[uzi4u2]

good morning people !  i have a chemistry final and i cant sleep because of this darn question ! please help

In the alfa helix the hydrogen bonds : 
 A) occur only between some o the amino acids of the helix
 B)occur mainly between electronegative atoms of the backbone
 c) occur mainly between electronegative atoms of the R groups
 d)are perpendicular to the axis of the helix
 e)occur only near the amino and carboxyl termini of the helix

I narrowed it down to either A Or B
also a small other question :

In competitive inhibition an inhibitor lowers the Vmax of the enzyme OR binds reversibly at the active site?

[Yggdrasil]

I would say B is the correct answer.  Alpha helices are stabilized primarily by backbone hydrogen bonds.

A competitive inhibitor is defined as an inhibitor which binds reversibly at the active site.  Competitive inhibitors do not lower the V_max of the enzyme since high concentrations of substrate can outcompete the inhibitor from the active site.  Competitive inhibitors, however, will raise the apparent k_m of the enzyme since a larger concentration of substrate will be needed to reach V_max.

[uzi4u2]

thank you !

[refid]

A competitive inhibitor is defined as an inhibitor which binds reversibly at the active site.  Competitive inhibitors do not lower the V_max of the enzyme since high concentrations of substrate can outcompete the inhibitor from the active site.  Competitive inhibitors, however, will raise the apparent k_m of the enzyme since a larger concentration of substrate will be needed to reach V_max.

For competitive inhibitor,  will the V_max increase since the k_m=1/2V_max ?

Just curious, for non-competitive inhibitor, would the V_max,k_m all go to zero, same for irreversible inhibitors?

[Yggdrasil]

The actual k_m of the enzyme does not change in the presence of a competitive inhibitor.  However, the apparent k_m, defined by the concentration of substrate at which V = (1/2)V_max, does increase.  See the following figure:

http://www.steve.gb.com/images/science/competitive_inhibition_kinetics.png
The green trace represents uninhibited enzyme and the red trace represents enzyme in the presence of competitive inhibitor (the graph isn't entirely accurate, but it gives a good enough picture).

Irreversible inhibitors (e.g. suicide inhibitors which irreversibly bind the enzyme) will lower the effective [E].  If all of the enzyme is bound by a suicide inhibitor, then your V_max will go to zero.  A suicide inhibitor will not change the apparent k_m of the reaction.

For other types of inhibitors, you can see different effects depending on the mechanism of action of the inhibitor (e.g. does the inhibitor bind the enzyme alone, does it bind the enzyme-substrate complex, does it have equal affinity for apo-enzyme and enzyme-substrate complex?)

(note: I'm moving this to the biochem forum since it's more about biochem than organic chem)

[refid]

(note: I'm moving this to the biochem forum since it's more about biochem than organic chem)

Yess this thread turn bio quick ... the image give this following msg :Forbidden You don't have permission to access /images/science/competitive_inhibition_kinetics.png on this server.

is it alright if you post it so I can see?

[Yggdrasil]

Here are some similar images you could look at (found in google search):

http://wiz2.pharm.wayne.edu/biochem/COMPET.GIF
http://www.examstutor.com/biology/resources/studyroom/biochemistry_and_cells/enzymes/pictures/with_without_graph.gif

[refid]

ahh i see now thanks!

[uzi4u2]

oka if we are on the topic of Alpha helix another small question

Which of the following Influence the stability of the alpha helix :

1. Adjacent amino acids with negatively charged side chains
2. Adjacent amino acids with bulky R groups
3. Adjacent amino acids with positively charged side chains
4. the accurance of prolin residues

i duno if its just me but i think all of them effect the stability , no ?


oo oo and also a small Km claculation :
What is the relative rate of the enzyme reaction when   S= 10 Km?
i'm sorry to shove all these questions its just that i have an exam tomorrow and the stress is killing me !

[Yggdrasil]

oka if we are on the topic of Alpha helix another small question

Which of the following Influence the stability of the alpha helix :

1. Adjacent amino acids with negatively charged side chains
2. Adjacent amino acids with bulky R groups
3. Adjacent amino acids with positively charged side chains
4. the accurance of prolin residues

i duno if its just me but i think all of them effect the stability , no ?

Yes, all of them affect the stability.  But it is important to know how the affect the stability (do they make the helix more stable or less stable) and why they affect the stability.

Here, it is important to think of how closely packed amino acids are in alpha helices versus other types of structures (e.g. beta sheets).

oo oo and also a small Km claculation :
What is the relative rate of the enzyme reaction when   S= 10 Km?
i'm sorry to shove all these questions its just that i have an exam tomorrow and the stress is killing me !

You should be able to get this simply by plugging into the Michaelis-Menten equation