If you have not already done so, download Avogadro for free and watch the tutorials if necessary.
Encephalins are brain peptides with opiate activity. An encephalin molecule is described by Try-Gly-Gly-Phe-Leu amino acid sequence.
Open Avogadro and then build the encephaline molecule by writing the sequence given (sequence Build → Insert → Peptide).
After optimizing and rotating the structure properly, open a new page of Avogadro and import the leucine molecule. Compare the two molecules: can you identify the position of the leucine in the encephalin?