Answer:
Secondary level of protein structure
Explanation:
The proteins are formed of the monomer units called amino acids which bond with each other via peptide bond and form a linear peptide structure called the primary level structure of the protein.
The proteins to perform several functions in a cell undergoes structural conformation and attain the helical form called alpha helix due to the involvement of alpha carbon in bond formation and a pleated sheet called beta-pleated sheet due to the involvement of beta carbon. These structures are known as a secondary level of protein structure.
Thus, a Secondary level of protein structure is the correct answer.
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