6. Would Lys-Glu-Ser have the same pl as Ser-Glu-Lys? Explain.7. For a protein, how do you think you might estimate the pI?8. Draw a dipeptide (use R, and R, for the side chain R groups) and the resonance structures of the peptidebond.9. Recall the geometry about atoms that participate in double bonds or partial double bonds. What atomsform the rigid plane of the peptide bond (which atoms are coplanar)?10. How do you expect the rigid plane of the peptide bond to impact folding? The pl of a peptide is determined by examining the ionizable groups. The protonated and unprotonatedforms of each ionizable group are in equilibrium. Consider the peptide Lys-Glu-Ser shown below at pH7.2. The complete structure is on on the left and a stylized structure with just the ionizable groups is on theright. While the N-terminal is depicted as protonated, a sample of Lys-Glu-Ser is composed ofa populationof molecules and within that population some molecules may contain a non-protonated N-terminal groupat pH 7.2.Model 2:COO-H,N*.pK,= 3.5N-CH-C N CH- -0-H.OH:-pK= 8.5H,N*-CH-C-H.COO-NH;*pK= 10.0CH2pK=4.2CH2CH2一CH2OHCH2CH2C0CH2NH,*In the stylized structures below, only one molecule is drawn. However each diagram represents a collectionof many molecules. Therefore "half protonated" implies that half the molecules present are protonated andhalf are not.HạN-COOHH3N*--COOH/COO-H3N-COO-OHOHCOOHNH3COOHNH3СООНNH3 COO-At pH=1 all groups are protonated.At pH=3.5 the C terminal is half proton-ated and half deprotonated.At pH=4.2 the R group carboxyl is halfprotonated, half deprotonated.NET charge = 0.5NET charge = +2NET charge = +1.5H3N*/H,NCOO-H2NCOO-H2N-OHCOO-CO0-NH,OHCOO-OHNH3 /NH2COO-At pH=8.5 the N terminal is halfprotonated and half deprotonated.NH2At pH=10.0 the R group amino of lysineis half protonated, half deprotonated.NET charge -0.5At pH=12 all groups are deprotonated.%3DNET charge = -1.5NOTE: In peptides and proteins, the N-terminal and C-terminal groups have different pK,s from the parentamino acid. The pK, of the N-terminal is about 8.5 whereas C-terminal pK, is about 3.5NET charge =-2.0

Name: 6. Would Lys-Glu-Ser have the same pl as Ser-Glu-Lys? Explain.7. For
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Description: 6. Would Lys-Glu-Ser have the same pl as Ser-Glu-Lys? Explain.7. For a protein, how do you think you might estimate the pI?8. Draw a dipeptide (use R, and R, for the side chain R groups) and the resonance structures of the peptidebond.9. Recall the