Biology · Biomolecules · NEET
The FIRST amino acid is the N-terminal. NCERT states: the left end of the protein line is the first amino acid, and this first amino acid is the N-terminal amino acid. The last amino acid on the right end is the C-terminal. So the order is N-terminal (start) to C-terminal (end).
Primary structure is the positional information in a protein, meaning the exact sequence of amino acids: which amino acid is first, which is second, and so on. It is just the ORDER of amino acids in the linear chain, not the folding. Proteins are heteropolymers, so this sequence can use different amino acids.
NCERT imagines a protein as a straight line. The LEFT end is the first amino acid = N-terminal. The RIGHT end is the last amino acid = C-terminal. Do not confuse this with a polysaccharide chain, where the RIGHT end is the reducing end and the LEFT end is the non-reducing end.
Because it decides everything else. The order of amino acids in the primary structure determines how the protein folds into secondary, tertiary, and quaternary structures, which fixes its function. NEET often gives a statement that swaps N-terminal and C-terminal to trick you, so remember first = N-terminal.
No. N-terminal and C-terminal are for PROTEINS (amino acid chains). Reducing and non-reducing ends are for POLYSACCHARIDES (sugar chains). NCERT keeps them separate: proteins use N/C ends, sugars use reducing/non-reducing ends. Mixing them up is a common NEET trap.
Statement I: A protein is imagined as a line, the left end represented by first amino acid (C-terminal) and the right end represented by last amino acid (N-terminal). Statement II: Adult human haemoglobin consists of 4 subunits (two subunits of alpha type and two subunits of beta type). In the light of the above statements, choose the correct answer:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the sequence (positional order) of amino acids in the polypeptide chain, that is, which amino acid is first, second, third, and so on.
The first amino acid is the N-terminal. The last amino acid is the C-terminal.
N-terminal marks the end of the chain carrying the first amino acid (the amino/N end). It is drawn on the left side of the protein line in NCERT.
The C-terminal end carries the last amino acid of the chain and is drawn on the right side of the protein line.
Primary structure is only the linear sequence of amino acids. Secondary structure is when parts of that thread fold into a helix (only right-handed helices in proteins).
