alteration, resulting in a change in its phenotype.
- Amino acid synthesis disruption: Mutant bacterial strains may lose the ability to synthesize a particular amino acid due to disruption in the biosynthetic pathway of that amino acid.
UV Light Lab
- UV light damage on bacterial DNA: UV light forms pyrimidine dimers in DNA, which are covalent bonds between adjacent thymine or cytosine bases.
- Effect of pyrimidine dimers on DNA base pairing: Pyrimidine dimers distort DNA structure and hinder proper base pairing during replication, leading to mutations or replication errors.
- Lower UV killing rate in endospores vs. vegetative cells: Endospores have a lower rate of killing by UV light because they are less metabolically active and have DNA repair mechanisms.
- Endospore resistance to UV light: The thick spore coat and lower metabolic activity of endospores contribute to their resistance to UV light.
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Description
Explore the methods of serial dilutions and plate counts used to determine the concentration of viable bacterial cells in a sample. This quiz covers the principles, calculations, and techniques involved in accurately measuring bacterial concentration through dilution factors and colony counts.
