Definition of Gel Electrophoresis System
It is a method used in laboratories that separates and analyses biomacromolecules including DNA, proteins, and RNA, according to their size and charge. Molecules transport across the gel, using an electric field, having smaller or differentially charged molecules moving faster and farther than bigger ones. It is a commonly used technique in molecular biology and biochemistry for various purposes, such as DNA fragment analysis, molecular characterization, and protein separation.
Introduction
Gel electrophoresis is a commonly utilized laboratory technique for separating and analyzing biomacromolecules like RNA, DNA, and proteins. It is based on electrophoresis, which includes the movement of charged particles in a solution towards an opposing electrode according to the electric field. Arne Tisselius, a Swedish biophysicist, developed the notion of electrophoresis in the 1930s while examining blood proteins. Tisselius’ revolutionary research in electrophoresis earned him fame and the Nobel Prize.
The application of gels in electrophoresis offers many purposes. Primarily gels serve as an anticonvective medium, reducing thermal convection generated by applying an electric field. This allows for a more controlled and precise separation procedure. Furthermore, gels function as a filtering medium, delaying the passage of molecules dependent on their size.Gels also provide a rigid support structure for the molecules following electrophoresis, enabling post-electrophoresis labeling or further characterization by RFLP, mass spectrometry, PCR, DNA sequencing, cloning, and Southern blotting.
Principle of Gel Electrophoresis
The gel electrophoresis principle is that biomolecules, like DNA, proteins, and RNA have electric charges because of their ionized functional groups. Depending on the pH, these functional groups give the positively or negatively charged ions in a solution that contains biomolecules,
When a solution containing charged biomolecules is exposed to an electric field, the molecules migrate in the opposite direction of the positive or negative pole. The migration rate of each molecule is determined by its net charge and mass. Negative charged particles, nucleic acids travel towards the anode, whereas positively charged particles flow towards the cathode. Based on mass and charge, this differential migration enables the separation of biomolecules with comparable characteristics.
Gels are used as a support matrix, to eliminate the limitations of previous support matrices utilized for zone electrophoresis. Zone electrophoresis involves mixing liquid samples with a Loading Buffer before applying them to a specified zone on the gel matrix which is pre-soaked with a running buffer of electrophoresis. Once the electric field is used, the molecules migrate across the gel. When the desired separation reaches, the electric field is withdrawn.
During migration, molecules with the same characteristics form distinct bands on the gel matrix. This distinction depends on variations in migration rates, established by their specific characteristics. Following electrophoresis, stain the gel matrix to see the separated bands, enabling additional quantitative investigation.
Parts of Gel Electrophoresis Apparatus
Power supply
It is an important component of gel electrophoresis systems, delivering a consistent and controlled electric current to aid in the migration of charged biomolecules across the gel matrix. Electrophoresis requires a steady power supply. This power supply is linked to the gel box by lead wires that are usually color-coded i.e. red (anode) and black (cathode).
The power supply transmits electric current from the power source to the gel box via these connections. The right polarity must be maintained throughout the connection. In a gel electrophoresis system, the negatively charged DNA and RNA molecules move toward a positively charged electrode. As a result, the black wire is connected to the back of the gel box, allowing the molecules to migrate to the front, where the positively charged red wire is connected.
It is essential to use a constant power supply to minimize electrical current fluctuations that can disturb the separation process or affect the results. When the current flow in the gel increases, it also raises the resistance, which produces greater heat. This heat can promote thermal agitation of the dissolved ions in the buffer, resulting in greater water evaporation from the apparatus. Therefore, the concentration of ions in the buffer can increase.
Buffers
Buffers are important components of many analytical and scientific processes, especially in chemistry, biology, and biochemistry. They are essential for regulating the pH of a system and modulating the electrical charge of solutes.
One of the fundamental functions of a buffer is to maintain the ability of the analyte to dissolve. It prevents the analyte from precipitating or aggregating, which could interfere with detection or change its behavior.
There are two types of buffers: acidic and basic. Acidic buffers such as citrate, formate, phosphate, and acetate are utilized to maintain a lower pH. In contrast, basic buffers like tris, tricine, and borate are used to maintain high pH levels. The proper buffer is chosen based on the required pH range and the analytical needs.
Buffers are composed of monovalent ions to ensure the system’s pH and modulating the solutes’ electrical charge and uniform valency (or ionic strength). This composition guarantees that the buffering capacity remains stable and consistent. However, prepared buffers should be handled with care, especially when not in use. Buffers should be refrigerated to prevent bacterial growth, as they might provide an ideal environment for contamination by microbes.
The utilization of cold buffers has several advantages. First, it improves sample resolution, which leads to better analyte separation and detection. Furthermore, the cool temperature reduces solvent evaporation, ensuring that the analytes remain intact and concentrated throughout the analysis. Buffers are reused i.e. up to 4 times, if prepared in large quantity. In the case of lesser volumes or for crucial applications, it is best to dispose of the buffer after one usage. Reusing buffers increases the danger of contamination and degradation, which may reduce the accuracy of the results.
It is vital to highlight that heat-labile substances are in danger due to the high temperatures produced during certain operations. However, the greater ionic strength of a buffer can help achieve better resolution. A careful balance should be provided for the preservation of the integrity of the analyte and obtaining the required separation.
Support media
Support media play an important role in many scientific and analytical procedures, assisting in separating and evaluating molecules. These media, which include polyacrylamide, starch, cellulose acetate, and agarose membranes, act as a scaffold or matrix, facilitating the separation process.
Support media are distinguished by their high water content, which usually exceeds 90%. This property is important because it permits the media to retain its structure and permeability, allowing molecules to separate. The high water content keeps the media hydrated and is an ideal molecular filtration condition.
These media act as molecular sieves, enabling only specific molecules to pass depending on their size. Small molecules can diffuse through the porous support media, whereas bigger molecules are impeded and cannot move through it. This differential permeability is vital for many applications, like chromatography and electrophoresis.
These media must be electrically neutral to enable precise separation and minimize undesirable interactions. This neutrality aids in the prevention of electrical charges influencing the migration and binding of molecules inside the media. The support media maintains a neutral environment, ensuring that separation procedures are predominantly influenced by molecular size and other appropriate factors instead of electrical forces.
Agarose gel is one of the most preferred support media for electrophoresis. Agarose, a polysaccharide produced from seaweed, forms a gelatinous matrix when combined with water. During electrophoresis, this gel structure is a stable medium for separating biomolecules according to their size and charge. Agarose gel electrophoresis is commonly used to analyze RNA, DNA, and proteins in various domains, such as molecular biology, biochemistry, and genetics.
The unique requirements of the separation technique and the nature of the molecules under investigation determine the particular kind of media utilized. Different media have variable pore sizes and gel strengths, allowing researchers to adapt separating conditions to their unique requirements.
Starch Gel
This is historically noteworthy since it was the first gel medium used in electrophoresis. Starch gel made it easier to separate proteins based on molecular size and charge-to-mass ratio.
Form a colloidal suspension by boiling a combination of starch granules in a buffer solution to make a starch gel. Once the suspension cooled down, the starch chains, especially the branched chains of amylopectin, interweave, forming a semisolid gel matrix. This gel matrix provides the essential support to separate proteins during electrophoresis.
Using petroleum jelly prevents unwanted outcomes like gel matrix swelling or shrinkage. This addition improves the stability and uniformity of the gel, allowing for accurate protein separation.
Starch promotes the development of sharp zones, which allows for easy separation between distinct protein bands. The gel also has great resolving power, which enables it to successfully separate proteins with comparable molecular weights but varied charge-to-mass ratios.
Regardless of its benefits, the usage of starch gel decreases over time. One of the key reasons for this drop is the difficulty of creating the gel in a reproducible manner. Accurate gel preparation may prove difficult, resulting in varying separation results. This lack of reliability has motivated researchers to look into other gel media that are more consistent and reliable.
As a result, polyacrylamide and agarose gels are increasingly used in current electrophoresis procedures. These media provide enhanced reliability, simplicity of preparation, and greater control over gel properties, resulting in more consistent and reliable results.
Agarose
Agarose is a natural linear polymer and is an important component of agar. It is derived from red seaweed. It is made up of 3,6-anhydro-galactose and galactose chains. After isolation, store Agarose as a dry powder.
To prepare Agarose gel, dissolve agarose powder in an appropriate buffer solution. Heat this solution for the complete dissolution of agarose powder. As the solution cools to room temperature, it hardens as a gel matrix. Determine the pore size of the resulting gel by the concentration of agarose in the solution buffer, making it an important factor in molecular separation.
Use Agarose gel to discriminate between DNA and RNA molecules, with concentrations range from 0.8% – 5% (W/V). This range enables successful separation according to the nucleic acid molecules’ size. Agarose gels typically provide lower resolution than polyacrylamide gels. However, they have many advantages that make them popular in gel electrophoresis applications. Agarose has a low gelling temperature, which means it solidifies at low temperatures, making it to use during the gel preparation. It also has a neutral charge, which prevents undesired interactions between charged molecules. Moreover, agarose produces stable gels, guaranteeing that the gel matrix remains intact during electrophoresis.
Versatility is another distinguishing feature of agarose. Utilize it in either solid or liquid form, depending on the purpose of the study requirements. In liquid form, agarose can be utilized in procedures such as pulsed-field gel electrophoresis, which separates large DNA fragments.
Cellulose Acetate
There is an extensive use of Cellulose acetate in the electrophoresis methods development, especially for the separation of proteins. Kohn used it first time for hemoglobin separation and the detection of irregular protein forms in blood serum.
Cellulose acetate is generated from cellulose, a naturally occurring polymer present in plant cell walls. To form cellulose acetate, acetylate the filter sheets made completely of cellulose. Acetylation is the process of adding acetyl groups to specified sites on the glucose rings of cellulose, often at the C-3 and C-6 positions.
Compared to other regularly used electrophoretic matrices such as polyacrylamide and agarose, cellulose acetate pores are bigger. This indicates that the gel matrix created by cellulose acetate facilitates separation of molecules according to their size. The bigger pores allow proteins and other biomolecules to travel more easily across the gel, resulting in successful separation.
Cellulose acetate electrophoresis has many applications, such as research and clinical diagnostics. It has benefits like cost-effectiveness, quicker separation, and simplicity than other approaches. The bigger pores in cellulose acetate gels also detect some proteins that would otherwise be difficult to separate utilizing matrices having smaller pores.
Other matrices, like agarose and polyacrylamide, have grown in popularity in recent years because of their higher resolution and application flexibility. Although cellulose acetate remains a viable medium for particular uses, especially if there is a need for bigger pore sizes or if the target is particular biomarkers or proteins.
Polyacrylamide
It is a gel matrix frequently utilized in electrophoresis, especially for proteins and DNA separation. It is produced by copolymerizing acrylamide monomers in the presence of “bis-acrylamide” or N, N-methylene bis-acrylamide (also known as crosslinking agent). The final gel is transparent as well as clear.
The acrylamide concentration determines the size of holes in polyacrylamide gels. The concentration must be proportional to the amount of crosslinking agent utilized. Adjusting the acrylamide concentration enables researchers to manipulate the pore size, which is essential for attaining the appropriate molecule separation on the basis of their size.
The acrylamide gel concentration in electrophoresis differs according to the target molecules and purpose. A small quantity of acrylamide gel is commonly used to separate DNA and proteins, ranging from 3% to 15%. This range is appropriate for properly separating molecules in the DNA and protein size range.
Proteins are separated using (SDS-PAGE) sodium dodecyl sulfate-polyacrylamide gel electrophoresis under denatured conditions, mostly based on size. This approach makes use of a larger acrylamide gel percentage, often ranging from 10% – 20%. The greater acrylamide concentration improves resolution as well as separation of proteins of various sizes, which aids in protein sample analysis.
Polyacrylamide gels have various advantages. They produce a stable and uniform gel matrix, allowing molecules to migrate. These gels are chemically inert and highly reproducible. Polyacrylamide gels are transparent, allowing for easy visualization and study of separated components.
It is worth mentioning that polyacrylamide gels are normally created by polymerization via a chemical process and must be handled with caution due to the acrylamide’s potential toxicity in its liquid state. After polymerization, the final gel matrix is safe for usage.
Electrophoresis chamber
It is an important part of the electrophoresis process since it provides an optimized environment for biomolecule analysis as well as separation. It usually includes a tank or plastic container containing a buffer solution.
The buffer solution performs several functions in the electrophoresis chamber. For instance, it establishes a conductive environment that allows charged biomolecules to migrate during electrophoresis. Second, it aids in maintaining a constant pH level that is essential for successful separation. Furthermore, the buffer solution aids in dissipating heat created during the electrophoresis process, protecting the gel matrix from overheating.
A remarkable characteristic of this chamber is having transparent lid, which allows researchers to examine the migration of biomolecules. The transparent lid allows researchers to observe the separation in real-time, making modifications as needed or assessing its progress.
The chamber is connected to a power supply, which supplies the necessary electrical current. The power supply provides an electric field, causing charged biomolecules to move through the gel matrix. The chamber is designed to distribute electrical current equally throughout the gel, resulting in reliable and reproducible results.
The design and dimensions of these chambers are dependent on the application and size of the gel. Some chambers intend horizontal electrophoresis, which involves placing the gel in a horizontal position between two electrodes. Some are built for vertical electrophoresis, which involves positioning the gel perpendicular between the electrodes. The type of electrophoresis, desired separation conditions, and sample size determine the chamber.
Electrodes
Electrodes are essential components in electrophoresis. These separate molecules according to their charge. There are two platinum electrodes, the anode and the cathode. The anode is positively charged, whereas the cathode is negatively charged. These electrodes generate an electric field, which moves charged molecules across the gel matrix.
Because of their opposing charges, these electrodes attract and bind ions with comparable charges. The difference in attraction guarantees that these electrodes propel differently charged molecules within the gel toward the electrode with the opposite charge.
The charged molecules travel to their respective electrodes according to their charge, as the electric current moves across the gel. This movement allows the biomolecules separation, like proteins or DNA fragments, based on their size or charge-to-mass ratio, depending on the method used.
Platinum electrodes are commonly used because of their high conductivity, corrosion resistance, and chemical stability. These qualities enable dependable and consistent performance throughout electrophoresis studies. Depending on the experimental demands, use other materials for electrodes, like stainless steel or gold.
Container for staining and de-staining gel
This is a vital tool in the gel electrophoresis process. It provides an appropriate setting for using staining reagents to visualize and analyze isolated biomolecules. Here are some important features of these containers:
• Perform gel staining and de-staining using trays and containers. Depending on the unique needs and preferences of the researcher, these containers can take numerous forms, such as boxes with or without lids.
• These containers are commonly made of polypropylene. Propylene, also known as polypropylene, is a long-lasting and chemically resistant substance that can tolerate exposure to a variety of staining reagents, stains, and chemicals utilized for gel electrophoresis research.
• These containers are notable for their transparency. This enables researchers to readily monitor and visualize the staining or de-staining processes without opening the container. The transparency allows for real-time monitoring and evaluation of the staining and destaining progress and strength.
• These containers frequently have close-fitting lids or covers. The tight-fitting lids avoid contamination and evaporation during the procedure. They establish an air-tight seal, to make sure the staining reagents and de-staining solutions have uninterrupted contact with the gel. They are chemical and stain-resistant. This resistance guarantees that the container stays operational and reliable over several trials.
Gel Caster and Comb
Gel casters and combs are vital equipment for preparing gel matrices. They serve an important function in forming wells inside the gel for loading of sample and maintaining the gel matrix integrity during the separation process. Here are some important features of gel casters and combs:
The gel caster acts as a container into which the gel is transferred and allowed to harden. It intends to hold the gel solution in a specific shape and size, resulting in uniform and accurate gel matrices. It is usually built of a long-lasting material like acrylic or glass that is suitable for the chemistry of gel.
After preparing the gel solution, transfer it to the gel caster, and place it into the electrophoresis device, where the gel solidifies or polymerizes according to the gel chemistry. The gel caster contributes to the formation of a homogenous gel matrix. Use this matrix as the medium for the separation of the sample.
The comb is an attachment that works in combination with the gel caster to produce wells inside the gel matrix. The comb is formed of a hard material like stainless steel or plastic, with equally spaced prongs or teeth. When put into the gel caster, these teeth puncture the gel, resulting in uniformly sized and spaced wells.
The comb determines the number of wells and their size. Diverse comb arrangements allow for the development of a variety of wells to meet various sample loading needs. To ensure the wells formation after the polymerization of gel, place the comb into the solution of gel before it solidifies.
The wells form by the comb act as designated regions for samples loading into the gel. Add samples like proteins or DNA fragments, into the wells by a pipette. The wells designate the locations where biomolecules separate during electrophoresis, making it easier to analyze and identify.
Gel casters and combs are specifically engineered to work with the gel chemistry in use, enabling optimal formation of gel and sample loading. These are reusable equipment that may be cleaned and sterilized between experiments to ensure hygiene and avoid contamination.
References
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