More atomic force microscopy videos. These show Cas9 "searching" through DNA and then cutting it. It's surprising how long the DNA cut takes. It'd be cool to see similar videos for bridge recombinases. These were published by the great @hnisimasu in 2017.

About 6.2 billion basepairs of DNA are 'packed' into the nucleus of each human cell. Scaled by a factor of 500,000x, this is akin to packing a 1,000-kilometer-long string (roughly the distance from New York City to Detroit) into a small bedroom. How does all that DNA fit? Well, let’s do some back-of-the-envelope calculations: The human genome is 6.2 billion basepairs in length, and each basepair is separated by 0.34 nanometers along the helix. (A carbon-carbon single bond is about half that length.) Multiply these numbers together, and we see that the DNA inside of each cell stretches about 2.1 meters in length. This is not a scaled value! A human cell nucleus has a diameter of about 6 micrometers. So what fraction of that nucleus is 'occupied' by the DNA? First, we calculate the volume of the cell nucleus. Given a radius of 3 micrometers, and using the regular equation (V = 4/3*pi*r^3), we get a volume of 113 cubic micrometers. The DNA can be modeled as a cylinder. This cylinder is 2.1 meters long and about 2 nanometers in diameter. Again, using the equation for volume of a cylinder (V=π*r^2*h) we get 6.6 cubic micrometers. In short: The human genome occupies about 6% of the cell nucleus. This is not tightly packed at all. The main problem is that once you pack all of this 'string' into the nucleus, you have created a really difficult search problem for yourself. This string is coiled up tightly and, if you are an enzyme, then you might need to find a particular segment of the string located at, say, position 4,284,283,192. Good luck with that! And yet, cells have evolved highly effective search strategies to quickly retrieve information, which I think is one of the great innovations of evolution.