Lab Eight Study Guide

Lab Eight Overview

• This lab focuses on the effects of the herbicide Roundup on yeast fermentation processes and spectrophotometric techniques in microbiology.

Review Questions from Previous Labs

• Introductory discussion of yeast fermentation and its application in brewing.
    - Brewer's Yeast: Used to ferment sugars in barley to create beer.
    - Fermentation Issues: NOSA, a brewery owner, noticed a decline in fermentation efficiency after changing barley suppliers, hypothesizing pesticide contamination as the cause.

NOSA's Hypothesis Testing

• Hypothesis: The herbicide Roundup inhibits enzymes involved in the fermentation process of converting pyruvate to ethanol.
• Methodology: Using spectrophotometry and applying a chromophore that absorbs at 504 nm when exposed to ethanol to test enzyme activity.
• Experimental Design: Data collected in triplicate for accuracy.

Initial Data Interpretation

• Graph interpretation question: What can be concluded from the initial data?
    - Options:
      - A) Roundup inhibits one or both enzymes.
      - B) Roundup does not inhibit either enzyme.
      - C) Neither of the above (maybe data is inconclusive).
    - Correct Answer: C (inconclusive data).
• Reasoning: Lack of knowledge on normal pathway activity affects conclusions.

Main Reason for Lack of Conclusions

• Choice explanation: B) Lack of controls.
    - Rationale: Error bars are not helpful without controls; controls were indeed not run in the experiment.

Improved Graph with Controls

• Negative Control: Called a vehicle, it contains the solution carrying Roundup but not Roundup itself, matched for pH and other conditions.
• Conclusions drawn from this better graph:
    - A) Roundup does not inhibit either enzyme.
    - B) Roundup inhibits one or both enzymes completely.
    - C: Roundup inhibits one or both enzymes partially.
    - D: Vehicle inhibits one or both enzymes more than Roundup.
• Correct Conclusion: C (Roundup partially inhibits enzyme activity as indicated by absorbance changes).

Absorbance Changes

• The absorbance of chromophore increases over the reaction course:
    - Experiment showed absorbance increases, contrasting past experiments that showed decreases.
• The graph demonstrated a relationship between absorbance and another variable.

Possible X-Axis Variables

• Options presented:
    - A) Time
    - B) Transmittance
    - C) Absorbance wavelength
    - D) Chromophore concentration
• Likeliest and Correct Answer: D (Chromophore concentration).

Spectrophotometry and Beer-Lambert Law

• Beer Lambert equation: $A = ext{Epsilon} imes C imes L$
    - Where: A = absorbance, Epsilon = extinction coefficient, C = concentration, L = path length.
• Given specific wavelengths (504 nm), constants yield an effective line equation.
• Y-intercept understanding: The equation indicates values intersecting the y-axis at zero (where absorbance starts).

Application of Beer-Lambert Law to Crystal Violet

• Scenario: Measuring concentration of crystal violet for Gram staining.
• Parameters:
    - Desired Concentration: 10 micromolar.
    - Measured absorbance at 590 nm: 0.87.
    - Extinction coefficient: 87,000 $L/(mol imes cm)$.
• Path Length: Set at one cm.

Conversion and Calculation Steps

• Awareness of units: Convert extinction coefficients from $L/(mol imes cm)$ to $ext{liters}/( ext{micromoles} imes ext{centimeter})$ for proper calculation.
• Conversion factor: $1 ext{ mole} = 10^6 ext{ micromoles}$ results in revised coefficient of $0.087 L/( ext{micromole} imes ext{cm})$.
• Final calculation: Using the Beer-Lambert equation, substituting variables to find concentration.

Calculation Steps

1. Rearranging: We need to solve for concentration C.
2. Using the adjusted extinction coefficient, solve:
      C = rac{A}{ ext{Epsilon} imes L} = rac{0.87}{0.087}
3. Resulting concentration: 10 micromoles per liter or 10 micromolar, confirming the accurate concentration.

Spectrophotometric Analysis in DNA and Protein Quantification

• Importance of measuring DNA and protein concentrations post-purification.
• Absorption Peaks:
    - DNA: 260 nm
    - Proteins: 280 nm
• Correct Answer Selection: Ratio usage significance and acceptable values for purity determinations in lab settings.

Bacterial Transformation Experiment Preparation

• Shift to transforming enzyme-deficient bacteria with purified genomic DNA from prior lab.
• Focus on following sterile techniques to avoid contamination during experiments.

Sterilization Techniques

• Clean workspace: 70% ethanol is the correct choice for disinfecting.

Sample Preparation

• Preparation of microcentrifuge tubes: Labeled appropriately from 1-8, considering controls.
• Control Types:
    - Positive control: TRP+ donor cells.
    - Negative control: TRP- recipient cells, indicating an auxotrophic strain.

Transformation Procedure

• Importance of adding saline citrate first, careful addition of recipient cells last.
• Handling Recipient Cells: Quick thawing approach ensuring the vitality of fragile cells.

Agar Plate Preparation

• Bacterial growth medium preparation: Tryptophan presence in selective media (TRP+ vs TRP-).
• Labeling and incubaion procedures specified for isolation of results post-experimentation.

Sample Plating

• Pipetting techniques: precision is crucial to prevent contamination during streaking on agar plates.
• Control identification on plates based on growth or lack of growth following transformation.

Cleanup Procedures

• Disposal of biological materials in biohazard containers mandatory.
• Final organization and restocking of materials post-experiment.

Key Data Analysis for Lab Report

• Images provided for lab report analysis: five lanes indicating various controls and experimental groups.
    - Identification of negative controls: Expectation of non-growth in specific groups.

Summary of Key Points

• Comprehensive understanding of methodologies and principles in spectrophotometry and microbial transformation.
• Importance of controls, precise measurements, and practical applications in biological experiments for conclusive outcomes.