Microbiology Exam Review: Key Concepts and Quiz Discussion

Quiz Corrections & Key Concepts

  • Pasteurization: The statement that pasteurization requires cooling the desired food to a particular temperature is false.

  • Aerobic vs. Anaerobic Bacteria: Aerobic bacteria cannot grow in the presence of oxygen is stated as false, implying aerobic bacteria can grow in the presence of oxygen. Anaerobic bacteria cannot.

  • Dr. Semmelweis's Policy: Dr. Semmelweis instituted a policy using a chlorine solution in an attempt to reduce paternal deaths.

  • Biofilm: A biofilm is defined as a community of microbes that is strongly bonded together in a matrix of polysaccharides.

  • Ecosystem Nutrient Levels:

    • Oligotrophic: Refers to natural ecosystems that are typically low in nutrients.

    • Eutrophic: Describes environments with many nutrients; it is the opposite of oligotrophic.

  • Programmed Cell Death (PCD): One function of programmed cell death is described in the context of nutrient limitation, where cells might be sacrificed for the broader community.

  • Gram-Positive Bacteria and Endospores: Gram-positive bacteria that form endospores.

  • Desiccation: The spelling of desiccation is confirmed as d-e-s-i-c-c-a-t-i-o-n.

  • Quorum Sensing in Biofilms: Quorum sensing is triggered in biofilms when the population reaches a certain number.

  • Spontaneous Generation Theory: This theory was prevalent prior to the germ theory.

  • Ribosomes: All known microorganisms have a set of genes coding for ribosomes whose RNA sequences are highly conserved across the phylogenetic tree.

  • Polar Microbe Adaptations: An adaptation expected for polar microbes in their membranes would be unsaturated fatty acids.

Antibiotics and RNA Polymerase

  • Rifamycin vs. Actinomycin B:

    • Rifamycin: Functions as an antibiotic by specifically targeting the exit of the mRNA on a bacterial RNA polymerase. It is specific to bacterial RNA polymerase, making it a viable antibiotic for human infections.

    • Actinomycin B: Acts like a DNA base, mimicking DNA to prevent transcription. It binds to single-stranded DNA and is not specific to bacterial DNA, thus affecting human cells as well and making it harmful.

  • Designing Antibiotics: When designing an antibiotic to treat human infection, potential targets on the bacterial RNA polymerase molecule include:

    • The binding site.

    • Sigma factors, as these are specific to bacteria and would not affect human cells.

    • The RNA exit channel (as targeted by rifamycin).

  • Archaea and RNA Polymerase:

    • Archaea typically do not cause human disease.

    • Treating an archaeal infection by targeting its RNA polymerase would be a good strategy because archaea only have one RNA polymerase.

    • Structurally, archaeal RNA polymerase is more similar to a eukaryotic polymerase than a bacterial polymerase. This structural similarity suggests that targeting archaeal RNA polymerase, even if effective against the single polymerase, could potentially have off-target effects on human eukaryotic polymerases.