Questions to elementary biochemistry

[strikken]

I'm new here..so hello everyone! *Smiling*

 

I'm a first year student with some questions to biochemistry, trying to understand this to the spring exam. I'm from Scandinavia and not that good in English..but I'll hope this is somewhat understandable and clear.

 

1. Enzymes doesn't influence equibrilium, but they lower the activation energy. I wonder how this is possible? Isn't the activation energy expressed in free Gibbs energy? If so, how can the equibrilium be unchanged? I thought delta Gibbs was the same as the distance to equibrilium. Or are we maybe talking about different delta Gs?

 

2. Under ATP synthesis the enzym ATP synthase undergoes rotational catalysis. I understand that something is rotated, but I don't understand what. Is it a change in the seat themselves, or do they only change places among eachother?

 

3. Under starvation keton bodies can deliver energy to the brain. Ok enough that the brain can make AcCoA from the keton body acetoacetate, but how can AcCoA give energy further through oxidation in the citric acid cycle? I thought that there was a lack of intermediates in the citric acid cycle under starvation, to use the intermediates to build up as much sugar as possible, unless this situation only occurs in the liver. Comments appreciated.

 

4. How can insulin stimulate the degradation of proteins? I cannot see the logic in this statement, because, as far I can see, this will lead to a less effective removal of blood glucose as pyruvate and AcCoa from glucose will get competition from the same degradation products from proteins.

 

5. In a class the teacher mentioned something called telomers, important to prolong a DNA thread at the end of a DNA molecule so that a primer can be synthisized to complete the last part of the lagging strand. Fair enough that the laggging strand at the end of a DNA molecule lacks a place to attach a RNA primer, but I'm not totally sure where the telomer is attached. After my opinion, this has to be from the 5'-end of the "old" DNA strand (the template strand for the new lagging strand), is this right?

 

 

I also wonder: is the only reason that we have thymine instead of uracil in DNA, that we can see if a deamination from cytosin has occurred?

Edited December 30, 2010 by strikken

[mississippichem]

I'm new here..so hello everyone! *Smiling*

 

I'm a first year student with some questions to biochemistry, trying to understand this to the spring exam. I'm from Scandinavia and not that good in English..but I'll hope this is somewhat understandable and clear.

 

1. Enzymes doesn't influence equibrilium, but they lower the activation energy. I wonder how this is possible? Isn't the activation energy expressed in free Gibbs energy? If so, how can the equibrilium be unchanged? I thought delta Gibbs was the same as the distance to equibrilium. Or are we maybe talking about different delta Gs?

 

Gibbs in related to the other thermodynamic state variables by:

 

[math]\Delta G^{o}={\Delta H^{o}}-{{T}\Delta S^{o}}[/math]

 

Gibbs energy is related to equilibrium by:

 

[math] \ln \left( {\frac{{K_2 }}{{K_1 }}} \right) = \frac{{ \Delta H^{o} }}{R}\left( {\frac{1}{{T_1 }} - \frac{1}{{T_2 }}} \right) [/math]

 

and

 

[math] \Delta G^\circ = -RT(\ln K) [/math]

 

Enzymes are catalysts, they just lower the activation barrier for a given reaction. This just lowers the "energy hump" on the reaction coordinate. No effect on equilibrium though. Activation barriers can be expressed in Gibbs, but those are Gibbs activation energies; different from the overall Gibbs energy for a reaction (the above math). It's easy to get confused about enzymes affecting equilibrium, they don't though.

 

Gibbs energy of activation is not equilibrium dependent:

 

[math]k = \frac{k_BT}{h}e^{-\frac{\Delta G_{act}}{RT}} [/math]

 

where the lower case k is the rate constant.

Edited December 30, 2010 by mississippichem

[strikken]

Thank you so much!

[Blahah]

2. Under ATP synthesis the enzym ATP synthase undergoes rotational catalysis. I understand that something is rotated, but I don't understand what. Is it a change in the seat themselves, or do they only change places among eachother?

 

The gamma subunit and the attached c subunit of ATP synthase rotate in between the alpha and beta subunits. In the diagram below, gamma is yellow, c is red and the alpha and beta subunits are the greenish parts at the top. The whole yellow and red part rotates driven by the flow of protons down the gradient. You can see the path of protons in the diagram.

edit: source of diagram is here... http://www.life.illinois.edu/crofts/bioph354/lect10.html

you can read more detail about ATP synthase at that site.

Edited February 12, 2011 by Blahah