SOS Part 1 - Concept review 1. Amino Acid Composition & pl. Use the Compute pl/M

Question

SOS
Part 1 - Concept review 1. Amino Acid Composition & pl. Use the Compute pl/MW" tool at the ExPAS Bioinformatics Resource Portal Ihttp:l/web.expasyorg/compute pi/) to compute the theoretical pl for each of the following peptides. Rank these from lowes pl (5) AAAEEe 3.0 3.8 How is amino acid composition trends. affecting the pl of these peptides? Describe any observed 2. Protein pl vs. pH. Approximate the overall net charge (as either t,, or 0) on the following proteins at the indicated pH values. Approximate Overall Charge at pH: 4.0 Proteinpl 5.0 7.0 8.0 9.0 10.0 6.0 5.4 ( 6.8() C 7.5 8.6 )) 9.3

Explanation / Answer

1.As the pI values have already been calculated and arranged in increasing order.

The amino acids present in the above five peptide chains is-

A - Alanine , which is a Non polar amino acid without any charge.

E - Glutamic acid, which is a acidic amino acid with negative charge

R- Arginine , which is a basic amino acid with positive charge.

So seeing the trend in the peptide-

AAEEE - more acidic amino acids

AAAEE- more neutral amino acids

AAAAA- all neutal amino acids

AAARR- Basic amino acids

AARRR- More basic amino acids.

So it is known that proteins that have presence of basic amino acids will have higher pI and those having acidic amino acids will have lower pI and this trend is following here too.

From left to right, acidic amino acids are changing to badic amino acids and therefore the pI is increasing.

2. At pH values above pI , the protein has a negative charge.

and at pH values below pI , the protein has positive charge.

So you have correctly put the +,- charge on each of them.

Hope it helps , Good luck !!!

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