Question

Describe the 4 levels of structure of a protein and describe how the R groups influence these structures.

Answer 1

The four levels of protein structure are identified by the degree of complexity in the polypeptide chain.

a) Primary Structure describes the order in which amino acids are joined together. Proteins are formed from a set of 20 amino acids. Amino acids contain R group, hydrogen atom, carboxyl group, and amino group. The "R" group varies among amino acids and determines the differences between these protein monomers.

b) Secondary Structure describes the folding of a polypeptide chain in 3-D shape. The folding will be of two types. First type is the alpha (α) helix structure in which protein forms coiled spring and is secured by hydrogen bonding. Second type is the beta (β) pleated sheet. In this type, polypeptide bond is folded or pleated and is held together by hydrogen bonds. The hydrogen bonds affects the folding or plating of the structures.

c) Tertiary Structure refers to the 3-D structure of a protein. The R group of the amino acid is either hydrophobic or hydrophilic. These interactions contribute to the folding and shaping of a protein. The amino acids with hydrophilic R groups seek contact with aqueous environment, while amino acids with hydrophobic R groups will avoid contact with water. Folding also affects covalent bond between the R groups of cysteine amino acids.

d) Quaternary Structure refers to the structure of a protein resulting from the interaction between multiple polypeptide chains. Proteins with quaternary structure may consist of more than one of the same type of protein subunit. Each subunit will have different R group and leads to different structures.