Amino Acids are biological molecules that form the underlying structure of proteins, and as such are vital to life. By combining to form proteins, as well as acting as catalysts to break down Carbon Dioxide or urea, amino acids help the body in its day-to-day operation.
Since amino acids fold themselves to attach to other structures and to form proteins, they can take many different shapes depending on their final form. In folding to form proteins and then to function, the amino acids may change its shape a number of times. Most will form a donut shape during its folding to keep hydrophobic side chains away from water, which would interfere with the fold. After these side chains are inside the donut, the folding continues until the amino acid is in its most energy-efficient shape.
Essentially, almost all amino acids can fold into a donut shape in the right circumstances. Most folding depends on the situation and how the amino acid is reacting with its environment. Amino acids will always fold to protect certain parts and to form together with other enzymes and proteins. While not all amino acids fold the same way, many fold in similar ways to gain the same result.