<Tr> <Td_colspan="2"> Infobox references </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> </Tr> <P> Valine (symbol Val or V) is an α - amino acid that is used in the biosynthesis of proteins . It contains an α - amino group (which is in the protonated − NH form under biological conditions), an α - carboxylic acid group (which is in the deprotonated − COO form under biological conditions), and a side chain isopropyl group, making it a non-polar aliphatic amino acid . It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet . Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, beans and legumes . In the genetic code it is encoded by all codons starting with GU, namely GUU, GUC, GUA, and GUG . </P> <P> Like leucine and isoleucine, valine is a branched - chain amino acid . In sickle - cell disease, a single glutamic acid in β - globin is replaced with valine . Because valine is hydrophobic, whereas glutamic acid is hydrophilic, this change makes the hemoglobin prone to abnormal aggregation . </P>

The side chain for valine is classified as a