MadSci Network: Biochemistry |
Dear Albie,
ATP is a member of a group of organic compounds containing phosphate groups
that are linked by means of “energy rich” chemical bonds. When this bond is
broken (giving adenosine diphosphate and inorganic phosphate), about 7.2
Calories of energy is made available to do work. However, when the organism
is resting and energy is not immediately needed, the reverse reaction takes
place (the phosphate group is reattached to the molecule). Thus the ATP
molecule acts as a rechargeable ‘chemical battery’, storing energy when it
is not needed, but able to release it instantly when the organism requires
it. At last, I have to tell you here that there is often a misbelief about
the “high-energy bond” of ATP. In fact, the energy is coming from the whole
molecule, that is the equilibrium between ATP and ADP + Pi, and not from
that particular bond.
Now, let’s talk about NADPH (Nicotinamide Adenine Dinucleotide Phosphate
Hydrogen). This molecule is very important in the life cycle of any cell (go
to this link to see what it looks like:
http://
www.bio.davidson.edu/Biology/Courses/Bio111/NADPH.html.
Undoubtedly, ATP and NADPH are essentials for the maintenance of the
chemistry of the cell. I hope that I have answer most of your questions.
Daniel.
Try the links in the MadSci Library for more information on Biochemistry.
In fact, a lot of reductive biosynthesis reactions require NADPH as an
“electron donor”. You can see some examples of reactions at this link:
http://www.med.unibs.it/~marchesi/ppp.html
Enzymes that function primarily in the “reductive direction” utilize the
NADP+/NADPH cofactor pair as co-factors. For example, the reactions of fatty
acid biosynthesis and steroid biosynthesis utilize large amounts of NADPH.
Another example is the conversion of ribonucleotides (RNA) to
deoxyribonucleotides (DNA) requires NADPH as the electron source, so that
any rapidly proliferating cell needs huge quantities of NADPH ! The NADPH is
mainly generated through the pentose phosphate pathway. This pathway
provides the cell with ribose-5-phosphate (r5P) for the synthesis of the
nucleotides (units of DNA).
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