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MCAT

Unit 3: Lesson 1

Chemical and physical sciences practice passage questions

Understanding the ballistics of gene bombardment

Problem

Gene gun bombardment is a method of inserting foreign genetic material into a host cell. In this procedure, a viable host cell is repeatedly shot with spherical gold nanoparticles that have been coated with plasmid DNA. While the collision damages many host cells, a few successfully survive and incorporate the DNA into their genome.
In a typical gene gun, a plate containing a fixed weight of coated gold nanoparticles faces a plate containing many samples of the host cell type. A screen is positioned between the two objects. During bombardment, the plate and gold particles are rapidly accelerated using an explosive charge, which transfers a fixed quantity of energy, E, to the plate and particles over a very short time interval. The plate then collides with the screen, which stops the plate immediately but which allows the gold nanoparticles to continue towards the sample at the impact velocity. Upon reaching the sample, the gold nanoparticles are ballistically scattered as they collide with various tissues and structures, making the final location of the nanoparticles inherently random. Figure 1 shows the basic setup of a gene gun.
Figure 1. A: An explosive charge drives the plate bearing the nanoparticles towards the screen. B: The screen stops the plate, but the nanoparticles pass through. C: The nanoparticles enter the sample and scatter.
Over the entire time interval from when the explosion ends to when the gold particles strike the tissue, which of the following quantities is the smallest?
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