Test question: pI and pH

[monkily_stealth]

Hey guys, I'm using this answer key to an old Biochem test for studying, but I don't understand the answer to Question 4a. Shouldn't the answer be Proteins A, D, and E? (link to answer key). (If you don't want to click that link, I copied the problem below, along with my ideas). Thank you in advance!

Edited December 4, 2009 by monkily_stealth

[CharonY]

Moved to the homework area. Also it would help if you would just shortly copy the question in here instead of using a link. Spammers are everywhere.

[monkily_stealth]

Sorry about that! I couldn't seem to get it in a decent looking format by copy-pasting, but here goes:

 

 

QUESTION: Mustard gas, Cl-CH2-CH2-S-CH2-CH2-Cl (also known as HS or Yperite) is an inexpensive, easily manufactured and highly effective blistering agent. Although fatalities are rare, victims frequently suffer blindness, agonizing burns, long term respiratory damage, permanent incapacitation, and drastically reduced lifespans. The agent is also persistent - casualties can result from individuals taking shelter in contaminated soil. You have discovered an enzyme from a rare species of Bolivian poison dart frog that inactivates mustard gas, converting it into an effective deodorant. The battlefield uses are obvious.

 

 

 

Your initial extract contains several proteins with the following properties:

 

 

 

Protein

Molecular Weight

pI

Shape

 

A

83,000

5.1

Globular

 

B

12,000

7.5

Globular

 

C

41,000

7.9

Globular

 

D

33,000

5.4

Globular

 

E

33,000

5.1

Rod-shaped

 

F

83,000

8.2

Globular

 

a. I apply the mixture to a chromatographic column containing an an anion exchanger (Diethylaminoethylcellulose) buffered at pH 6.5. Based on your knowledge of pH and pI, and of ion-exchange chromatography, which proteins will stick to the column at this pH? (5 pts)

 

 

 

ANSWER KEY: B and C have a negative charge at pH 6.5 and will stick to the column

 

ME: See, I would have said A,D,E because those proteins' pI's are below the buffer pH of 6.5, which would make them negatively charged, and therefore bound to the column. Right?

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Merged post follows:

Consecutive posts merged

Anyone... Bueller...? This doesn't seem very difficult, I just think the teacher was wrong, which is throwing me off...

[CharonY]

If the pI is lower than the ph of the buffer they will be negatively charged, yes.