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Name: Lance
Status: Student
Age: 15
Location: N/A
Country: N/A
Date: N/A 


Question:
About my last question pertaining to the energy of cells set at 300 millivolts, this is the website I saw it on:

http://www.gla.ac.uk/publications/leadingedge/5/3.html.

The website says that the energy present around the membrane of a cell is around 300 millivolts. Anyways, here is my new question: How, exactly, does ATP provide energy to a cell?



Replies:
ATP is the abbreviation of Adenoside-tri-phosphate. The three phosphates are attached to the sugar component (a ribose bound to Adenosine) through high-energy bonds. Especially the third phosphate stores a lot of energy when bound to ADP. Releasing two phosphates from the sugar, results in AMP (Adenoside-mono-phosphate), inorganic phosphate, and energy.

ATP -> AMP + 2 PO4- + energy

It is this energy that can be passed on to other molecules, for instance to enable chemical reactions that are endotherm (require energy to take place).

ATP is the 'sugar lump' of a cell. It is an efficient way to temporary store energy that can quickly be released by one reaction. The energy is stored in the form of chemical bonds, but can be converted into electrical energy, into other chemical bonds, or into power (by contraction of muscle cells). In the case of cell membrane potential, it is ATP that drives ion pumps (complex proteins that span the membrane) to restore an electrical potential.

I hope this answers your question in sufficent detail.

Trudy Wassenaar


A cell membrane potential of 300 millivolts. Yes, that makes much more sense that an energy of 300 milliwatts. You see, volts (or millivolts) is not a unit of energy, but of electrical potential. Potentials don't add together like energies; 100 trillion cells at 300 mV each is still a potential of only 300 mV. The potential defines the energy of a separated charge across some boundary, in units of joules/coulomb.

The answer to your new question is very complicated and not fully understood. Many different proteins extract energy from the hydrolysis of ATP. All of them appear to couple some sort of motion of the protein with the energy-releasing hydrolysis. The motion of the protein can in turn be harnessed to do necessary things, such as pump chemicals across a cell membrane (which is how the 300 mV membrane potential arises), move the cell around, synthesize new proteins, and so on.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois



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