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Topic: Re: 3 questions i just cant solve , can you ?  (Read 13225 times)

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Offline uzi4u2

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Re: 3 questions i just cant solve , can you ?
« on: August 20, 2006, 09:04:49 AM »
WoW borek straight up answer  :D
I will take it !
well since i am already here and i dotn want to open up another post here are some questions which i didnt manage to solve today :

1. Hemoglobin and myoglobin both :
      1)bind nem in a hydrophobic pocket
      2)are highly alphahelical
      3)bind one molecule of nem per globin chain
      4)bind one 2,3bisphosphoglycerate per molecule
 
      possible answers :    a]2,3   b]1,2,3,4      c]3     d]1,4   e]1,2,3

2.what is rate of enzyme reaction when the substrate concentraitor is ten times higher than its Km and maximum rate is 10v  ?
      1)9
      2)8
      3)10
      4)0.9
      5)0.1

3.active site of all serine proteases contain
      1)Asp
      2)Glu
      3)His
      4)Ser


again thanks for yer help :)
« Last Edit: August 20, 2006, 09:28:46 AM by uzi4u2 »

Offline xiankai

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Re: 3 questions i just cant solve , can you ?
« Reply #1 on: August 20, 2006, 10:48:06 AM »
try to show your work too... ;)
one learns best by teaching

Offline uzi4u2

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Re: 3 questions i just cant solve , can you ?
« Reply #2 on: August 20, 2006, 11:04:17 AM »
well if i would have known anything about it i would have showen but i have no idea  ???
thats why i have nothing to show  ;D

Offline Yggdrasil

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Re: 3 questions i just cant solve , can you ?
« Reply #3 on: August 20, 2006, 11:32:14 AM »
1. Hemoglobin and myoglobin both :
      1)bind nem in a hydrophobic pocket
      2)are highly alphahelical
      3)bind one molecule of nem per globin chain
      4)bind one 2,3bisphosphoglycerate per molecule
 
      possible answers :    a]2,3   b]1,2,3,4      c]3     d]1,4   e]1,2,3

1. If nem stands for oxygen, then false.  The oxygen binding pocket contains a charged iron atom which binds to the lone pairs of the oxygen.
2. True, just look up the structures of the two molecules in a biochemistry text.
3. If nem stands for oxygen, then true.  Although hemoglobin binds 4 oxygen molecules, it consists of four globin chains which each bind one oxygen.
4.  False, myoglobin cannot bind BPG.  BPG binds to the "hole" formed in the middle of the tetramer of hemoglobin chains.  More on BPG here:  http://en.wikipedia.org/wiki/2%2C3-bisphosphoglycerate

Quote
2.what is rate of enzyme reaction when the substrate concentraitor is ten times higher than its Km and maximum rate is 10v  ?
      1)9
      2)8
      3)10
      4)0.9
      5)0.1

Look up the Michaelis-Menten equation and just plug in your values.

Quote
3.active site of all serine proteases contain
      1)Asp
      2)Glu
      3)His
      4)Ser

This is a weird question, because the serine proteases contain a catalytic triad consisting of an aspatate, a histadine, and a serine.  The negatively charged aspartate interacts with the histadine, increasing the pKa of the histadine (i.e. the his becomes more basic).  This allows the histadine to deprotonate the serine, which creates an oxyanion capable of performing nucleophilic attack on the amide bond of a protien.  So, options 1, 3, and 4 are correct.

More on serine proteases here:  http://en.wikipedia.org/wiki/Serine_protease
See catalytic mechanism especially.

BTW, these sets of questions should be in the biochemistry section.

Offline uzi4u2

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Re: 3 questions i just cant solve , can you ?
« Reply #4 on: August 20, 2006, 12:18:56 PM »
but i have a problem with the Michaelis-Menten  equation since there are like 3-4 versions of it , which one do i use ?
 :o

Offline Yggdrasil

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Re: 3 questions i just cant solve , can you ?
« Reply #5 on: August 20, 2006, 12:37:48 PM »
They should all give the same answer, so just try using the one that looks most useful to you.  Since you're looking for the rate (V) and you're given the concentration of substrate () and the maximum velocity (Vmax), you should probably choose one in the form:

V = blah

where blah has and Vmax in it.  (if it's helpful, k2[E0] = Vmax).

Offline uzi4u2

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Re: 3 questions i just cant solve , can you ?
« Reply #6 on: August 20, 2006, 01:46:38 PM »
okay i used this equation :


Vmax* /  Km+ 

so :  Vmax=10
       = x
       Km= 10x

             10*x  / 11x  = 0.909    now there is such an answer but i am not sure its correct :/

Offline sdekivit

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Re: 3 questions i just cant solve , can you ?
« Reply #7 on: August 20, 2006, 05:20:22 PM »
when >> Km ( in general starting when = 5 * Km) then V = Vmax

--> thus the answer is 10 (Vmax).

you can easily see this in the formula:

V = Vmax * / ( + Km)

When >> Km then the equation will look like V = Vmax * / and thus V = Vmax, as in this case.

Offline Yggdrasil

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Re: 3 questions i just cant solve , can you ?
« Reply #8 on: August 21, 2006, 12:26:21 AM »
the substrate concentraitor is ten times higher than its Km

This means = 10x, Km = x, not what you wrote.

Therefore, v = (10 * 10x) / (x + 10x) = 100/11 = 9.09, so I'd say that option (1) is the correct answer.

Offline sdekivit

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Re: 3 questions i just cant solve , can you ?
« Reply #9 on: August 21, 2006, 04:18:31 AM »
Quote from 'Biochemistry' by Berg et al:

'At high substrate concentration, when is much greater than Km, V0 = Vmax: that is, the rate is maximal, independant of substrate concentration'


Offline Yggdrasil

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Re: 3 questions i just cant solve , can you ?
« Reply #10 on: August 21, 2006, 12:12:05 PM »
I would say that when > 100Km, you can say that >> Km and V ~ Vmax, and in doing so the error will be less than about 1%.  When = 10Km, the difference is only one order of magnitude, so you get errors of about 10% (which is the difference between 10 and 9).

Plus, biologists are horrible mathematicians  ;)

Offline uzi4u2

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Re: 3 questions i just cant solve , can you ?
« Reply #11 on: August 21, 2006, 03:42:40 PM »
okay but then ...like 9 AND 10 are possible answers, so which one to pick ?

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