Protein Structure: From Primary Sequence to Quaternary Complexity

Protein Structure
Primary Structure: The primary structure is the sequence of amino acids joined by peptide bonds. These radicals are arranged alternately on either side.
Secondary Structure:
-Alpha-helix Structure: This is a structural complication of the primary structure, resembling a helix. The links that rotate the structure are non-peptidic. It was formed in two phases:
1. There is a shift from one plane to another, similar to a door opening, approximately 100 degrees.
2. There is a 180-degree rotation around an axis located in the central part of the plane. This movement leaves the plane in an inverted position, higher than the anterior plane.
These two movements are simultaneous, and their repetition forms a double alpha-helix. All oxygen atoms are oriented in the same direction, and hydrogen atoms in the opposite direction. This allows for the formation of hydrogen bonds between them, providing stability to the molecule.
-Beta or Folded Sheet Structure: Amino acids form a widespread prop reminiscent of a zig-zag. Initially, there are no hydrogen bonds between them. Stability is achieved when various segments of the same chain associate through hydrogen bonds.
Collagen Helix: Collagen has a high number of glycine, proline, and hydroxyproline residues, which prevent the formation of the alpha-helix structure. The stability of this structure is achieved when three helices form a superhelix.
Tertiary Structure: This describes the three-dimensional arrangement of the secondary structure elements in space.
-Filamentous Forming: These structures maintain their shape and are only slightly twisted. They are insoluble in water.
-Globular Forming: This is more complicated, as proteins fold into a nearly spherical shape. They are soluble in water. In this type of conformation, straight sections with alpha-helices and bends with beta-pleated sheets can be observed. The various stretches are held together by hydrogen bonds or Van der Waals forces.
Quaternary Structure: This represents the maximum degree of structural complexity, providing information about the weak links between several peptide chains. Each chain is called a protomer.