What is the structure of the peptide P-A-I-G-E at a pH of 7 and 12? What is the isoelectric point?
Proteins
We generally tend to think of proteins only from a dietary lens, as a component of what we eat. However, they are among the most important and abundant organic macromolecules in the human body, with diverse structures and functions. Every cell contains thousands and thousands of proteins, each with specific functions. Some help in the formation of cellular membrane or walls, some help the cell to move, others act as messages or signals and flow seamlessly from one cell to another, carrying information.
Protein Expression
The method by which living organisms synthesize proteins and further modify and regulate them is called protein expression. Protein expression plays a significant role in several types of research and is highly utilized in molecular biology, biochemistry, and protein research laboratories.
What is the structure of the peptide P-A-I-G-E at a pH of 7 and 12? What is the isoelectric point?
Peptides are composed of amino acids that are bonded to each other via peptide bonds. The ionizable groups in a peptide are the N-terminal amino group, C-terminal carboxyl group and ionizable side chains of some amino acids.
All ionizable groups have their characteristic pKa value.
pKa is the pH at which half of all the molecules will have the group in protonated state while the rest half of the molecules will have the group in deprotonated state.
When the pH is below the pKa of a group, the group will predominantly exist in its protonated state. When the pH is above the pKa of a group, the group will predominantly exist in its deprotonated state.
Ionizable groups can be broadly classified as acidic and basic groups.
Acidic groups are neutral in protonated state while at deprotonated state they possess a negative charge. The C-terminal carboxyl group, side chain of aspartate (Asp) and side chain of glutamate (Glu) are acidic groups.
Basic groups have a positive charge in protonated state while they are neutral in deprotonated state. The N-terminal amino group, side chain of arginine (Arg), side chain of lysine (Lys) and side chain of histidine (His) are basic groups.
Even though the side chain of cysteine and tyrosine are not termed strictly acidic (as their pKa values are above 7), they too behave like acidic groups i.e. neutral in protonated state while at deprotonated state they possess a negative charge.
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