Question

two basic types of protein secondary structures are α -helix and β -sheet. the alpha helix is a right - handed coil. the beta sheet can form in between two or more segments of the polypeptide chain lying side by side. the entire folded protein 3d structure is known as the tertiary structure.
the main two secondary structures of proteins are alpha helix and beta sheet which are represented respectively by which two letters in the image?
a) a and c
b) b and c
c) b and a

Explanation:

In protein secondary - structure representation, alpha - helix is often represented by a coiled structure and beta - sheet by a flat, extended structure. Without seeing the actual image, but based on common representation, if one of the letters represents a coiled structure (alpha - helix) and another represents a flat structure (beta - sheet).

Answer:

Since no image is provided for reference, we cannot accurately choose from the given options. But if we assume standard representations, we need to identify the coiled (alpha - helix) and flat (beta - sheet) structures in the image. If we had to guess without the image, we would need more context. However, if we follow the general convention where the coiled structure is one of the options and the flat structure is the other, we would need to visually inspect the image. Since we don't have it, we note the lack of necessary information.