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Kaplan Qbank USMLE



Author8 Posts
  #1

2) Denatured proteins
(‘1’) have higher viscosities than their native conformation counterparts.
(‘2’) have higher water water-accessible surface area compared to their native
conformation counterparts.
(‘3’) have lost their biological activity.
(‘4’) may have more titrable residues per molecule than their native conformation
counterparts.

A) if 1, 2, 3 are correct
B) if 1 and 3 are correct
C) if 2 and 4 are correct
D) if 4 only is correct
E) if all are correct

I think the answer is B but not sure..my friend had E. not sre who is right here



  #2

B. Agreenod

  #3

I have a another question that my friend and I are not agree. I dont know if you can help

15) If you had 100.0mL of 1.0M of the peptide in question #12, what must you add to adjust the
pH from point “D” on the titration curve in question #12 to achieve a pH of 4.0? Assume
you have available 1.0M NaOH and 1.0M HCl.
A) 200.0mL HCl
B) 67.0mL HCl
C) 67.0mL NaOH
D) 167.0mL HCl
E) 33.0mL HCl

This is the GRAPH

http://img264.imageshack.us/img264/7143/22702495q...



This is what I did. I picked A to be my answer...

PH =PKA + log ( basé / acid )

4 = 4.74 + log ( 1.0 x 100) / ( 1.0 x 200 )


Did I do it right?? my friend got 167 ml HCL...i dónt know who is right




  #4

I think is 167 ml of 1.0M HCl. The soultion has 0.1 mole of protein. So at point D where NaOH/Protein ratio is 3 and NaOH should be 0.3 mole at point D. And the target is pH 4 with the NaOH/Protein ratio is approximately 1.33 which means targeted NaOH mole is 0.133. So, it is needed to neutralise 0.167 mol of NaOH which can be done by adding 167ml of 1.0M HCl. Btw, are those MLE questions? I feel it is nothing to do with treating the patients. What kind of scenario did the question give?

  #5

Thank DRHHO nod u'RE RIGHT !! smiling face i have the last question for u sticking out tongue if you know it


12) Use the following information for this question:
You have isolated an unknown peptide whose titration curve is shown below. The peptide
absorbs ultraviolet radiation at 280nm. Treatment with trypsin released free alanine and
arginine. Treatment with chymotrypsin resulted in quantitative production of a neutral
tripeptide and an alkaline dipeptide.


( Tripsin cut the peptide at basic charge such as lysine and arginine, chymotrypsin cut anyone acids that has Aromatic rings such as Tryptophan )......

This is the graph

http://img264.imageshack.us/img264/7143/22702495q

this is the table of Pk amino acid

http://www.dbs.umt.edu/courses/fall2006/bioc380/l...

the question is


The most likely structure of the peptide is
A) Arg-Glu-Trp-Lys-Ala
B) Ala-Lys-Trp-Glu-Arg
C) Arg-Trp-Lys-Glu-Ala
D) Arg-Glu-Lys-Trp-Arg-Ala
E) Lys-Arg-Ala-Trp-Glu-Ala

I think it's B but my friend had A. A and B are the same..i dont know what's the different

  #6

I GOT THE ANSWER..... smiling face THANKS

  #7

I HATE this part of biochemistry. Do you really get such questions in the Step 1 test?????????????

  #8

bioguy wrote:
I HATE this part of biochemistry. Do you really get such questions in the Step 1 test?????????????

OH HE** NO

I wud rather change my field if i had to bear such lame and pointless calculations.


___________________
FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."







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