Going backwards in time, would we expect mutations to erase or accumulate. Going backwards in time is not like making a film of a cell going forwards and then watching it play backwards, at least from my knowledge. The only difference would be that entropy would decrease rather than increase. I put this under chemistry because entropy and energetics is much more like chemistry than biology. Could cells even operate, ie function, when entropy was reversed?
Right after polymerization, a new DNA double helix is hemimethylated. This is when proofreading takes place. Going backwards in time the dam methylase wouldn't be able to distinguish which strand was unmethylated, and if there was a mistake on the new Double Helix then it would have a 50% chance of being incorporated into the old double helix. So for every mutation that takes place it would have a 50% chance of being incorporated into old DNA. ... . furthermore, since the dam methylase acts to methylate unmethylated strands it might just de-methylate both strands if that is energetically favorable; although i would guess a hemimethylated Double Helix has lower entropy than a non-methylated Double Helix and so would be preferable when entropy is going in reverse.
I will ignore the issue of what the effects of time-travel would be like on entropy etc. But if you suddenly reversed the entropy changes of all the cell's chemical reactions, many of them would not longer work properly - they would go at different rates, or even reverse. The entropy change in a reaction is a big part of determining the reaction's change in Gibbs free energy, which determines the equilibrium of a reaction. So, yeah...tinker too much with the entropy change of your cell's reactions, and you probably just die right away.
Yes, this is exactly the issue- could cells survive if entropy was decreasing rather than increasing. I'm not sure if time travel would necessarily do this, but it would seem so to me. Astronauts don't die when time speed up in orbit. So, time dilation in itself might not affect Gibbs free energy. However, if order was the more favorable configuration than disorder, chemistry would be different. Wouldn't all reactions go backwards? Would a person start projecting photons from the photoreceptors in their eyes?
Some would go backwards, others would have their equilibrium shifted even further in the direction they already go. If you have a reaction that decreases entropy and is spontaneous, then changing the laws of physics so that decreased entropy was favorable would make it even more spontaneous. The magnitude of the entropy change's effect on the chemical equilibrium will depend on temperature too, so you have to take that into account; at low temperatures the entropy change matters less.
