Answer:
Side chain
Explanation:
Amino-acids differ from each other because of thier SIDE CHAINS.
The side chain confers to amino-acids their unique physical and chemical properties, thereby determining their structure and function.
The side chain called the R group and represented with letter R.
For example serine and threonine have polar side chains and this makes them soluble in water.
conclusion, amino-acids are different from each other because of their SIDE CHAINS.
