Which of the following method uses “Heat Shock”?
A. Transformation method
B. Cell lysis method
C. Molecule separation method
The correct answer and explanation is:
The correct answer is: A. Transformation method
Explanation:
Heat shock is a technique primarily used in molecular biology to introduce foreign DNA (such as plasmids) into bacterial cells, a process known as transformation. This method exploits a brief, controlled increase in temperature to make bacterial cell membranes more permeable, allowing the uptake of DNA molecules from the surrounding environment.
How Heat Shock Works in Transformation:
- Preparation of Competent Cells:
Bacterial cells (commonly E. coli) are first treated with calcium chloride (CaCl₂) or other chemical agents to make their cell walls temporarily more permeable. These cells are called competent cells because they are capable of taking up DNA. - Mixing with DNA:
The plasmid or DNA of interest is mixed with the competent cells on ice. - Heat Shock Step:
The mixture is then subjected to a short burst of elevated temperature, typically around 42°C for about 30 to 90 seconds. This sudden heat shock creates a thermal imbalance across the bacterial membrane, facilitating the entry of the DNA molecules into the cells. - Recovery:
After heat shock, cells are quickly returned to ice and then allowed to recover in nutrient-rich medium to express the antibiotic resistance or other markers carried by the plasmid, enabling selection.
Why Heat Shock Is Not Used in Other Methods:
- Cell lysis method (B):
Cell lysis involves breaking open cells to release their contents, such as proteins or nucleic acids. Methods include mechanical disruption, enzymatic digestion, or chemical detergents. Heat shock is not typically involved here because excessive heat can denature proteins and damage cellular contents. - Molecule separation method (C):
Molecule separation usually involves physical or chemical techniques like centrifugation, chromatography, or electrophoresis. Heat shock is not used to separate molecules.
Summary:
Heat shock is a key step in the transformation method for introducing DNA into bacteria. By briefly exposing competent cells to elevated temperature, it temporarily disrupts the membrane, allowing foreign DNA to enter the cell. This method is widely used in cloning and genetic engineering. It is not related to cell lysis or molecule separation techniques.