The Student Room Group

Which of these are true??

1) The primary structure of a protein refers to the predominant three-dimensional structures in which it occurs.

2) Adult haemoglobin contains two copies of two different polypeptides.

3) A protein with a net positive charge in solution at pH 7 tends to lose that charge as the pH of the solution is decreased.

4) A peptide bond involves a covalent link between a carbon atom of one amino acid and a nitrogen atom of another amino acid.
Hey,

Using process of elimination, I think number 3 is true. This is because the primary structure of a protein only refers to the sequence of amino acids in a polypeptide chain; I am pretty sure that there is no such thing as an adult haemoglobin and an infant haemoglobin and lastly, a peptide bond is formed when a water molecule is removed, so the bond would be CON.

I hope that helps! :smile:
I disagree,

During condensation, the -OH is removed from the carboxyl group and the -H is removed from the amino group - so it would be C-N covalent linkage.

Number 4 is true.

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As for number 3,

Proteins are positive at pHs below their Isoelectric points (pI) due to higher protonation. Therefore, this proteins pI is higher than pH7. Lowering the pH will increase the concentration of protons and can therefore only protonate more residues on the protein (make it more positive).

So the net positive charge WOULD NOT decrease.

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