Question

Compare and contrast the primary, secondary, tertiary and quaternary structures of Myoglobin(Mb) and Hemoglobin(Hb). You can create a Venn diagram or do columns listing the similarities and differences.  BE SPECIFIC

Answer 1

Answer:

Let us first see what are Hemoglobin and Myoglobin:

Hemoglobin (Hb) is the protein contained in red blood cells which is responsible for delivery of oxygen to the tissues. Hemoglobin is responsible for red color of blood. It is composed of four protein chains, two alpha chains and two beta chains, each with a ring-like heme group containing an iron atom.

Myoglobin is a monomeric heme protein found mainly in muscle tissue where it serves as an intracellular storage site for oxygen. During periods of oxygen deprivation oxymyoglobin releases its bound oxygen which is then used for metabolic purposes.

Both Hemoglobin and Myoglobins are proteins. Lets us understand what are the structures of proteins and how these proteins are classified into primary, secondary, tertiary and Quaternary.

As we know that, proteins are made of amino acids, each protein has definitive structure due to their composition. Each amino acid is comprised of an amino group, a carbon, a carboxylic acid group and an R- group. The hydrophobic or hydrophilic nature of amino acid is determined by this R group.

Primary structure:

When amino acids join together, they form a peptide bond and make a polypeptide structure. This occurs via a condensation reaction, resulting in a water molecule. Once amino acids make a polypeptide structure in a specific order, this sequence makes up a primary protein structure.

Secondary structure:

However, these polypeptides do not remain in a straight line, but rather they bend and fold to form a three-dimensional shape that can either look like a spiral (an alpha helix) or a sort of accordion shape. These polypeptide structures make up a secondary protein structure. These are held together via hydrogen bonds.

Tertiary structure:

Tertiary protein structure is a final form of a functional protein comprised of its secondary structure components. The tertiary structure will have specific orders to its amino acids, alpha helices and beta-pleated sheets, all of which will be folded into the stable tertiary structure.

Quaternary structure:

While all proteins possess these three structures, some consist of multiple amino acid chains. This type of protein structure is called quaternary structure, making a protein of multiple chains with various molecular interactions. This yields a protein complex.

Comparison of primary, secondary, tertiary and quaternary structures of Hemoglobin and Myoglobin

Comparison

The below table shows the comparison of different forms of Hemoglobin and Myoglobin

Primary structures of Hemoglobin and Myoglobin
Hemoglobin	Myoglobin
141 (α-chain) and 146 (β-chain) amino acids	153 amino acids
Secondary structures of Hemoglobin and Myoglobin
Hemoglobin	Myoglobin
8 α –helixes for each α-chain and β-chain	8 α-helixes
Tertiary structures of Hemoglobin and Myoglobin
Hemoglobin	Myoglobin
Folding of α helixes	Folding of α helixes
Quaternary structures of Hemoglobin and Myoglobin
Hemoglobin	Myoglobin
Tetramer of two identical α β- dimers	None (monomer)
Similarities irrespective different structures
oxygen-binding globular protein	oxygen-binding globular protein
contain the oxygen-binding haem as their prosthetic group.	contain the oxygen-binding haem as their prosthetic group.
give the red color to the blood and muscles respectively.	give the red color to the blood and muscles respectively.

Differences between Hemoglobin and Myoglobin

Hemoglobin	Myoglobin
Red protein responsible for transporting oxygen in blood	Red protein with haem which carries and stores oxygen in muscle cells
Molecular weight 64 kDa	Molecular weight 16.7 kDa
Composed of 4 polypeptide chains	Composed of single polypeptide chains
Binds with four oxygen molecules	Binds with single oxygen molecule
Low affinity for oxygen	High affinity for oxygen
Found in blood stream	Found in muscles

Summary: Though these two are proteins in nature, they share few common feaures and several important diffferences.