A protein's secondary structure arises due to interactions between amino acids. Two common secondary structures found in many proteins are alpha helices and beta sheets. Classify the following statements as pertaining to alpha helices or beta sheets. 1. Keep their shape due to hydrogen bonds between adjacent polypeptides chains
2. form long thin structures important for transmembrane proteins
3. flat zig zag like structure
4. a rigid spring like structure around a central axis

Alpha helixes:

- form long thin structures important for transmembrane proteins

- have a rigid spring like structure around a central axis

Beta sheets:

- Keep their shape due to hydrogen bonds between adjacent polypeptides chains

- have a flat  zig zag like structure

Explanation:

Alpha helices and beta pleated sheets are two types of secondary structure found in proteins.

Alpha helix: In this structure, the polypeptide backbone is tightly wound around an imaginary central axis drawn longitudinally through the center with the R groups of the amino acids protruding outward from the helical backbone. This structure looks like a spring and could either be a left-handed or right-handed helix, though the left-handed helix has not been observed in proteins. Each turn of the helix includes about 3.6 amino acid residues.

The alpha helix is stabilized by a hydrogen bond between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the amino-terminal side of that peptide bond.

Alpha-helices due to their structure, are the most common transmembrane proteins- protein structure element that crosses biological membranes.

Beta sheets: In the beta conformation, the backbone of the polypeptide chain is extended into a zigzag structure. The zigzag polypeptide chain can be arranged side by side to form a structure resembling a series of pleats known as beta sheets. Hydrogen bonds formed between adjacent segments of the polypeptide chain functions to stabilize the structure.

The beta comformation in the form of turns is common in globular proteins.

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