Preheat oven to 450° F. Grease a baking sheet; set aside.
In a large mixing bowl sift together flour, sugar, baking powder, baking soda and salt. Cut in shortening to resemble small peas; set aside.
Dissolve yeast in warm water - 105°-115° F ). Add yeast and buttermilk to flour mixture and mix with a fork to make a soft dough. Knead briefly.
Roll dough out on a floured surface and cut out 24 circles with a biscuit cutter. Place on baking sheet and bake until puffed and golden, about 10 minutes.Makes 24 biscuits