Final answer:
The longest dimension of a coiled B-sheet with 40 amino residue and 4 turn residue is 21.6 Å.
Step-by-step explanation:
The longest dimension of a coiled B-sheet can be calculated by multiplying the distance between each turn of the coil (5.4 Å) by the number of turns. In this case, there are 4 turns. So, the longest dimension of the coiled B-sheet can be calculated as:
Longest dimension = Distance between each turn × Number of turns = 5.4 Å × 4 = 21.6 Å