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Overview of Marketing and Peer Review in Science

  • Marketing Process for Scientific Communication
    • An author wrote marketing for a book as a blog.
    • Invited comments from scientists on the validity of the story.
    • The process led to an unofficial peer review before book publication.
  • Implications:
    • Enhances the plausibility of information presented in the book.
    • Encourages collaborative and open dialogue in scientific writing.

Upcoming Assignments

  • Annotated Bibliography

    • Due next week.
    • Students must read through submitted PDFs now.
    • Example of annotated bibliography is available on Canvas for structure and length reference.

  • Final Video Project

    • Must incorporate information from at least three primary, peer-reviewed articles.
    • Focus on engaging presentation styles, including pop culture references.

  • Student Learning Outcomes (SLO) Modification

    • Students must differentiate between eukaryotic microbes and non-eukaryotic microbes for the upcoming test.
    • Focus should not just be on eukaryotes like Toxoplasma and Plasmodium.

Introduction to Hemotaxis and Chemotaxis

  • Chemotaxis: Movement of organisms in response to chemical gradients.

    • Organisms must be able to sense these gradients from a distance.
    • Example analogy: Sensing the smell of pizza from a distance leads one to navigate toward it.

  • Hemotaxis: Specific chemical navigation actions in bacteria.

    • Example: Importance of bacteria sensing sugar versus harmful substances (heavy metals, antibiotics).

  • Experimental Design:

    • Use of capillary tubes to observe bacterial movement towards attractants and away from repellents.

Mechanisms of Bacterial Movement and Sensing

  • Mechanics of Movement:

    • Single-cell eukaryotes have receptors for environmental signals that allow them to sense chemical gradients.
    • Bacterial cells are too small to sense gradients spatially; they utilize a temporal method of sensing to navigate.

  • Flagellation in Bacteria:

    • Peritrichous flagellation allows for random movement and directional changes.
    • Flagella work collectively as one motor for motion; they separate for tumbling.

  • Run and Tumble Mechanism:

    • Bacteria can run when moving in favorable conditions and tumble (change direction) based on environmental cues.

Sequence of Events in Chemotactic Responses:

  1. Movement Direction:
    • Attractant presence leads to prolonged runs (counterclockwise flagellar rotation).
    • High repellent concentrations trigger tumbles (clockwise rotation).
  2. Altering Tumble Frequency:
    • Bacteria adjust the frequency of tumbles based on environmental feedback.
    • More tumbles result from being in unfavorable regions.
  3. Temporal Sensory Mechanism:
    • Bacteria compare the current environment to previous conditions to decide on movement.
    • Temporal memory assists single-celled organisms in fine-tuning movement based on recognized substances.

Two-Component Chemotaxis Signal Transduction System

  • Major players in bacterial chemotaxis include specific proteins that function in the detection and response to chemical gradients:

    • MCPs (Methyl-accepting Chemotaxis Proteins):

    • Bind attractants and repellents; crucial for sensing.

    • Affinity changes when methylated or not methylated.

    • Sensor Kinases:

    • Main sensor kinase (KeyA) integrates various MCP signals.

    • Can auto-phosphorylate based on environment (presence of attractants or repellents affects phosphorylation rate).

    • Response Regulators (KeyY and KeyB):

    • KeyY leads to tumbling when phosphorylated; interacts with flagellar motors.

    • KeyB demethylates MCPs, altering their sensitivity to environmental signals.

    • KeyZ:

    • Dephosphorylates KeyY, regulating tumble rates.

    • KeyR:

    • Methylate MCPs, maintaining sensitivity regulation.

MCP Functionality and Recognition of Signals

  • Affinity Adjustments:
    • If MCP is methylated, affinity for repellent increases; less attraction affinity leads to more tumbling when repellent is present.
    • Conversely, non-methylated MCP increases affinity for attractant, leading to longer runs in the right direction.

Feedback Mechanisms in Chemotaxis

  • Phosphorylation Dynamics:

    • Changes in the phosphorylation of KeyY and KeyB determine the response to environmental conditions (repressive or stimulatory).

  • Signal Processing:

    • The bacteria's ability to sense environmental changes is dynamic and based on the methylation status of MCPs, leading to varied responses to fluctuating concentrations of attractants and repellents.

  • Limitations and Adaptations:

    • Bacterial cells constantly need to recalibrate based on environmental shifts; hence, their mechanisms allow them to respond effectively to the conditions around them, favoring survival strategies by tuning their movement appropriately.

Conclusion and Review Task

  • Understanding Chemotaxis:
    • Draw mixed concentration gradients of attractants and repellents, placing bacteria in the center to visualize movement responses.
    • Sequence through step-by-step how the system responds falls upon attractants and repellents, reinforcing knowledge of bacterial navigation mechanisms.
  • Practice Scenarios:
    • Create situations to predict movements, decisions, and adaptations by bacteria in various chemical environments, solidifying the grasp of the chemotactic response.