One possible form of a protein
One protein can have several different isoforms. During the translation process different exons can be used for the final protein, this process is called: alternative splicing. Some proteins are found in both a membrane-bound and a free form that resides in the cytoplasm. The second isoform lacks the exon that codes for a transmembrane segment. Isoforms of proteins can also be encoded by two different genes in your DNA or caused by single nucleotide polymorphisms in one of the alleles for that protein.