Which of the following describes amino acids?

Amino acids are indeed the building blocks of proteins, making the provided answer correct. Proteins are vital macromolecules that perform a myriad of functions in the body, including serving as enzymes, hormones, structural components, and antibodies. There are 20 different amino acids that combine in various sequences to form proteins, with some being classified as essential because the body cannot synthesize them and must obtain them from dietary sources.

In contrast, the other options involve different types of biological molecules and processes, which do not accurately describe amino acids. Fatty acids are components of lipids, not amino acids. Carbohydrates, while important for energy, are made up of sugars and not directly constructed from amino acids. Lastly, while the liver does play a central role in energy metabolism, it doesn't produce amino acids as energy; instead, it processes nutrients from the diet, including amino acids, into various forms that the body can use for energy or other functions. Thus, the description of amino acids as building blocks of protein is precise and foundational to understanding their role in nutrition and physiology.