Concept explainers
Interpretation
The Isoelectric point (pI) of proline is to be calculated. In an electrophoresis experiment, will proline migrate at
Concept introduction:
Electrophoresis is a common way of separating a mixture of amino acid. In electrophoresis, any ion that has a net positive charge, at that pH, will migrate toward the negatively charged terminal whereas any ion having a net negative charge will migrate toward the positively charged terminal.
An amino acid’s pI is the average of its two pKa values associated with the zwitterion- the pKa value corresponding to the proton transfer reaction in which the zwitterion is a product, and the pKa value corresponding to the proton transfer reaction in which the zwitterion is a reactant.
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ORGANIC CHEMISTRY E-BOOK W/SMARTWORK5
- Answer the following questions about the amino acid whose Fischer projection formula is a. Is it a D-amino acid or an L-amino acid? b. Is it a nonpolar or polar amino acid? c. Is it an essential or nonessential amino acid? d. Is it a standard or nonstandard amino acid?arrow_forwardSingle hydrolysis on the following polypeptide 2. Draw the fisher projection of phenylalanine at pH 1, 7 and 12arrow_forward(a) The isoelectric point (pI) of phenylalanine is pH 5.5. Draw the structure of the major form of phenylalanine at pHvalues of 1, 5.5, and 11.(b) The isoelectric point of histidine is pH 7.6. Draw the structures of the major forms of histidine at pH values of 1, 4,7.6, and 11. Explain why the nitrogen in the histidine ring is a weaker base than the a-amino group.(c) The isoelectric point of glutamic acid is pH 3.2. Draw the structures of the major forms of glutamic acid at pH valuesof 1, 3.2, 7, and 11. Explain why the side-chain carboxylic acid is a weaker acid than the acid group next to thea-carbon atomarrow_forward
- Draw the structure of alanine in a solution at pH = 0arrow_forwardFor each amino acid [RCH(NH2)COOH], draw its neutral, positively changed, and negatively charged forms. Which form predominates at pH = 1, 6, and 11? What is the structure of each amino acid at its isoelectric point?a. methionine (R = CH2CH2SCH3)b. serine (R = CH2OH)arrow_forward1. At what pH is the side chain of arginine 65% ionized? 2. At what pH is glutamate 25% ionized? 3. At what pH is the side chain of histidine 4/5 ionized? 4. At what pH is the side chain of cysteine 15% ionized? 5. At what pH is tyrosine 5/8 ionized?arrow_forward
- 1. (a) Draw a circle around one amino acidin the structure. ( b) Draw a box around one amino acid side chain. (c) Indicate whether the side chain you chose is hydrophobic or hydrophilic. (d) Draw an arrow pointing to a peptide bond 2. If the peptide segment shown above was part of a beta sheet, which of its functional groups would be involved in forming and stabilizing the beta sheet? 3. Which amino acid (also called amino acid residue)would be more likely to occur on the surface of a protein: an aspartate residue or a methionine residue? Explain your choice.arrow_forwardWhat is the isoelectric point for the peptide MNPQR at pH 7? Draw the structure, including the stereochemistry of each C-alpha chiral center.arrow_forwardWhat percentage of the a-amino group of lysine will be protonated at its pI? < 25% 50% > 75% a. Answer the same question for the e-amino group of lysine.arrow_forward
- Although tryptophan contains a heterocyclic amine, it is considered a neutral aminoacid. Explain why the indole nitrogen of tryptophan is more weakly basic than one ofthe imidazole nitrogens of histidine.arrow_forwardUsing resonance structures, show why the amino group is activating. Consider an attack by the electrophile E+ at the para position.arrow_forwardWhat is the correct structure for the peptide SGHKRY at pH 5.0?arrow_forward
- Organic And Biological ChemistryChemistryISBN:9781305081079Author:STOKER, H. Stephen (howard Stephen)Publisher:Cengage Learning,General, Organic, and Biological ChemistryChemistryISBN:9781285853918Author:H. Stephen StokerPublisher:Cengage LearningIntroduction to General, Organic and BiochemistryChemistryISBN:9781285869759Author:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar TorresPublisher:Cengage Learning