The structure of a peptide is given below: If the absolute values of the net charge of the peptide at pH =2, pH =6 , and pH =11 are z 1 , z 2 , and z 3 , respectively, then what is z 1 + z 2 + z 3 ?

Chemistry · Biomolecules

JEE Advanced 2020 — Paper 2 — Question 21

The structure of a peptide is given below:

If the absolute values of the net charge of the peptide at $\mathrm{pH}=2, \mathrm{pH}=6$ , and $\mathrm{pH}=11$ are $\left|\mathrm{z}_{1}\right|,\left|\mathrm{z}_{2}\right|$ , and $\left|\mathrm{z}_{3}\right|$ , respectively, then what is $\left|\mathrm{z}_{1}\right|+\left|\mathrm{z}_{2}\right|+\left|\mathrm{z}_{3}\right|$ ?

Answer: 5

Numerical answer — enter this value.

Step-by-step solution

At $\mathrm{pH}=2$ (highly acidic), the structure of the peptide will be as shown below.

So, $\left|\mathrm{Z}_{1}\right|=2$

At $\mathrm{pH}=6$ it will exist as neutral or zwitter-ion structure as shown below

So, according to this condition, $\left|\mathrm{Z}_{2}\right|=0$

At $\mathrm{pH}=11$ (highly basic), the given peptide will exist as:

So, $\left|Z_{3}\right|=|-3|=3$

$\left|Z_{1}\right|+\left|Z_{2}\right|+\left|Z_{3}\right|=2+0+3=5$

Answer key and solution verified before publishing.

Practise Biomolecules

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Solve a similar one free

Exam: JEE Advanced 2020
Paper: Paper 2
Subject: Chemistry
Chapter: Biomolecules
Topic: proteins