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by alyx 957 days ago
How do you "enter a cell" without exerting energy?
5 comments

cells are not dead lumps, they are living things driven by energy (food sugar), doing stuff all the time and reacting to their environment (even if their environment is inside your body).

The surface of the cell, the cell membrane, is a wall that has little "doors" or "windows" that will open and close to let stuff IN (sugar to burn for example, and raw protein parts (amino acids) so they can make them into useful proteins, and they open the windows to let stuff OUT, waste products, the useful proteins they just made, CO2. There's another membrane doing a similar thing around the nucleus within the cell.

The windows in these walls open and close automatically controlled a bit like a lock with magnets in it. If a "key" with the right combination of magnets is inserted in the lock, the lock magnets will align to open the window.

Viruses carry keys that know how to get in your windows, pretending to be authorized but it's a forgery. The virus doesn't "do" anything, it doesn't know its not doing anything, it just hangs around till it fits a lock. Viruses that look like good keys get into the reproduction system and reproduce. Viruses that don't unlock anything don't.

if your tea leaves have these viruses in them, adding water to the tea will spread the viruses around the same way the tea spreads, and they will come into contact with your tongue cells.

Diffusion is typically passive, sometimes (rarely) guided. But actual genome delivery usually requires energy stored in the capsid. For membraneous viruses, it's usually energy stored in the spike/fusion protein, plus some help from the host.

Note: I'm talking about energy stored in the 3D structure, not ATP molecules.

Where does the energy stored in the 3D structure come from? How does it get infused with said energy?
When the virus is made by the previous cell, as the virus is assembled, it is assembled into what is called a "metastable" state. This is a low, but not lowest energy state, or energy well. Typically the lowest possible energy state requires some additional input of energy to reach (it has to get over a small hump to find the deepest well). That energy often comes from an interaction with a new host.
It's the same way chemicals have effects even though they have no energy/way to move themselves etc: they just diffuse in whatever medium they're in (like salt diffusing in water). No energy needed
You convince the cell to bring you in.

Or you "store" energy when you are built - sars-cov-2 is built with a coiled spring which is triggered by a cell receptor when it binds. This coiled spring releases mechanical energy to force merging between virus and cell wall:

https://www.youtube.com/watch?v=e2Qi-hAXdJo

The viral capsid, or the spike proteins/binding proteins, are in a metastable state. Upon interaction with the host/target, they use that energy to rearrange into a lower energy state. Genome delivery is usually associated with that state.
When you move your body you shuffle stuff around. Blood also flows.

There's also wind.