How do we measure the catalytic efficiency of enzymes found inside our cells and inside our body? This will be the focus of this lecture. So let's begin by taking a look at the following graph. This is the same graph we focused on many times in previous lectures. And so on this graph, the x axis is a substrate concentration and the y axis is the velocity, is the rate at which the enzyme actually operates on that specific substrate. And what the blue curve describes is how the rate, the velocity of that enzyme changes as we increase the substrate concentration in the environment.