What is the Difference Between Alpha Helix and Beta Pleated Sheet?

The alpha helix and beta pleated sheet are both types of secondary structures found in proteins, but they have distinct differences in their conformation and hydrogen bonding patterns:

1. Conformation: The alpha helix has a right-handed coiled rod-like structure, while the beta pleated sheet has an extended conformation, i.e., linear or sheet-like structure.
2. Hydrogen Bonding: In the alpha helix, intramolecular hydrogen bonding forms within the polypeptide chain to create a spiral structure. In the beta pleated sheet, beta sheets are formed by linking two or more beta strands by intermolecular hydrogen bonds.
3. Amino Acid Residues: In an alpha helix, 3.6 amino acid residues are wound to form a polypeptide. In a beta-strand, three to ten amino acids are combined to create a polypeptide.
4. R Groups: The R groups of the amino acids stick outward from the alpha helix, where they are free to interact. In the beta pleated sheet, the R groups extend above and below the plane of the sheet.
5. Strand Orientation: The chains or beta strands in a beta sheet can run parallel (all N terminals on one end) or anti-parallel (chains run in opposite direction, with N terminal and C terminal ends alternate).
6. Dimensions: An average alpha-helix is 10 residues long and generally ranges between 4 to 40 residues in length. A beta-strand is typically 3 to 10 amino acids long.
7. Preferred Amino Acids: Amino acids such as alanine, glutamate, leucine, and methionine are often found in alpha helices, while amino acids like tryptophan, tyrosine, and phenylalanine are often found in beta pleated sheets.
8. Occurrence: Both alpha helices and beta pleated sheets are found in many globular and fibrous proteins.

In summary, the main differences between alpha helices and beta pleated sheets lie in their conformations, hydrogen bonding patterns, amino acid residue arrangements, and preferred amino acids.

Comparative Table: Alpha Helix vs Beta Pleated Sheet

Alpha helix and beta pleated sheet are two types of secondary structures found in proteins. Here is a table highlighting their differences:

Both structures are held together by hydrogen bonds, which form between carbonyl and amino groups of the backbone. The R groups of the amino acids extend above and below the plane of the sheet in the beta pleated sheet structure.