last one The side groups are what make each amino acid different from the others. Of the 20 side groups used to make proteins, there are two main groups: polar and non-polar. These names refer to the way the side groups, sometimes called "R" groups, interact with the environment.
The answer that makes most sense to me is D. We stopped needing to kill whales, yay! :P
Your answer is <span>3.
Iron</span>
