Bio chemistry test tomorrow a little confused by some topics please help!!! asap

Question

Ok I am studying for my biochemistry exam for tomorrow and when I was looking at the review sheet I was a little thrown off by a couple of topics and I wasn't sure if someone could please explain them to me:

1) Be able to recognize the gen features of metabolic pathways. This would include the ways in which pathways are regulated (reactants and products, allosteric, covalent, synthesis degradation, and be able to know whiare fastest and slowest and how reactions are coupled.

2) Be able to explain why ADP and AMP levels are more sensitive as allosteric effectors than ATP.

3) 2 ways n which energetically unfavorable reactions are made to proceed in pathways.

Ok honestly the section on metabolism which all three are from has me very confused. I was not sure what to do with any of these three. I know this will be on teh test tomorrow and I've read the chapter 3 times and looked at notes I just need someone to maybe explain in better terms in a way I may follow. I honestly am confused by allosteric it keeps saying that but I'm not even sure what that means please help I really need it thank you

Answer 1

I just wrote a biochemistry exam today.  I wish you all the best on yours tomorrow!  Hopefully this will help a little:

1)  I don't see this being a question I can help you with, more of something you'll have to remember based on what pathways you've studied.

2) ADP + ADP --> ATP + AMP (reversible reaction)

Remember that the total adenylate pool (AMP,ADP,AMP) is constant (at least over a short time frame) and and the concentration of ADP is, in turn, greater than that of AMP.  Therefore, small changes in ATP concentration percentages result in larger changes in ADP and AMP concentration percentages.  This magnification of changes (especially from ATP to AMP) leads to tighter control by increasing the range of sensitivity of the enzyme (i.e. phosphofructokinase in glycolysis)

3) Energetically unfavorable reactions are made to proceed in pathways by coupling them to energetically favorable ones.  ATP is the most common example.  The breaking of the phosphate bond provides energy to force the counterpart (the unfavorable part) forward.  Another example is the movement of a proton across a membrane with it's gradient.  This reaction can couple with the movement of another particle (inorganic phosphate for example) to move the other particle even though the movement on its own would be unfavorable.