Protein sequence

Proteins are made of sequences of amino acids which condense into complex polymers, forming peptide bonds between the amine and carboxylic acid groups of separate amino acids, and shedding a water. The leftover group is called an amino acid residue, sometimes informally just called a “residue.” Note that residues can be grouped into various loose categories based on the chemical group (“sidechain”) which is coming off the the core “backbone” (N, C\(\alpha\), C=O). The degree of hydrophilicity of these sidechain groups is critical. In the salt water environment of the cell, entropic and enthalpic interactions drive the overall chain to fold such that hydrophobic groups get buried and hydrophilic groups get exposed. By convention, we think of the sequence as being oriented from the amine-terminal (N-term) to the carbonyl-terminal (C-term) end, since is also how the protein is synthesized in the ribosome.

By TungstenEinsteinium - Own work, CC BY-SA 4.0, Link