biochem question on protein

Prep for USMLE Forum

» Log in | Register

Forum

Step 1

Match

Prep4USMLE Forum » USMLE Step 1 Forum » Biochemistry Forum

biochem question on protein

Author

8 Posts

littlelady
Forum Newbie

Topics: 3
Posts: 7

10/05/07 - 09:11 PM

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

drgho
Forum Junior

Topics: 1
Posts: 115

10/05/07 - 10:48 PM

B. Agree

littlelady
Forum Newbie

Topics: 3
Posts: 7

10/05/07 - 11:27 PM

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

drgho
Forum Junior

Topics: 1
Posts: 115

10/06/07 - 01:57 AM

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?

littlelady
Forum Newbie

Topics: 3
Posts: 7

10/06/07 - 10:11 AM

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

littlelady
Forum Newbie

Topics: 3
Posts: 7

10/07/07 - 08:53 PM

I GOT THE ANSWER..... smiling face

THANKS

bioguy
Forum Guru
avatar

Topics: 46
Posts: 803

10/09/07 - 04:44 PM

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

new_n_lost
Politically InCorrect
avatar

Topics: 650
Posts: 6,061

10/09/07 - 05:23 PM

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."

You don't have permission to post.