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Question
Host cells are treated with chemical agents to increase their competency for taking in recombinant DNA during the production of transgenic organisms. Why is this step necessary?
Host cells are treated with chemical agents to increase their competency for taking in recombinant DNA during the production of transgenic organisms. Why is this step necessary?
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Solution
The correct option is C DNA is a hydrophilic molecule and is unable to pass through the hydrophobic lipid bilayer of host cell membrane.
Competency refers to the ability of a cell to take up foreign DNA from its environment. Cells are unable to readily take up DNA from their environment, unless they are treated with chemical agents to make them competent.
This is because DNA is a hydrophilic molecule and hence cannot readily pass through the cell membrane, which is hydrophobic in nature.
The cell membrane is composed of a bilayer of phospholipids. The hydrophilic heads of the phospholipids are arranged on either side and interact with the external environment.
Whereas, the hydrophobic tails are arranged towards the inner side, to protect them from the surrounding environment. Thus the DNA molecule finds it difficult to pass through the hydrophobic lipid bilayer of host cell membrane.
Thus to make the host cells readily uptake the DNA, the cells are made competent by the addition of chemical agents like CaCl2, MgCl2,etc. These salts dissociate to release divalent cations (Mg2+, Ca2+, etc) which attract the negative charges on the DNA phosphate backbone and the phosphate heads of the phospholipids. This allows the DNA to bind to the phospholipid bilayer.
DNA is a highly stable nucleic acid and hence there are no chances of disintegration of the DNA molecule during entry through the cell membrane.
The vector DNA chosen to carry the gene of interest is usually a small sized molecule. Hence the recombinant DNA molecule itself is also small in size. This is preferred because large molecules tend to break down during the isolation and purification of the recombinant vector DNA from the host cell.
Large vector DNA would also pose problems during the manipulations required for inserting the gene of interest into the vector DNA. Thus the size of the recombinant DNA does not hinder its uptake by the host cells.
The host cells have no receptors on their membranes for binding to the DNA molecule. But this does not interfere with the uptake of DNA. Once the cell is made competent, it can easily take in DNA.
Competency refers to the ability of a cell to take up foreign DNA from its environment. Cells are unable to readily take up DNA from their environment, unless they are treated with chemical agents to make them competent.
This is because DNA is a hydrophilic molecule and hence cannot readily pass through the cell membrane, which is hydrophobic in nature.
The cell membrane is composed of a bilayer of phospholipids. The hydrophilic heads of the phospholipids are arranged on either side and interact with the external environment.
Whereas, the hydrophobic tails are arranged towards the inner side, to protect them from the surrounding environment. Thus the DNA molecule finds it difficult to pass through the hydrophobic lipid bilayer of host cell membrane.
Thus to make the host cells readily uptake the DNA, the cells are made competent by the addition of chemical agents like CaCl2, MgCl2,etc. These salts dissociate to release divalent cations (Mg2+, Ca2+, etc) which attract the negative charges on the DNA phosphate backbone and the phosphate heads of the phospholipids. This allows the DNA to bind to the phospholipid bilayer.
DNA is a highly stable nucleic acid and hence there are no chances of disintegration of the DNA molecule during entry through the cell membrane.
The vector DNA chosen to carry the gene of interest is usually a small sized molecule. Hence the recombinant DNA molecule itself is also small in size. This is preferred because large molecules tend to break down during the isolation and purification of the recombinant vector DNA from the host cell.
Large vector DNA would also pose problems during the manipulations required for inserting the gene of interest into the vector DNA. Thus the size of the recombinant DNA does not hinder its uptake by the host cells.
The host cells have no receptors on their membranes for binding to the DNA molecule. But this does not interfere with the uptake of DNA. Once the cell is made competent, it can easily take in DNA.
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