Secondary Structure of Proteins and the Alpha-Helix

The alpha-helix belongs to the SECONDARY structure. The primary structure is only the straight line of amino acids in order. When some parts of that thread coil like a revolving staircase, that coiled shape is the secondary structure. This exact line was asked in NEET 2026, so learn it word for word: alpha-helix = secondary structure.

Only RIGHT-HANDED helices are observed in proteins. NCERT states this clearly. NTA loves to change one word to 'left-handed' to trap you. If the option says left-handed helix, it is wrong for proteins.

Primary structure = the sequence, the order of amino acids from the N-terminal (first) to the C-terminal (last) end, drawn as a straight line. Secondary structure = when parts of that line fold into a helix (revolving staircase shape). So primary is the ORDER; secondary is the local COILING.

No. NCERT says 'only some portions of the protein thread are arranged in the form of a helix.' Other regions fold into other shapes. So the alpha-helix is present only in parts, not the entire chain.

Hydrogen bonds hold the coil in place. These are weak bonds, but many of them together give the helix a stable, regular spiral shape. This is why secondary structure is a repeating, ordered pattern.

It is the local coiling of the protein thread into a helix, like a revolving staircase, held by hydrogen bonds.

NCERT states only right-handed helices are observed in proteins. For NEET, treat this as a direct fact; left-handed is the trap option.

No. Alpha-helix is a protein secondary structure made of amino acids. The DNA double helix is two nucleotide strands. Do not mix them in NEET options.

The hydrogen bond. Many weak hydrogen bonds together keep the spiral shape stable and regular.

The tertiary structure, where the whole chain folds into a 3-D hollow shape, then quaternary when many subunits join (like haemoglobin).