Blotting: How It Works and The Different Types

Overview of Blotting Techniques for the MCAT

  • Focus on interpretation of blots, method preparation briefly covered.

Major Steps in Blotting

  • Sample Separation:

    • Running a sample on a gel for size separation.

  • Transfer to Blotting Paper:

    • Pasting special paper on the gel to absorb samples.

  • Visualization of Samples:

    • Using antibodies to detect specific molecules.

Example: Detecting ADP and ATP

  • Procedure Breakdown:

    • Extract cytosol from cells and run on a gel.

    • Transfer gel content to blotting paper.

    • Expose blot to a marker for ATP and ADP detection.

  • Interpretation:

    • Larger molecules (e.g., ATP) appear higher on the blot than smaller ones (e.g., ADP).

    • Band thickness indicates quantity: thicker bands = more molecules.

    • Example Findings:

      • Cell C has the largest ATP (thickest band).

      • Cell A has more ATP than ADP, whereas Cell B has more ADP than ATP.

Key Takeaway

  • Larger molecules rise to the top during gel separation, and thicker bands signify greater quantities.

Sample Question Analysis: Truncated Titan and DCM

  • Context:

    • Truncated titan associated with dilated cardiomyopathy (DCM).

  • Interpretation Steps:

    • Identify truncated titan band (appears lower on the blot).

    • Patient with the thickest band of truncated titan is at the highest risk for DCM.

    • Conclusion:

    • Patient C has the highest amount of truncated titan.

Understanding Different Types of Blots

  • Types of Blots:

    • Southern Blots:

      • Measure DNA.

    • Northern Blots:

      • Measure RNA.

    • Western Blots:

      • Measure proteins.

  • Mnemonic for Recall:

    • "SNOW DROP" (S-DNA, N-RNA, W-Protein).

    • O serves as a placeholder.

Transcription and Translation Monitoring

  • Transcription (by Northern Blots):

    • Monitoring RNA production from DNA.

  • Translation (by Western Blots):

    • Monitoring protein production from RNA.

  • Scenarios:

    • Downregulation of translation shows normal RNA and low protein.

    • Downregulation of transcription shows low RNA and low protein.

Practice Questions on Blots

  • Question on HIV Detection:

    • Detect anti-HIV antibodies using a Western blot.

  • Question on Sonic Hedgehog Protein Production:

    • Determine the presence of transcription blockage using a Northern blot.

  • Error Scenarios:

    • Misclassification of blots in questions leads to incorrect answers.

Summary of Key Concepts

  • Understand the use of different blots to measure varying molecules:

    • Blot Hierarchy:

      • Southern Blots = DNA

      • Northern Blots = RNA

      • Western Blots = Proteins

  • Emphasize the importance of the size and thickness of bands in interpretation.