Problem Title: Isoelectric Point and Electrophoresis #1: The isoelectric point,

Question

Problem Title: Isoelectric Point and Electrophoresis

#1: The isoelectric point, pI, of the protein deoxyribonuclease I is 10.2 , while that of ribonuclease T1 is 2.9 .

What is the net charge of deoxyribonuclease I at pH 7.3 ?_________(Chose: positive or negative)
What is the net charge of ribonuclease T1 at pH 1.5 ?_________(Chose: positive or negative)

The isoelectric point of cysteine is 5.07 ; phenylalanine , 5.48 .

During paper electrophoresis at pH 4.3 , toward which electrode does cysteine migrate? _________ (Chose: positive or negative)
During paper electrophoresis at pH 4.5 , toward which electrode does phenylalanine migrate? _________ (Chose: positive or negative)

_________________

#2: The isoelectric point, pI, of the protein papain is 9.6 , while that of lipase B is 5 .

What is the net charge of papain at pH 5.1 ?_________ (Chose: positive or negative)
What is the net charge of lipase B at pH 7.3 ?_________ (Chose: positive or negative)

The isoelectric point of asparagine is 5.41 ; glycine , 5.97 .

During paper electrophoresis at pH 6.5 , toward which electrode does asparagine migrate? _________ (Chose: positive or negative)
During paper electrophoresis at pH 7.1 , toward which electrode does glycine migrate? _________ (Chose: positive or negative)

Explanation / Answer

Iso electric point is the pH at which molecules have a net zero charge and they exist as zwitter ions.

At any pH less than pI, the molecule has a net positive charge and at pH more than pI it will have a net negative charge.

pI of deoxyribonuclease is 10.2. so net charge on deoxyribonuclease I at pH 7.3 is POSITIVE.

pI of ribonuclease T I is 2.9 , so net charge at pH 1.5 is POSITIVE.

pI of Cysteine is 5.07 , so during paper electrophoresis at pH 4.3, it has a net positive charge , so it will move towards the negative electrode.

pI of Phenylalanine is 5.48. so at pH 4.5, is has a net positive charge and it will move toward negative electrode

pI of papain is 9.6. Net charge on papain at pH5.1 is POSITIVE.

pI of lipase B is 5. net charge at pH 7.3 is NEGATIVE.

pI of asparagine is 5.41 at pH 6.5,it has a net negative charge, it moves towards the POSITIVE electrode.

pI of glycine is 5.97 , at PH 7.1 , it has a net negative charge , so moves towards the POSITIVE electrode.

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