11. Which of the following is false about freeze-fracture technique?
A. It involves physical breaking of frozen biological samples
B. Fixation in glutaraldehyde
C. Involves vacuum sublimation of ice
D. Cryoprotection with glycerol
Correct Answer: B. Fixation in glutaraldehyde
The freeze-fracture technique is false regarding glutaraldehyde fixation because it relies on rapid freezing of unfixed or minimally processed samples to preserve native ultrastructure, avoiding chemical fixatives that could alter membrane proteins or create artifacts.
Option Analysis
A. Physical breaking of frozen biological samples
This is true—samples are snap-frozen then fractured at -100°C or lower using a cooled knife, exposing internal membrane faces (P-face, E-face) for replication.
B. Fixation in glutaraldehyde
This is false—standard freeze-fracture skips chemical fixation like glutaraldehyde to maintain native hydration and protein distribution; fixation is optional only for specific pathogen-safe protocols.
C. Vacuum sublimation of ice
This is true—in freeze-etching (a variant), vacuum at -90°C to -100°C sublimes surface ice, revealing etched details before replication.
D. Cryoprotection with glycerol
This is true—glycerol (20-30%) prevents ice crystal damage during freezing, ensuring clean fractures through hydrophobic membrane interiors.
Introduction to False About Freeze-Fracture Technique
The false about freeze-fracture technique question tests if you know it avoids chemical fixatives like glutaraldehyde, prioritizing rapid freezing for native membrane views in electron microscopy.
Core Freeze-Fracture Steps
Samples get cryoprotected (glycerol), plunge-frozen, fractured under vacuum, optionally etched (ice sublimation), then platinum-carbon shadowed for TEM replicas. No routine fixation.
Technique Features Table
| Feature | True/False | Explanation |
|---|---|---|
| Frozen sample breaking | True | Exposes P/E-faces at -110°C |
| Glutaraldehyde fixation | False | Avoided for artifact-free imaging |
| Vacuum ice sublimation | True | Freeze-etching step |
| Glycerol cryoprotection | True | Prevents ice crystals |
GATE Life Sciences Tips
For false about freeze-fracture technique, remember: rapid freeze → fracture → etch → replicate. Skip fixation in answers. PYQs often contrast with TEM prep.
Research Value
Reveals intramembrane particles (proteins) in native state, key for membrane biophysics and cell biology studies. Modern cryo-variants enhance resolution.
