o, organisms that do not have a full cycle can still make the 4 key metabolic precursors by using previously extracted energy and electrons (ATP and NADH) to drive some key steps in reverse.
I imagine this is not favorable? If the energy is needed for growth and development the fact they have to recycle a portion of it to create more ATP means that their growth is limited to some degree. Is it mainly unicellular and tiny microorganisms that do not have a full 4 key metabolic precursors.
This step is considered irreversible because it is so highly exergonic.
Meaning that the reverse reaction would be too endergonic that there is either insufficient energy to provide for the reverse reaction or mechanisms deem it a waste of energy and would work out different solutions?
he resulting acetyl-CoA can enter several pathways for the biosynthesis of larger molecules or it can flow into another pathway of central metabolism called the Citric Acid Cycle, sometimes also called the Krebs Cycle, or Tricarboxylic Acid (TCA) Cycle.
I learned this in a lot of detail in IB Bio and when I was going through dissecting steps, I remember at some points there were random H+ coming into the mix and I did not understand where they were coming from because I thought of this process as being isolated. Right now, I am thinking that these H+ probably exist within the environment that the reaction is taking place within and are simply grabbed up?
As the ATP is consumed, the muscle cells are unable to keep up with the demand for respiration, O2 becomes limiting, and NADH accumulates. Cells need to get rid of the excess and regenerate NAD+, so pyruvate serves as an electron acceptor, generating lactate and oxidizing NADH to NAD+. Many bacteria use this pathway as a way to complete the NADH/NAD+ cycle.
Slightly unrelated to the topic at hand but did this evolve in species after they started becoming more physically active? I wouldn't think that bacteria would have any use for this pathway within this specific context (generating lactic acid to meet demand for energy due to exercise). Also how important is the production of lactic acid; does the acid itself have benefits or is it simply a byproduct/tradeoff?
A variety of mechanisms have emerged over the 3.25 billion years of evolution to create ATP from ADP and AMP
I think this is implying that ADP came first and then ATP evolved from ADP but this leads me to think about how ADP came into existence. I dont think its a case similar to the phospholipid bilayer where it just happens if theres enough of the needed molecules floating around and without ATP which is what releases energy after turning into ADP, I don't understand its function or importance in organisms before
Can you state what you know so far about the relationship between NADH/NAD+ and ATP?
I remember from my high school biology that NADH is an electron carrier that carries the electrons to the transport chain at the very end. On the other hand, ATP turning into ADP should be releasing energy that is used to go against a gradient. I don't remember exactly but I think there is a pump in the membrane related to ATP that uses it to pump H+
The hydrolysis reactions that liberate one or more of ATP's phosphates are exergonic
This is what I have been so confused about. In chemistry I've learned that it takes energy to break bonds so the reactions that involve the breaking of bonds are endothermic but then that challenged my idea that liberating a phosphate is an exergonic process. I don't understand how these ideas co-exist. Is it that the ATP into ADP is happening at a bigger scale than the chemistry I am talking about so it is not as relevant?