Chemistry 9701 · AS & A Level · Nitrogen compounds

Nitrogen compounds — practice question

Electrophoresis can be used to separate a mixture of amino acids. The diagram shows a typical practical arrangement.
(a)[2]

After the power supply is switched on, some amino acids may not travel and remain stationary. Suggest an explanation for this observation.

(b)[1]

The amino acid glycine has the formula $\text{H}_2\text{NCH}_2\text{CO}_2\text{H}$. Identify the species present on the filter paper if glycine moves to the left (positive) end of the filter paper.

(c)[3]

A different electrophoresis gave the result below. What can be deduced about the relative sizes and charges of amino acid species A, B and C?

(d(i))[3]

After a partial hydrolysis, these tripeptides were obtained from a particular polypeptide: ala-gly-asp, gly-ala-gly, lys-val-ser, ser-ala-gly, val-ser-ala. Since the N-terminal amino acid is lysine (lys), suggest the amino acid sequence of the shortest polypeptide that could produce the tripeptides above.

(d(ii))[1]

Which tripeptide in (i) has the lowest $M_r$?

(d(iii))

Select one amino acid from those listed in the table that has an ionic side-chain at $\text{pH } 8$.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Amino acid is a zwitterion / overall uncharged

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