C. Protein Analysis Tools Flashcards
- Protein ______ tools and techniques enable one to separate proteins and subsequently identify them.
analysis
- Separation and identification methods include: (4)
- SDS-PAGE
- 2D-Gel Electrophoresis
- Isoelectric focusing (IEF)
- Western blot
- Separation and identification methods include: (4)
- SDS-PAGE
- 2D-Gel Electrophoresis
- Isoelectric focusing (IEF)
- Western blot
- Protein purification of methods include _________.
- Insulin is a protein that is produced in a lab for patients who cannot make it themselves. It is
important to use analysis tools to ensure the correct protein (_______) has been made and that it contains no other proteins that could be harmful to people.
chromatography
insulin
What does SDS-PAGE stand for?
- SDS-PAGE stands for Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis.
How does SDS-PAGE work? (5)
- A solid medium in the form of a gel is submerged in a buffer solution.
- The gel has wells on top in which a protein sample can be transferred using a pipette.
- Because the density of the protein sample is typically similar to that of the buffer solution, the
sample’s density is usually increased by mixing it with a loading dye enabling the sample to be
suspended in the wells of the gel. - The gel enables us to see the migration of the protein across the gel upon applying an electric
current. - The protein migrates from the cathode end (negative) to the anode end (positive) of the gel,
enabling the protein to migrate along the gel in the same direction.
How does SDS-PAGE work? (5)
- A solid medium in the form of a gel is submerged in a buffer solution.
- The gel has wells on top in which a protein sample can be transferred using a pipette.
- Because the density of the protein sample is typically similar to that of the buffer solution, the
sample’s density is usually increased by mixing it with a loading dye enabling the sample to be
suspended in the wells of the gel. - The gel enables us to see the migration of the protein across the gel upon applying an electric
current. - The protein migrates from the cathode end (negative) to the anode end (positive) of the gel,
enabling the protein to migrate along the gel in the same direction.
What is SDS? (3)
- SDS (Sodium Dodecyl Sulphate) is an amphipathic detergent with an anionic tail and a lipophilic tail.
- SDS is used to denature and dissociate proteins from each other and confers a negative charge on
the protein, masking the protein’s intrinsic charge. - SDS-treated proteins have similar mass to charge ratios and shapes.
What happens during PAGE? (2)
- During PAGE (Polyacrylamide Gel Electrophoresis), the rate of protein migration is determined by molecular weight, where all protein migrates from the cathode to the anode.
- PAGE is the support medium, and the gel has pores which are determined by the concentration of the acrylamide used to prepare it. A lower concentration of acrylamide will mean larger pores and vice versa.
PAGE:
- In a gel with uniform density, the relative migration distance of protein (Rf) is ______
_______ to the log of its mass. - Performing a gel with proteins of known and unknown molecular masses simultaneously allows one to estimate the masses of the unknown proteins by plotting the relationship between ___ and the log of its mass.
Negatively Proportional
Rf
What is 2D-Gel Electrophoresis? (3)
- The aim of 2D-Gel Electrophoresis to analyse complex protein mixtures from cells, tissues and other biological samples.
- 2D-Gel Electrophoresis is a combination of Isoelectric Focusing (explained on next page) and SDS- PAGE (explained above).
- This is done by separating and identifying proteins in two steps or two dimensions.
2D-Gel Electrophoresis
What are the steps involved? (2)
Step 1 – Isoelectric focusing (IEF):
Proteins are separated according to their isoelectric points (the pH at which a particular molecule carries no net electrical charge).
Step 2 – SDS-PAGE
Proteins are separated according to their mass.
2D-Gel Electrophoresis
What are the steps involved? (2)
Step 1 – Isoelectric focusing (IEF):
Proteins are separated according to their isoelectric points (the pH at which a particular molecule carries no net electrical charge).
Step 2 – SDS-PAGE
Proteins are separated according to their mass.
What is Isoelectric Focusing (IEF)? (8)
- Isoelectric focusing is used for the analysis of complex protein mixtures from cells.
- A solution with proteins of various molecular masses and different charges are separated according
to their isoelectric points, where upon the application of an electric current through the gel matrix,
the protein becomes stationary at the point where its net charge is 0. - A pH gradient is applied onto a gel and an electric current is applied across the gel, making one end
more positive than the other. - Proteins are charged at all pH values besides their isoelectric values (the pH at which a particular
molecule carries no net electric charge). - Proteins migrate along the gel until they reach their isoelectric points, where they remain
stationary. - Positively charged proteins are pulled towards the negative end of the gel and vice versa.
- The pH gradient in the gel is formed by the presence of ampholytes, which are complex mixtures of
synthetic polyamino-polycarboxylic acids. - In Isoelectric focusing, proteins are separated because of their charge rather than their molecular
mass.
What is Protein Purification: Chromatography?
- Proteins must be purified to ensure that the highest purity of protein is obtained.
- Pure protein does not have additional cell components, or other protein and/or contaminants that can contribute to the efficient functionality of the protein of interest.
- Chromatography is a fundamental component of most, if not all, recombinant protein purification.
- There are many types of chromatography, but the basic principle is the same. A sample containing the desired protein is applied to a solid matrix and allowed to elute (remove an adsorbed substance by washing with a solvent) through a porous plug where the eluate (a solution obtained by elution) can be collected.
- Over time, the sample is applied to the matrix, and various fractions of the sample can be collected, based on the type of chromatography used for the purification.
What is Protein Purification: Chromatography?
- Proteins must be purified to ensure that the highest purity of protein is obtained.
- Pure protein does not have additional cell components, or other protein and/or contaminants that can contribute to the efficient functionality of the protein of interest.
- Chromatography is a fundamental component of most, if not all, recombinant protein purification.
- There are many types of chromatography, but the basic principle is the same. A sample containing the desired protein is applied to a solid matrix and allowed to elute (remove an adsorbed substance by washing with a solvent) through a porous plug where the eluate (a solution obtained by elution) can be collected.
- Over time, the sample is applied to the matrix, and various fractions of the sample can be collected, based on the type of chromatography used for the purification.
There are 3 main types of chromatography, based on the protein that is the basis of the purification: (3)
1) Affinity-Based Chromatography
2) Size-Exclusion Chromatography
3) Ion-Exchange Chromatography
What is 1) Affinity-Based Chromatography?
The solid matrix, which is usually composed of beads, is coated with a molecule which has an affinity for the protein.
For example, the beads maybe coated with an antigen that has a high affinity to the protein, therefore causing the protein to bind to the beads, and not be eluted with the rest of the sample. The protein can then be collected using a relevant solvent that breaks the bond between the antigen and the protein of interest, and the protein fragment can be collected.
What is 1) Affinity-Based Chromatography?
The solid matrix, which is usually composed of beads, is coated with a molecule which has an affinity for the protein.
For example, the beads maybe coated with an antigen that has a high affinity to the protein, therefore causing the protein to bind to the beads, and not be eluted with the rest of the sample. The protein can then be collected using a relevant solvent that breaks the bond between the antigen and the protein of interest, and the protein fragment can be collected.
What is 2) Size-Exclusion Chromatography?
The solid matrix traps the protein within pores in the solid matrix. Chromatography beads with specific pore sizes can be purchased to enable entrapment of the protein (of known size) of interest.
What is 3) Ion-Exchange Chromatography?
Ion-exchange chromatography facilitates binding of the protein of interest to the solid matrix based on opposing charges.
For example, in the image alongside, the solid matrix composed of beads is positively charged and binds the negatively charged protein molecules.
Pure Protein:
- In lane 2 in the image below, an _____-______ protein (pure protein) is shown, whereas lane 1 shows the banding pattern for the total protein lysate, prior to purification.
- Once a protein has been purified, there are many ways in which it may be utilised, as shown below.
affinity-purified
What is the Recombinant DNA (rDNA)?
Recombinant DNA (rDNA) is a DNA strand that is formed by 2 or more DNA sequences which are often from different organisms. The resulting Recombinant DNA is put into a host cell where it is expressed into a new protein, called a Recombinant Protein (rProtein).
What is the Recombinant DNA (rDNA)?
Recombinant DNA (rDNA) is a DNA strand that is formed by 2 or more DNA sequences which are often from different organisms. The resulting Recombinant DNA is put into a host cell where it is expressed into a new protein, called a Recombinant Protein (rProtein).