Secondary structure

Definition

Secondary structure refers to the local folded structures that form within a polypeptide chain due to interactions between the backbone atoms in the amino acid sequence. These structures are primarily stabilized by hydrogen bonds and can manifest as alpha helices and beta sheets, both of which are crucial for the overall stability and functionality of proteins derived from peptides.

5 Must Know Facts For Your Next Test

1. Secondary structure is primarily stabilized by hydrogen bonding between the carbonyl oxygen and the amide hydrogen of amino acids in the polypeptide chain.
2. Alpha helices typically have 3.6 amino acids per turn and are a common feature in fibrous proteins like keratin.
3. Beta sheets can be parallel or antiparallel, depending on the orientation of the strands, influencing their stability and properties.
4. The presence of secondary structures can significantly affect the physical properties and biological functions of proteins, including enzymatic activity and binding interactions.
5. Disruptions in secondary structure can lead to misfolding of proteins, which is implicated in various diseases, including Alzheimer's and prion diseases.

Review Questions

• How do secondary structures like alpha helices and beta sheets contribute to the overall stability of a protein?
  • Secondary structures such as alpha helices and beta sheets provide critical stability to proteins through hydrogen bonding within the polypeptide backbone. These local structures allow for a compact arrangement that reduces the energetic cost associated with maintaining an extended polypeptide chain. The formation of these structures sets the stage for higher-order folding into tertiary and quaternary structures, which are essential for proper protein function.
• Compare and contrast alpha helices and beta sheets in terms of their structural characteristics and stability factors.
  • Alpha helices are characterized by a right-handed coil where each turn consists of approximately 3.6 amino acids, stabilized by hydrogen bonds between residues four apart in the sequence. In contrast, beta sheets consist of strands aligned alongside each other, connected through hydrogen bonds that can be either parallel or antiparallel. While both provide structural integrity to proteins, alpha helices tend to be more flexible while beta sheets often contribute to rigidity due to their extensive hydrogen bonding patterns.
• Evaluate how disturbances in secondary structure formation can lead to protein misfolding and disease states.
  • Disturbances in the formation of secondary structures can significantly impact protein folding pathways, leading to misfolding. Misfolded proteins often lose their functional conformation, which can result in aggregation or dysfunctional interactions with other biomolecules. Such misfolded states are associated with several neurodegenerative diseases, including Alzheimer’s disease, where beta-amyloid plaques form due to improper folding and aggregation of peptide fragments, highlighting the importance of secondary structure integrity in maintaining cellular health.

Related terms

Alpha Helix: A common structural motif in proteins where the polypeptide backbone coils into a right-handed spiral, with hydrogen bonds forming between every fourth amino acid.

Beta Sheet: A secondary structure consisting of beta strands connected laterally by at least two or three backbone hydrogen bonds, forming a sheet-like appearance.

Tertiary Structure: The overall three-dimensional shape of a protein formed by the folding of the polypeptide chain, which is influenced by interactions between side chains of the amino acids.