Q.In the process for the biolistics which metal is used for the coating?
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Direct (Physical) Methods of Gene Transfer
Agrobacterium tumefaciens is nature's own genetic engineer for plants -- but not every plant cell is a willing host, and not every organism has a natural vector at all. For these cases, biotechnologists bypass biological vectors entirely and deliver DNA by purely physical or mechanical means.
The Main Physical Methods
- Micro-injection -- DNA is injected directly into the nucleus (or cytoplasm) of an individual cell using an extremely fine glass micropipette, under a microscope. This is precise but can only be done cell-by-cell, so it doesn't scale to large populations of plant cells the way other methods do.
- Gene gun (biolistics / particle bombardment) -- the workhorse method for plants, especially cereals and other species Agrobacterium struggles to infect. Microscopic particles of an inert metal (gold or tungsten) are coated with the DNA to be delivered, then physically fired at high velocity into plant cells or tissue using a device that resembles a small gun. The particles carry the DNA straight through the cell wall and membrane, and once inside, the DNA can be released and expressed or even integrated into the host genome. Because it doesn't depend on a biological infection process, the gene gun works across a very wide range of plant species and cell types.
- Disarmed pathogen vectors -- if a plant virus or bacterium other than Agrobacterium naturally infects a species Agrobacterium doesn't, it can sometimes be "disarmed" (stripped of its disease-causing genes while keeping its infection machinery) and used as an alternative vector.
Why "Direct" Matters …
The biolistics (gene gun) method delivers DNA into plant cells with tough cell walls by physically firing DNA-coated particles into the tissue, and the metal chosen for this needs to be dense and chemically inert. …
The biolistics or 'gene gun' method delivers DNA into plant cells by physically shooting DNA-coated metal micro-particles - typically tungsten or gold - into the tissue at high velocity.
Biolistics (particle bombardment) is used mainly to introduce recombinant DNA into plant cells (especially those with tough cell walls, where Agrobacterium-mediated transformation is less effective). Micro-particles of a heavy, inert metal - tungsten o …
- CBSE 2025Set X11 markMCQQ.In which method the plant cells are bombarded with high velocity microparticles of gold coated with DNA?(a) Microinjection(b) Biolistics(c) Heat shock(d) Cloning
›Reveal solutionSolution
Bombarding plant cells with high-velocity gold/tungsten microparticles coated with DNA is the biolistics (gene gun) method.
Biolistics, also called the gene gun method, introduces alien DNA into cells (especially plant cells) by bombarding them with high-velocity microparticles of gold or tungsten coated with DNA. Microinjection directly injects DNA into a cell/nucleus using a fine needle, heat shock is used to …
- CBSE 2025Set ANNUAL1 markQ.Name any two methods of vectorless gene transfer.
›Reveal solutionSolution
Vectorless (direct) gene transfer methods introduce foreign DNA into a cell without using a biological vector such as a plasmid or virus; common examples include the gene gun and micro-injection.
In the gene gun (biolistic/particle bombardment) method, DNA is coated onto tiny gold or tungsten particles, which are then physically shot into plant cells/tissue at high velocity, allowing the DNA to enter the cell and, in some cases, integrate into the genome - this method is especially useful for plant cells with rigid cell walls.
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- CBSE 2025Set ANNUAL1 markQ.Name the method in which the alien DNA is directly injected into the nucleus of an animal cell.
›Reveal solutionSolution
Micro-injection is the technique in which recombinant/alien DNA is directly injected into the nucleus of an animal cell (or into a fertilised egg/embryo) using a fine glass micropipette under a microscope.
Bacterial cells can take up foreign DNA on their own once made 'competent' (e.g. by CaCl2 treatment and heat shock), but this approach does not work for most animal cells because of their more complex membrane systems and low natural transformation efficiency. Several methods have therefore been developed to introduce alien DNA into other kinds of host cells:
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- CBSE 2024Set E1 markMCQQ.Which of the following methods is used to inject recombinant DNA into nucleus of animal cell directly?(a) Transfection(b) Transformation(c) Gene gun(d) Microinjection
›Reveal solutionSolution
Microinjection injects recombinant DNA straight into the nucleus of an animal cell using a fine glass needle.
Several methods deliver foreign DNA into host cells. In animal cells, recombinant DNA can be injected directly into the nucleus using an extremely fine needle — this is called microinjection. The gene gun (biolistics) method, in contrast, is used for plant cells, where cells are bombarded with high-velocity micro-particles …
- CBSE 2020Set 57/3/11 markMCQQ.Introduction of an alien DNA into a plant host cell is achieved by making them (A) Competent with bivalent ions (B) Using microinjections (C) Using gene gun (D) Using lysozymes and chitinase
›Reveal solutionSolution
The question asks which method is used to introduce alien DNA into a plant host cell. The correct answer is the gene gun (option C), because plant cells have a tough cell wall that blocks direct entry, and the gene gun physically shoots DNA-coated particles through it.
Concept and Intuition
The core challenge here is the plant cell wall. Unlike animal cells, which have only a flexible plasma membrane, plant cells are surrounded by a rigid wall made of cellulose, hemicellulose, and pectin. This wall is a formidable physical barrier.
So, when we want to introduce foreign DNA into a plant cell, we cannot simply use the same tricks that work for bacteria or animal cells. We need a method that either:
- Bypasses the wall entirely (e.g., by removing it first), or
- Punches through it physically.
The gene gun (also called a biolistic particle delivery system) does exactly the latter. It fires microscopic gold or tungsten particles coated with DNA at high velocity into the plant tissue. The particles penetrate the cell wall and membrane, delivering the DNA directly inside.
Let's see why the other options fail for plant cells specifically.
Step-by-Step Breakdown
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Option (A): Competent with bivalent ions
This is the standard method for making bacterial cells (like E. coli) take up plasmid DNA. Treating them with cold calcium chloride (CaCl₂) and a heat shock makes their membranes permeable.
Why it fails for plants: Plant cell walls are too thick and rigid for this chemical treatment to work. Even if the membrane becomes permeable, the DNA cannot physically reach it through the wall.
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Option (B): Using microinjections
This works beautifully for animal cells (e.g., injecting DNA into a fertilized egg or a cultured cell). A fine glass needle directly delivers DNA into the nucleus or cytoplasm.
Why it fails for plants: The plant cell wall is too tough for a glass needle to penetrate without shattering the tip or crushing the cell. Also, plant cells are often part of a tissue, making individual microinjection impractical and inefficient.
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Option (C): Using gene gun — This is correct. …
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