Peptides

 How many atoms compromise a repeating unit of a peptide backbone? 6 atoms:amide nitrogen & its Halpha carbon & its Hcarbonyl carbon & its O (See slide #22) What is the minimum # of ionizable functional groups that can present itself in a peptide or a free amino acid? What are these functional groups? 2: amino (NH3+) & carboxylate (COO-) how to calculate the # of peptide bonds from the # of amino acids # of peptide bonds = # of amino acids - 1 (Ex. 575 amino acids = 574 peptide bonds) Determine the total # of ionizable amino acids & total # of ionizable groups in the peptide sequence H3N+ - ELGSAHVK - COO- 4 ionizable amino acids: ESHK6 ionizable groups: ESHK, NH3+, and COO- (Ionizable amino acids: CDESTY HKR) Determine the # of stereoisomers of the peptide sequence H3N+ - QLTVGYARWIE - COO- (11 total amino acids) - (1 for G) + (2 more chiral centers for I & T) = 12 total chiral centers 2^12 = 4096 stereoisomers A peptide has a total of 4,196,352 possible stereoisomers. How many chiral centers does it have? (2)^n = # of stereoisomers [log (2)^n]/log 2 = [log (4,196,352)]/log 2 = 22 chiral centers Determine the length (in amino acids) of a peptide that has 8192 stereoisomers. There are 2 Gs, 1 I, & 1 T residues. Length of peptide = (total # of chiral centers + total # of G residues) - (total # I & T residues) [log (8192)]/log 2 = 13 chiral centers Length of peptide = (13+2) - (1+1) = 15 - 2 = 13 Trypsin cleaves peptide bonds __ C-terminal (to the right of) Lys (K) & Arg (R) except when they are the last residue. (cannot be right next to COO- at the end) Other exception: Pro (P) cannot be to the right of Lys & Arg. (Pro cannot be cleaved.) See slide #30 Chymotrypsin cleaves peptide bonds __ C-terminal (to the right of) Phe (F), Tyr (Y), Trp (W) except when they are the last residue. (cannot be right next to COO- at the end) Other exception: Pro (P) cannot be to the right of Phe, Tyr, Trp. (Pro cannot be cleaved.) See slide #31 Cyanogen bromide turns __ into a homoserine (Hsr). Met (M). After Met, the peptide would be cleaved off. Ex. If using cyanogen bromide results in a tetrapeptide composed of Hsr & 3 other residues, Met wouldâ€™ve been the last residue in that tetrapeptide. (See slide #29 & problem set 1 #38) If one cycle of Edman degradation produces PTH-Tyr, where does Tyr go in the peptide sequence? In the very beginning of the sequence next to H3N+ (N-terminus). An Edman degradation technique identifies the amino terminal residue of a peptide. (See slide #28 & problem set 1 #38) Authorsophathida ID350542 Card SetPeptides DescriptionPeptides Updated2020-02-02T19:24:15Z Show Answers