Hello, dear friend, you can consult us at any time if you have any questions, add  WeChat:  zz-x2580

Laboratory 1 hand in sheet

Part 1:

1. What shape is the curve in the first graph?

[1 mark]

2. Why is it sensible to blank the spectrophotometer using tube #11 instead of tube #1?

[2 marks]

3. Insert the graphs you have drawn into your report, with appropriate brief figure legends. 

[6 marks]

4. Use your graphs to determine the pKa of the ionization of the tyrosine sidechain. Show your workings.

[2 marks]

5. Using the Henderson-Hasselbalch equation, calculate the % ionization of a tyrosine side-chain in the cell. Use the value you determined in Question 4, and assume that the cytosol is buffered at pH 7.35. Show your working.

[2 marks]

6. What consequence does this ionisation state have for the role of tyrosine residues in proteins?

[2 marks]

Part 2:

7. How many α-helices are there in the protein?

[1 mark]

8. How many β-strands make up the β-sheet?

[1 mark]

9. Is the topology of the β-sheet parallel, anti-parallel or mixed?

[1 mark]

Use the Henderson-Hasselbalch equation to answer Questions 10 and 11. Show your workings for both questions.

10. The pKa of the –SH group of free cysteine is 8.35. The cytosol of human cells is normally pH 7.35 What would be the % ionization of the –SH group of free cysteine in the cytosol?

[2 marks]

11. The pKa of the active site cysteine in a 1-Cys Prx enzyme has been measured at 6.2. What would be the % ionization of the –SH group of the Prx active site cysteine in the cytosol?

[2 marks]

12.  Give the name and residue number for each of the amino acid residues that have side chains within 4? of the sulfur atom in Cys47.

[1 mark]

13. What feature of the local environment around Cys47 might stabilize the existence of a thiolate ion?