Mechanical Linear Amplifier

What it shows:

One falling domino knocks down two, which in turn knock down three, etc. Use it to model cascade signaling.

How it works:

Twenty five rows of dominoes are set up in front of the first domino. Each successive row is comprised of one additional domino, e.g. the 2nd row has two, the 3rd row three, ... the 25th row has twenty five. A total of 325 dominoes get knocked down in a couple of seconds after the 1st one falls.

The action can be contrasted to a second board which has 11 rows of 30 tiles each, for a total of 330 dominoes. It takes about 20 seconds to topple all of them over, one row at a time.

Setting it up:

A dedicated plywood board has the rows drawn on it. The best place for the board is atop one of the large heavy blue carts (a light cart moves too easily and may prematurely trigger the event while setting it up). A steady hand and patience is required. Allow yourself about 20 minutes to set up each of the two boards.

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The demonstration stemmed from a request by Prof Robert Lue and Prof Susan Mango (Dept of Molecular & Cellular Biology) to model exponential amplification in some mechanical manner. Although not exponential amplification by any means, the falling dominoes can be used to model biological cascade signaling through MAPKKK. MAP (Mitrogen-Activated Protein) kinases are involved in a pathway through which information is sent from the outside of the cell to the nucleus. Protein kinases are enzymes that transfer phosphate and phoshorylation, in turn, alters the chemical properties of neighbors — the phosphorylated receptor recruits other signaling proteins (adaptor proteins) which relay the signal to the cytoplasm and eventually into the nucleus. The MAP kinase pathway is composed of three consectutive kinasses, MAPKKK. A signal coming from outside initiates the cascade of kinases which integrates multiple signals from different extracellular inputs. With such a big transcription factor effect, the original signal gets amplified exponentially thus providing a lot of sensitivity. On the other hand, sometimes such sensitivity is not desirable and a linear response is more appropriate. The board with 11 rows of tiles that are toppled one at a time models that response.