TE buffer, short for Tris-EDTA buffer, is a foundational solution in molecular biology, primarily utilized for the storage and handling of genetic material like DNA and RNA. Its specific formulation is designed to preserve the integrity of these molecules over extended periods, making it an indispensable tool for long-term archiving of genetic samples. The buffer’s name identifies its two main components: Tris, which stabilizes the solution’s acidity, and EDTA, which protects the DNA from enzymatic breakdown.
The Role of Tris: pH Stability
Tris, chemically known as Tris(hydroxymethyl)aminomethane, provides the buffer’s stability against changes in acidity or alkalinity. DNA requires a slightly alkaline environment, typically around pH 8.0, to prevent chemical degradation called hydrolysis. At lower, more acidic pH levels, the bonds holding the DNA’s chemical bases to its sugar backbone can break, leading to the loss of genetic information through depurination.
The Tris molecule resists fluctuations in hydrogen ion concentration, which can occur naturally over time or with changes in temperature. This capability prevents the solution from becoming too acidic, which would otherwise destabilize the DNA structure. Maintaining a stable, slightly alkaline pH ensures the DNA remains in its intact double-stranded form.
The Role of EDTA: Preventing Degradation
The second component, EDTA (Ethylenediaminetetraacetic acid), serves a protective role by preventing the biological degradation of the DNA. EDTA is known as a chelating agent, meaning it forms a tight, cage-like structure around metal ions in the solution. Specifically, it targets and binds to divalent cations, such as magnesium ions (\(text{Mg}^{2+}\)).
Removing these \(text{Mg}^{2+}\) ions is significant because they are necessary cofactors for a class of destructive enzymes called DNases. DNases break down DNA by cleaving its phosphodiester bonds. By sequestering the required \(text{Mg}^{2+}\) ions, EDTA effectively inactivates any residual DNases that may have contaminated the sample during the DNA extraction process. This neutralizes the biological threat to the DNA.
Why This Mixture is Essential for DNA Storage
The combination of Tris and EDTA provides a synergistic protective effect that far surpasses the capabilities of storing DNA in simple sterile water. While nuclease-free water is sometimes used for short-term storage, it lacks the buffering capacity to resist \(text{pH}\) changes and offers no protection against enzyme activity. TE buffer is therefore the preferred medium for long-term DNA archives, where maintaining the molecule’s integrity for years or decades is the goal.
The mixture is commonly used to resuspend purified DNA samples following extraction, preparing them for subsequent molecular applications like Polymerase Chain Reaction (PCR), gene sequencing, or cloning. The standard concentration used in TE buffer (typically 1 \(text{mM}\) EDTA and 10 \(text{mM}\) Tris) is generally low enough to be diluted out during the experimental process. High concentrations of EDTA can potentially interfere with downstream enzymatic reactions that also require \(text{Mg}^{2+}\). Low TE variations, which contain ten times less EDTA, are also employed when the DNA will be immediately used in highly sensitive applications to minimize any potential interference with the required cofactors.