Indirectly, since RAM does not process the frames, but the processor which does, usually needs something from the RAM. The processor might work at 100% capacity but if you suddenly need to get in new textures or something the processor has to wait for the RAM to finish the loading before it can continue processing the frames. Your FPS goes lower only because the game is loading/"paused", not because you have insufficient processing power.
CPU/GPU Performance - RAM Performance = Total Performance (Assuming CPU/GPU Performance > RAM Performance)
Using my crappy example again, if I take longer to get your your coffee I am
directly affecting the time you take in getting your coffee. The same can be said here: If the RAM is slow, the CPU/GPU's performance are lowered by that amount.
Another example: You (the CPU) can sign a total of 50 contracts per minute, but if I (the RAM) only bring 10 contracts to you per minute you can only sign 10 in the end. I am
directly affecting your performance.
This can also work the other way: You (the CPU) can sign a total of 50 contracts per minute, but if I (the RAM) bring 2000 contracts to you per minute you can only sign 50 in the end. In this case you are
directly affecting my performance.