Question

question 28
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which of the following structures of a protein is defined by hydrogen bonds between amino acids in different regions of the original polypeptide strand creating alpha - helices or beta - pleated sheets?
tertiary structure
quaternary structure
primary structure
secondary structure

Explanation:

• Primary structure: It is just the linear sequence of amino acids in a polypeptide chain, held together by peptide bonds. There is no folding or formation of helices/sheets at this level.
• Secondary structure: This level of protein structure is characterized by hydrogen - bonds. Hydrogen bonds form between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid in the polypeptide chain. These hydrogen bonds lead to the formation of common secondary structures like alpha - helices (a coiled structure) and beta - pleated sheets (a more extended, sheet - like structure).
• Tertiary structure: It is the overall three - dimensional folding of a single polypeptide chain. It involves interactions such as hydrophobic interactions, disulfide bonds (in addition to hydrogen bonds which also play a role but are not the defining feature for the formation of helices/sheets at this level), and van der Waals forces. The alpha - helices and beta - pleated sheets (formed at the secondary level) are further folded at the tertiary level.
• Quaternary structure: This structure is relevant when a protein is composed of multiple polypeptide chains (subunits). The interactions between these different polypeptide chains (such as hydrogen bonds, ionic bonds, and hydrophobic interactions) define the quaternary structure.

Answer:

Secondary structure