What Is A Secondary Structure
Definition
Secondary structure of a protein
The secondary structure of a protein refers to the regular, repeating patterns that form when a polypeptide chain folds. These patterns arise from interactions between the amino acids in the backbone of the protein.
- Proteins start as simple linear chains of amino acids, known as polypeptides.
- Due to interactions between the atoms in the polypeptide backbone, the chain folds into specific, stable patterns.
- These patterns are stabilized by hydrogen bonds between atoms in the backbone.
Hydrogen bonds form between the carbonyl group (C=O) of one amino acid and the amine group (N-H) of another.
Two Main Types of Secondary Structure
The Alpha Helix: A Coiled Spring
The alpha helix is a right-handed coil, like a spring.
- How it works:
- The polypeptide backbone coils into a spiral.
- Hydrogen bonds form between the C=O of one amino acid and the N-H of the amino acid four residues ahead in the sequence.
- These bonds run parallel to the axis of the helix.
- Key Features
- Compact and Stable: Hydrogen bonds hold the helix tightly together.
- R-Groups Project Outward: Side chains extend from the helix, allowing interactions with the environment or other molecules.
- Versatility: Found in many proteins, including enzymes and structural proteins like keratin in hair.
- Hemoglobin, the protein that carries oxygen in your blood, contains alpha helices.
- These helices help form the compact, globular shape of the molecule, which is essential for binding oxygen efficiently.
To identify an alpha helix in a protein structure, look for a coiled pattern with hydrogen bonds running parallel to the coil’s axis.
The Beta-Pleated Sheet: A Folded Landscape
The beta-pleated sheet is a sheet-like structure formed by aligned polypeptide strands.
