9/3/03
25
Aggregation Stage
| A chemical called acrasin |
|
| Chemotaxis to cAMP (cyclic
Adenosine Monophosphate) pulses |
|
| Move toward increasing cAMP
concentrations |
|
| Release more of it
themselves |
|
| Rings typically appear
first, then spirals |
|
| 10 000 - 50 000 may be more
typical; S&G say 10 000 - 100 000 |
|
| The problem: |
|
| Signal goes out to gather, but where? There is no prearranged place. |
|
| This is a symmetry-breaking situation. |
|
| There are many equally good centers, but must agree on
one (or a few) |
|
| One of the many important roles played by randomness |
|
| Amplification of random fluctuation |
|
| (Dicty. homepage, ZI-Munich;
Slime Molds, Encarta) |