Question

The alpha-helix and beta-pleated sheet structures of a protein are associated with its:

• A. quaternary structure
• B. primary structure
• C. secondary structure
• D. tertiary structure

Hint:

The secondary structure of proteins includes alpha-helices and beta-pleated sheets, which are stabilized by hydrogen bonds between backbone atoms.

Answer 1

The Correct Option is C

The question tests your understanding of protein structure. Proteins have different levels of structural organization, and understanding these is crucial for many competitive exams: 

• Primary structure: This is the linear sequence of amino acids in a protein chain. It is the most basic level of protein structure.
• Secondary structure: This includes regular patterns of folding within a protein. The two most common secondary structures are the alpha-helix and the beta-pleated sheet. These structures are stabilized by hydrogen bonds between the backbone atoms in the polypeptide chain. 
  Example: The alpha-helix is a right-handed coiled structure, whereas beta-pleated sheets consist of two or more segments of polypeptide lying side by side, with hydrogen bonds forming between them.
• Tertiary structure: This is the overall three-dimensional shape of a single protein molecule resulting from interactions among various side chains (R groups) of the amino acids.
• Quaternary structure: This level of structure arises when a protein consists of more than one polypeptide chain, and these chains interact with each other.

The question asks about alpha-helix and beta-pleated sheet structures, which, as described, are part of the secondary structure of proteins. Hence, the correct answer is secondary structure.

Answer 2

The alpha-helix and beta-pleated sheet are types of secondary structures in proteins. These structures arise from the folding of the polypeptide chain due to hydrogen bonding between the backbone atoms. The primary structure is the linear sequence of amino acids, while the tertiary structure refers to the overall three-dimensional shape of the protein. The quaternary structure refers to the arrangement of multiple polypeptide chains. Thus, the correct answer is secondary structure.