A word before we start: this lecture has changed a lot since the YouTube videos were recorded, so treat the playlist as background and not as a transcript of today.
Lecture title slide: In vitro Assays. A link to the course YouTube playlist for this lecture.
A two-step process
Purify the component of interest (destroys the cells)
Observe the activity, structure, or abundance of the purified fractions
Everything in this lecture is some version of these two steps. First you purify the thing you care about, and that destroys the cells — which is why these are called in vitro assays. Then you look at what you purified: its activity, its structure, or just how much of it there is. The first half of today is the purifying and the second half is the looking.
Every in vitro assay is two steps. First, purify the component of interest, which destroys the cells. Second, observe the activity, structure, or abundance of the purified fractions.