Re: What are ATP and NADPH?

Dear Albie, Your question is very focused and at the same time very broad !!! I will try to be as general as possible. Let’s begin with ATP. We all know that living things (plants and animals) require a continual supply of energy in order to function. This energy is used for all the processes which keep the organism alive and is obtained mainly through the food that is absorbed. However, before the energy can be used, it has to be transformed by a complex process into ATP (a form which the organism can handle easily). The acronym ATP stands for adenosine triphosphate. You can see a picture of this useful molecule at : http://www.people.virginia.edu/~rjh9u/atpstruc.html.

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.
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).

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.