Q.Describe the primary and secondary structures of a protein, explaining how each arises and giving one example of a protein exhibiting a well-defined secondary structure.

[!TLDR]

Primary structure is the linear amino-acid sequence joined by peptide bonds; secondary structure is local folding (alpha-helix, beta-pleated sheet) from backbone hydrogen bonding -- keratin shows a strong alpha-helical secondary structure.

[!ANSWER]

Primary structure = amino-acid sequence via peptide bonds; secondary structure = alpha-helix/beta-sheet via backbone H-bonds, e.g. keratin (alpha-helix).

The primary structure of a protein is simply the linear order in which its amino acids are joined, one after another, by peptide bonds along the polypeptide backbone, running from the free N-terminal end to the free C-terminal end; this sequence is unique to each protein and is specified directly by the genetic code. The secondary structure arises when hydrogen bonds form between the backbone -NH and C=O groups of amino acids that lie near one another along the chain, producing regular, repeating local folding patterns -- the two most common being the alpha-helix, a right-handed coil, and the beta-pleated sheet, in which extended strands lie side by side. Keratin, the fibrous protein of hair and nails, is built extensively around the alpha-helix, giving it its characteristic strength and elasticity.

[!ANSWER]

Primary structure = amino-acid sequence via peptide bonds; secondary structure = alpha-helix/beta-sheet via backbone H-bonds, e.g. keratin (alpha-helix).

Define each level in terms of the specific bond/interaction responsible (peptide bonds for primary; backbone hydrogen bonds for secondary), then cite one named example.

Describing secondary structure using side-chain (R group) interactions -- those belong to tertiary structure; secondary structure is specifically about backbone hydrogen bonding.