[uzi4u2]

WoW borek straight up answer 
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

[xiankai]

try to show your work too...

[uzi4u2]

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 

[Yggdrasil]

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

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.

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.

[uzi4u2]

but i have a problem with the Michaelis-Menten  equation since there are like 3-4 versions of it , which one do i use ?
 

[Yggdrasil]

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 (V_max), you should probably choose one in the form:

V = blah

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

[uzi4u2]

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 :/

[sdekivit]

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.

[Yggdrasil]

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.

[sdekivit]

Quote from 'Biochemistry' by Berg et al:

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

[Yggdrasil]

I would say that when > 100Km, you can say that >> Km and V ~ V_max, 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 

[uzi4u2]

okay but then ...like 9 AND 10 are possible answers, so which one to pick ?