A chemotaxis assay is being developed to understand how cells migrates in respon

Question

A chemotaxis assay is being developed to understand how cells migrates in response to chemical signals like growth factors. A thin channel is created between two giant reservoirs by bonding a piece of silicon rubber with a rectangular groove running its length to the surface of a glass slide. To conduct assay, the cells are placed in the very middle of the 1-mm long channel (cross section: 200 m x30 m) and allowed to attach to the surface overnight. Then, different growth factors are added to the reservoirs to create diffusion gradients from one channel to the next, and the cell behavior is observed to see which direction they will move, and how fast.

For this problem, you are worried about the fate of the cells in the middle of the channel overnight—will they have enough oxygen? How many cells can safely live in the center if the oxygen consumption rate is 1.4 x10-16 mol/(cell-s) and you do not want the oxygen concentration to drop below 25 mmHg (millimeter of mercury) ?

You can assume that the cells occupy an infinitely thin plan in the middle of the channel. Also assume the diffusion coefficient of oxygen in the culture medium is 2.3x10-5 cm2 /sec. The dish is placed in a standard humidified incubator at 370C and 5% CO2 and the medium outside the channel is well mixed.

Explanation / Answer

Chemotaxis assay is the movement of an organism in response to the chemical stimulus. A thin channel is created between two giant reservoirs by bonding a piece of silicon rubber with a rectangular groove running its length to the surface of a glass slide. To conduct assay, the cells are placed in the very middle of the 1-mm long channel (cross section: 200 mm x30 mm) and allowed to attach to the surface overnight. Then, different growth factors are added to the reservoirs to create diffusion gradients from one channel to the next, and the cell behavior is observed to see which direction they will move, and how fast.

Yes, they (bacteria) has enough oxygen for its survival because the diffusion coefficient of oxygen in the culture medium is 2.3X10-5cm2/sec. Most of the cells occupy an infinitely thin plan in the middle of the channel hence, the number of cells living safely would be dependent on oxygen consumption rate.

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