Structure and Function of Haemoglobin

Primary structure: This is hemoglobin at the simplest level, it is made up of chains of amino acids, in which peptide bonds separating each amino acid. It consists of four polypeptide chains, two alpha (?) chains, and two betas (?) chains.

Secondary Structure: The two types of secondary structure found in proteins are the alpha-helix (?) or the Beta-pleated (?) sheet. These structures both involve polypeptide chains, however, in this instance they form different shapes, these are held together by weak intermolecular forces called hydrogen bonds. Hydrogen bonds can be found between the N-H and C=O groups, giving it a more stable structure.

Tertiary Structure: This is the main bonding which is involved in stabilizing the structure in each hemoglobin chain. The haem molecule is involved in the bending of the hemoglobin, creating the 3D structure of the chain. Hemoglobin is a globular protein, this means that ball-like structures are formed, where the hydrophobic part is towards the center and the hydrophilic part is towards the edges, this means that they are water soluble.

Quaternary Structure: These are proteins that contain more than one polypeptide chain which is held together by hydrogen, ionic and disulfide bonds. Hemoglobin has four polypeptide chains, and all of these contain a haem group. Also, there is an iron ion (Fe²?) this is where the oxygen binds due to iron’s high affinity for oxygen. Hemoglobin can be found in the red blood cells in the circulatory system.

How The Protein is Able to Maintain its Structure: Hydrophobic Interaction – These weak bonds are found inside of the 3D structure of hemoglobin, and they form between R groups, which only contain hydrogen and carbon. These interactions are hydrophobic, meaning they repel water. These amino acids contain non-polar side chains, meaning they’re not charged. Hydrophilic Interaction – These are found on the outside of the 3D structure of hemoglobin. They are hydrophilic, this means that they attract water. These amino acids contain polar side chains, meaning they are charged. Overall, this means that hemoglobin is soluble in water. Disulfide Bridges – These are formed between two sulfur atoms found on two opposite cysteine amino acids when this happens, each one loses a H?. These are exceptionally strong bonds and can only be broken by reducing agents, not by things like pH temperature.    Hydrogen Bonds – These can form between an oxygen or a nitrogen atom and a hydrogen atom found on different amino acids. For this to occur, the oxygen or nitrogen must have a lone pair of electrons in order to form a hydrogen bond. Then, a pair of electrons will be shared by the nitrogen or the oxygen atom on one amino acid and the hydrogen atom on the amino acid. Ionic Bonds – These are formed between oppositely charged variable (R) groups which contain a carboxylic acid (-COOH) and an amine (-NH2) group. These bonds are stronger than hydrogen bonds, however, they can be broken by a change in temperature or pH.

The function of Haemoglobin: Haemoglobin is found in the red blood cells, where it carried oxygen through the respiratory system and around the rest of the body. It is a globular protein which shows a quaternary structure, and it also contains other structures such as haem groups and iron ions. This allows oxygen to bind to it, and this is possible because the iron ion gives hemoglobin a high affinity for oxygen.