The four pyrole rings in hemoglobin molecule are joined together by?

Ans. B. Methylene bridges. (Ref. Harper's Biochemistry 26th / pg. 270-278)# The four pyrrole rings of protophyrin IX are held together by methylene bridges.Structure of Hb# Hb = Heme + globulin (2? + 2? chains)Q# The iron is in Fe++ state in the heme of functional Hb.# Iron can form six "Co-Ordinated Bonds".# Iron is held at the centre of the heme by 4 nitrogen of porphyrin rings (pyrrole rings).# Iron bind internally (by 5th linkage) with amino acids of Histidine.Q# The co-ordinated position of Fe++ is a available to bind to O2.# The four Pyrole rings are joined by Methylene or Methylidene bridge (-C = bridge).# Hb-intemally contains mostly Hydrophobic amino acids (forming "Heme pocket") and Hydrophilic amino acids on their surfaces.# The "Heme pocket" of a-subunit are adequate for entry of O2 while b-subunits Heme pockets blocks entry of O2 by a valine residues.