Preheat oven to 350°F Lightly butter and flour 13 x 9 x 2-inch metal baking pan. In medium bowl, combine flour, baking soda, baking powder and salt. Using electric mixer, beat butter and 1 1/2 cups sugar in large bowl until blended. Add eggs and beat until fluffy. Mix in 3/4 cup sour cream, bananas and lemon juice. Add dry ingredients to banana mixture and beat until well blended. Transfer batter to prepared pan.
Bake cake until top is golden and tester inserted into center comes out clean, about 30 minutes. Cool completely on rack. (Can be prepared 2 weeks ahead. Cover cake and freeze. Thaw before continuing.).
Beat remaining 1/2 cup sour cream, powdered sugar and cream cheese in large bowl until well blended. Spread frosting over cooled cake.