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Biochemistry

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Amino Acids, Proteins and Porphyrins

Question
30 out of 107
 

When the following amino acids are separated by running them on agarose gel, at pH 7, which one of them will migrate slowest to the anodic end



A Glycine
B Valine

C Aspartic acid
D Lysine

Ans. D Lysine

1. At iso-electric pH (pI) Amino acid bear no charge ie. zero charge ie. zwitterionIc structure ie.

+ve and —ve charge is equal.

2. Towards more acidic side of pI i.e. more H+ concentration the amino acid accept H+ and become more positively charged

At pI

Zwitter ion form

Towards more alkaline side i.e less H+, the amino acid become more negatively charged

At less than pI

At isoelectric pH (pI)

At more than pI

For Aspartic acid

1.

At pH<1 bear net charge +ve

at PI ie. pH 3 = zero charge

At pH 6 – 8 bear net charge = -1

For Lysine

2.

At less < 9.7 PI bear net charge = +ve

At isoelectric pH (pI), i.e 9.7, net charge = 0

At> 9.7 pI bear net charge = -ve

For Glycine

pI=(pk1+pk2)/2

= (2.4+9.8)/2

= 6.1

3.

At less 6.1 pI bear net charge = +ve

Glycine at pI 6.1 bear net charge = 0

At>6.1 pI bear net charge = - ve

For valine

pI = (2.2 + 9.9)/2

= 12.1/2 = 6

4.

At pI< 6 bear net charge = + ve

At pI 6 = zero charge

At pI>6 bear net charge = - ve

Now it clears from above that at pH-7 as given in Q. [Q SGPGI 04] Aspartic acid at physiological pH (7.4) bears negative charge (as explained).

1. Aspartic acid bears = - ve charge 2. Lysine bears = + ve charge

3. Glycine bears = -ve charge 4. Valinebears = - ve charge

High voltage Electrophoresis: Net charges depends on pH of the medium. When current is applied molecules with a net negative charge, migrated toward the anode (+ve pole) and those with a net positive charge toward the cathode (-ve pole).

So, lysine bear net +ve charge at pH-7, it moves very slowly towards to anode (+ve pole), due to

force of repulsion

Amino Acids, Proteins and Porphyrins Flashcard List

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