Ask A Scientist© Molecular Biology Archive

name        Lance
status      other
age         15

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?

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
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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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It has potential energy stored in the three phosphate bonds  (adenine
tri-phosphate)...this potential energy is used to drive other reactions in
the body that would not otherwise occur at the rate needed.  It usually
involves a series of enzymes that help in the transfer of the high energy
phosphate from the ATP to the substrate...these enzymes (biological
catalysts) are called kinases.  The amount of energy released when
[ATP-->ADP+ PHO4~substrate] is about -30.5 kilojoules.mole-1 .  It is
customary to report favorable reactions with  a negative number.

PF
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