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Topic: enthalpy  (Read 5201 times)

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« on: May 06, 2005, 08:42:39 PM »
I've been reading in texts that energy is released when bonds are formed and energy is absorbed when bonds are broken. I always thought the case was the other way around. When an ATP molecule is formed energy when into forming the high energy phosphate bond and so therefore wouldn't energy be absorbed. I am confused by this energy absorbed / released when bonds are formed/broken.  ???

Offline Donaldson Tan

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« Reply #1 on: May 06, 2005, 09:58:49 PM »
ATP -> ADP + iP + energy
One of the C-P bond in Adenosine Tri-Phospate (ATP) is broken to release energy for your muscles to work. The product is inorganic phosphate (iP) and adenosince diphosphate (ADP). Typically. the phosphate is absorbed by creatine in our body.

Normally, when we consume glucose, glucose is converted to ATP. Directly harnessing energy from gluocose isnt bad. You can see the effects of high glucose level in diabetics, especially their susceptibility to bacterial infection. Moreover, gluocose exert more osmotic pressure than ATP, so it would mean more work for our cells to maintain water content in them.

The concentration of ATP in our body isnt very high, but it's maintained at steady state because the approximately, the rate of ATP consumption equals the rate of ATP generation. Our body makes ATP by adding a phosphate to ADP through a different process. First, an enzyme release iP from one of the creatine-phosphate molecules, then energy from oxidising glucose is used to make the C-P bond to join the phospate to ADP to form ATP, ie.
Creatine-iP -> Creatine + iP
ADP + iP -> ATP

you may read up on krebs' cycle if you would like to know more.

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« Reply #2 on: May 07, 2005, 01:10:04 AM »
Just some added points to think about

ATP can be produced from a phosphorylation (substrate level) & chemiosmosis (oxidative phosphorylation).  Citric acid cycle (Krebs) produces only a little ATP - substrate.  ETC - electron transport chain, produces the most  30+ (varies) from the electron carriers reduced in the citric acid cycle.  

There has been a trend in biology to push the idea of coupled reactions more than this idea of "energy."  I was taught that ATP yields ADP & Pi along with energy.  The hydrolysis of the 2nd and 3rd phosphate groups release energy for cellular work and chemical synthesis.  The reactions happen so fast that the Pi gets picked up by a kinase and pushes another reaction.  I guess the trend might be leading to saying that ATP yields ADP & Pi along with another reaction.

I don't know, I keep teaching it as releasing energy.  The bond broken is sometimes described as a high-energy bond.  It's just a regular covalent bond, but in an aqueous environment ADP & Pi have lower energy.

I apologize if this provides no greater understanding in this topic.  It's late and I'm tired.

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