mtK - Net ID 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14....

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Net ID KEY BIO3310 MIDTERM EXAM 10/22/09 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. TOTAL BE SURE TO WRITE/PRINT  LEGIBLY . IF WE CAN'T READ IT, WE CAN'T GRADE IT! (SERIOUSLY) PRINT NAME (LAST, FIRST) ON THE BACK TOP OF THE LAST PAGE AND ONLY THE LAST PAGE Use these pK a values unless others are given in a problem: terminal COOH 4 terminal NH 3 + 9 R-GROUPS: Asp 4 Glu 4 Cys 8 Tyr 10 His 7 Lys 10 Arg 12
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
1. (7 pts) 20 different amino acids are incorporated into proteins on the ribosome. a. At physiological pH every one of the 20 free AA has at least two ionizable groups. -COO- and NH3+ On the right, draw just these two charged groups. b. In proteins, only 7 of these AA need to be considered for formation of ion pairs. Below, BRIEFLY explain why just 7 (not 20): ONLY THESE 7 ARE IONIZABLE, THE OTHERS NOT! c. Ala, Val, and Leu are each highly water-soluble as the free AA. But the small peptide (Ala-Val-Leu) 3 is not very water-soluble. Below, BRIEFLY explain these observations: FORMATION OF THE TWO PEPTIDE BONDS RESULTS IN LOSS OF 2 POS CHARGES AND 2 NEG CHARGES 2. (5 pts) Many ion pairs are found in the Hb T-state but not in the R-state. a. One type is Arg-Asp. Approximately what fraction of the Arg-Asp are actually in ion pairs at pH = 7.2? 1.0 b. Another type is His-Asp. Exactly what fraction of the His-Asp are actually in ion pairs at pH = 7.2? 0.4 pH = pKa + log[un]/[prot] for Asp at pH 7.2, this fraction is 0.999 for His: 7.2 = 7.0 + log[un]/[prot], so 0.2 = log[un]/[prot], thus [His]/[His+] = 1.6, hence fraction His+ = 1/2.6 = 0.4 3. (6 pts) A piece of information: A protein in water can last for years, yet hydrolysis of each peptide bond is thermodynamically favorable. a. In a graph on the right, illustrate this information. Assume no additional information. Label axes. b. A protease is added. Now the reaction is complete in seconds. Add dotted lines to your graph to show this additional information. 4. (6 pts) Draw the tripeptide Ala-Gly-Ala. The Ala side chain is CH 3 , the Gly side chain is H. Choose only one peptide bond, and circle only the 6 atoms that lie in a plane . Choose any one of the C α and draw and label arrows to the bond allowing Φ and the bond allowing Ψ rotation. Show the correct form of any ionizable groups at pH = 7.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/19/2010 for the course BIOBM 3310 taught by Professor Feigenson,gw during the Fall '07 term at Cornell University (Engineering School).

Page1 / 8

mtK - Net ID 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14....

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online