Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/2
K:G
['gGGA GAGA gGGA A>G E2 gGGA GABG', 'g2 defa (b/a/g) (a/g/f) (d/e/f) gB A>G']  
X:1
L:1/8
M:2/2
K:G
 gGGA GAGA | gGGA A>G E2 | gGGA GABG | AA/A/ (b/a/g) e2 g2 || defa (b/a/g) (a/g/f) | 
 (d/e/f) gB A>G E2 | dega (b/a/g) ab | d/d/d b/a/g e2 g2 :|  