Question

1. Contrast the structure and function of myoglobin and hemoglobin. Describe the primary, secondary, tertiary and quaternary structure of both proteins. Describe their motifs and domains if appropriate.

2. How similar are the mammalian hemoglobin and myoglobin (in terms of amino acid composition)?

3. Recall the functions and structure of leghemoglobins, chlorocruorins, hemerythrin and hemocyanin. In what organisms are those proteins found? How are this globins different from mammalian globins?

4. Not all O₂ molecules bind to each of the four subunits of hemoglobin with the same affinity. Explain why.

Answer 1

1) Ans. Myoglobin is a globular protein, contains a single polypeptide chain of 153 amino acids residues and a single heme group.about 75% of the polypeptide chain is alpha helical the iron atom of the heme protein is directly bonded to a nitrogen atom of a histidine side chain of globin.myoglobin function as a oxygen storage Protein,binds with oxygen molecule.

Hemoglobin is an oligomeric, allosteric, conjugated protein with four polypeptide chain joined by non covalent bond.it contain 2 Alpha and 2 beta chain.it functions as a Oxygen transport,caron dioxide transport.it has an important role as a buffer.

Functional difference between myoglobin and hemoglobin-

Hemoglobin is an allosteric protein,where as myoglobin is not.

The shape of the Oxygen dissociation curve of hemoglobin is sigmoidal,where as that of myoglobin is rectangular hyperbolic i.e.myogloin has higher affinity for oxygen that does hemoglobin.

The affinity of oxygen depends on ph,and for myoglobin is independent of ph