What is the longest amino acid?
Titin
Titin
Titin is the third most abundant protein in muscle (after myosin and actin), and an adult human contains approximately 0.5kg of titin.[8]  With its length of ~27,000 to ~33,000 amino acids (depending on the splice isoform), titin is the largest known protein.[9]   Furthermore, the gene for titin contains the largest number of exons (363) discovered in any single gene,[10] as well as the longest single exon (17,106 bp).