bio questions

[ramseszerg]

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ATP -> ADP releases energy and ADP -> ATP requires energy. Wouldn't it require energy to break a bond, and release energy to form it?

Also, why does Cliff's list allosteric enzyme and noncompetitive inhibition separately when there is no difference in the descriptions? (page 24)

Thanks.

 

[Ibracadabra]

ATP -> ADP releases energy and ADP -> ATP requires energy. Wouldn't it require energy to break a bond, and release energy to form it?

Also, why does Cliff's list allosteric enzyme and noncompetitive inhibition separately when there is no difference in the descriptions? (page 24)

Thanks.

For the first part, it's one thing that I was a bit curious on as well. I hope other SDNers can do a better job at explaining this. I personally thought that since phosphoanhydride bonds(2 of them b/w the 3 phosphates for an ATP molecule) are very reactive/high E bonds, they release E when they break and require E when they form. There are two phosphoanhydride bonds in an ATP molecule, and I believe that this is the reason why that ATP can be broken down into ADP or AMP(one p is still attached) in the cell, depending on the E requirement.

For Cliff's explanation, I felt the same way as you did.
There are two types of competitive inhibitors 1) reversible and 2) irreversible. Both types mimic the substrate and compete with the substrate for the active site--it only depends if they just stay there for a while and fall off or covalently bond with the active site permanently.

Non-competitive inhibitors bind to the allosteric sites of enzymes (a site other than the active site) and decrease the activity of the enzyme most likely by changing the conformation of the enzyme. This is non-competitive because it does not compete with the substrate for the active site.

I believe that there can also be allosteric activators(?) that binds to the allosteric site to enhance the enzymatic activity. For example, phosphofructokinase's(participates in glycolysis) allosteric inhibitor is ATP, while its activator is AMP or ADP. This can also be an example of negative feedback where the product of glycolysis--ATP--comes to slow down the process of glycolysis.

Hope it helps! 😀

 

[UCB05]

It's not like ATP just breaks a bond and loses a phosphate group. ATP gets hydrolyzed into ADP-H. The phosphate-phosphate bond is much less stable than the protonated bond left after hydrolysis, leading to a net release of energy when the phosphate group is hydrolyzed. Does that make more sense?

As far as why there is so much energy released, ATP is a very special molecule. The phosphodiester bonds are kinetically stable - they're unlikely to degrade. However, three phosphate groups in series cause a lot of electrostatic repulsion that makes the molecule thermodynamically unstable. This gives our cells a way to store chemical energy in a form that isn't likely to just explode on itself until the cell wants it to.

 

[Troyvdg]

It's not like ATP just breaks a bond and loses a phosphate group. ATP gets hydrolyzed into ADP-H. The phosphate-phosphate bond is much less stable than the protonated bond left after hydrolysis, leading to a net release of energy when the phosphate group is hydrolyzed. Does that make more sense?

As far as why there is so much energy released, ATP is a very special molecule. The phosphodiester bonds are kinetically stable - they're unlikely to degrade. However, three phosphate groups in series cause a lot of electrostatic repulsion that makes the molecule thermodynamically unstable. This gives our cells a way to store chemical energy in a form that isn't likely to just explode on itself until the cell wants it to.

continuing off of what you said, there's a lot of potential energy due to:

1. the three phosphates together have a lot of electrostatic repulsion
2. ADP + P can form more hydrogen bonds than ATP
3. ATP--> ADP + P increases entropy

So when it is hydrolyzed, it is a highly exergonic reaction