A biopolymer is a polymer found in nature. Starch, proteins and peptides, and DNA and RNA are all examples of biopolymers, in which the monomer units, respectively, are sugars, amino acids, and nucleic acids. The exact chemical composition and the sequence in which these units are arranged is called the polymer's primary structure. Many biopolymers spontaneously "fold" into characteristic shapes, which determine their biological functions and depend in a complicated way on their primary structures. Structural biology is the study of the shapes of biopolymers.
The convention for a protein is to list its constituent amino acid residues as they occur from the amino terminus to the carboxylic acid terminus. The convention for a nucleic acid sequence is to list the nucleotides as they occur from the 5' end to the 3' end of the polymer chain, where 5' and 3' refer to the numbering of carbons around the ribose ring which participate in forming the phosphate diester linkages of the chain. Such a sequence is called the primary structure of the biopolymer.
There are a number of biophysical techniques for determining sequence information. Protein sequence can be determined by Edman degradation, in which the N-terminal residues are hydrolyzed from the chain one at a time, derivatized, and then identified. Mass spectrometer techniques can also be used. Nucleic acid sequence can be determined using gel electrophoresis and capillary electrophoresis.