8/9/2023 0 Comments Calculate pi of peptide chain![]() ![]() Since the termini had a net charge of 0, the overall net charge of the given peptide is also -2. Both have acidic side chains that will be deprotonated in a solution of pH 8, and therefore contribute a -1 charge each, for a net charge of -2. VIDEO ANSWER: The side chain acidic nature of cysteine is given as pKa1 value plus pKa2 value divided by 2, where the pKa1 value is for the carboxylic acid. We only need to take note of the basic and acidic amino acids which, in this case, are aspartic acid (D) and glutamic acid (E). Because the side chains of these amino acids will never be charged, we can ignore them when looking for the net charge of the peptide. In our example, these amino acids are: Alanine (A), asparagine (N), leucine (L), isoleucine (I), phenylalanine (F), and proline (P). Logically, any polar and nonpolar amino acids will not be carrying labile protons and, therefore, will not be charged within our solution. So now that we’ve dealt with the N and C termini, we need to consider the charges on our residues. This also suggests that we are likely to only care about the contribution from our N and C termini in extreme environments, in cyclized peptides or in post-translationally modified ones. Consequently, we can expect a -1 charge on the carboxylate group and a +1 on the amine, for a total of zero for the two termini. So, if we are in an environment of pH of 8, we can expect the carboxyl group to be deprotonated and the amino group to still be almost exclusively protonated. Recall from that post that the carboxylic acid terminus on an amino acid has a pKa of approximately 2, while the terminal amine has a pKa of approximately 9. In another post, we discussed how to determine the charge state of certain amino acid functional groups, given the pKa of those groups and the pH of the surrounding solution. Residency Advising Complete Match Support.Application Advising Medical School Admissions Support.Direct Medical (BS/MD & BA/MD) Application Consulting.MCAT Prep App Videos, Flashcards & Q-Bank.MCAT Tutoring One-on-One Personalized Help.MCAT Masterclass Videos, Questions, Notes.Med School Explorer Find Your Medical School Path.Virtual Shadowing Explore Medical Specialties.ERAS Personal Statement Refine Your Story.Application Advising Residency Match Support.Ontario Application Support OMSAS Application.CASPer Preparation Simulation & Coaching.Interview preparation Realistic Practice.Secondary Editing Secondary Application Editing.Personal Statement Editing Refine Your Narrative.STRATEGIC PLANNING Early Planning for Success.Application Advising Complete Admissions Support.Interview Preparation Realistic Practice. ![]() Strategic Planning Early Planning for Success.College Admissions Consulting Built for Pre-Meds.MCAT CARS Mastery Top-Rated CARS Video Course.MCAT Prep App Videos, Flashcards, Q-Banks.MCAT Tutoring Complete One-on-One Personalized Help.Frequently Asked Questions Find answers.For Parents Learn why you should trust us.Success Stories & Testimonials Hear the stories. ![]()
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