3021 Problem Set 1.doc

Print Name: __________________________ Author Number: _____ BioC 3021 Section 001 Problem Set 1 Due: at the start of class on Tuesday, February 2 Answer these questions by yourself, do not work with anyone else. You may use books or notes. 1. All these amino acids have R groups that can form hydrogen bonds that are important to protein tertiary structure EXCEPT: (1 point) a. asparagine b. aspartic acid c. phenylalanine d. serine e. tyrosine 2. Estimate the percent of cysteine molecules that will have the sulfhydryl group hydrogen dissociated at pH 9.5. The pKa for the cysteine side-chain sulfhydryl group is 8.3. (1 point) a. 44% b. 21% c. 3% d. 52% e. 91% 3. What is the overall net charge on the peptide C-H-V-L-E at pH 5.2? (1 point) a. +2 b. +1 c. 0 d. -1 e. -2 4. Calculate the pH at which the R-group amino group of lysine is 33.3% dissociated. The pKa for this group is 10.5. Show your work. You might need some of the following logs: (2 points) log 10 = 1.00 log 8 = 0.90 log 6 = 0.78 log 4 = 0.60 log 2 = 0.30 log 1 = 0 log 0.5 = -0.30 log 0.25 = -0.60 log 0.167 = -0.78 log 0.125 = -0.90 log 0.1 = -1.00 5. Draw a complete titration curve for the amino acid arginine similar to the one on page 11 of the course packet. The X-axis should be ?moles OH- added / mole HA? and the Y-axis should by ?pH?. Draw the titration curve and indicate any pK values that might be present. Above the curve, draw the structure of the amino acid in its starting form, its ending form, and any additional forms it might have during the titration. (3 points) 6. Draw all atoms of the peptide G-Q-P-H-E-R. Draw a circle around each peptide bond. Assume pH = 9.1. (2 points) PAGE 2 __________ | |