Complete the analogy

Haemoglobin : Quaternary structure :: Myoglobin : ________

Solution:

Haemoglobin is a complex protein composed of four polypeptide chains (two alpha and two beta subunits), which associate to form a quaternary structure. Myoglobin, on the other hand, is a simpler protein consisting of a single polypeptide chain. Its functional three-dimensional arrangement is its tertiary structure. Therefore, the analogy is completed by 'Tertiary structure'.