Here is a link that talks a little bit about how it is made:
The description of how insulin is made is pretty technical, and I don't have enough of an understanding of the process to go into it here, but I encourage you to check out the article. To summarize, though, what it basically says is that synthetic insulin is made using DNA that scientists alter in the lab to turn it into what they want. Pretty amazing, isn't it?
Synthetic insulin has been a blessing for diabetics. First of all, animal insulin could cause some allergic reactions -- the danger of getting sick was probably part of why people would take as little insulin as possible, and restrict their diet to suit it. In addition, I suspect animal insulin was a little more variable in how long it took to work and what effect it had.
Synthetic insulin, on the other hand, has given scientists the opportunity to program the way the insulin behaves. The result is a variety of different insulins that work very differently. Diabetics can use short-acting insulin when they eat or to correct a high blood sugar, and take long-acting insulin to control their blood sugar levels the rest of the time.
It did surprise me to read that synthetic insulin was first developed in 1978. I had no idea it was so long ago! Think how far we've come since then -- when you consider how much more difficult it was to control diabetes 20 or 30 years ago, I am thankful that I was diagnosed during a time when medical technology was so advanced!