Chemical Structure of

  Biologically Important Compounds


  


 This page gives the chemical structures of several molecules
 commonly encountered in biological processes (particularly the
 Kreb's cycle).  The structures of all of these molecules contain
 the same adenosine nucleotide core:

   

     Base: Adenine
   

     Sugar: Ribose
   

     Phosphate: PO4 group on Carbon-5 of ribose.


 The molecules included on this page are:

   

     ATP
   

     NAD+ & NADH
   

     FAD & FADH2
   

     Coenzyme-A (CoA-SH)


  


  ATP


Adenosine triphosphate is a molecule commonly
used by the body to provide energy. Formally, the energy comes from the following
hydrolysis reaction, which produces the
diphosphate (ADP). Note that "free" phosphate is also
produced. Typically, the actual reactions used in biological processes are
phosphorylation reactions, where a phosphate group is transfered from
ATP to another compound.

ATP-4 + H2O ¾®
ADP-3 + HPO4-2 + H+

ATP + H2O ¾® ADP +
Pi + H+

DG = -7.3 kcal/mole





  NAD


The interconversion of nicotinamide adenine
dinucleotide between the reduced (NADH) and oxidized
(NAD+) forms is a common reaction in biological redox
(oxidation-reduction) reactions. Two electrons are transferred in the reaction.
The NADH produced by the Kreb's cycle is oxidized by the respiratory cycle
to produce 3 equivalents of ATP. In many anabolism reactions, the structurally
similar NADPH/NADP+ redox couple is used.

NADH-2 ¾® NAD-1
+ H+ + 2e-

NADH ¾® NAD+ + H+
+ 2e-





  FAD


The interconversion of Flavin adenine
dinucleotide between the reduced (FADH2) and oxidized
(FAD) forms is an alternative to the NADH/NAD+ couple in biological
redox (oxidation-reduction) reactions. Two electrons are transferred in the
reaction. One important difference between these two couples is that the
FADH2 produced by the Kreb's cycle is oxidized by the respiratory
cycle to produce only 2 equivalents of ATP.

FADH2-2 ¾®
FAD-2 + 2H+ + 2e-

FADH2 ¾® FAD + 2H+
+ 2e-





  Coenzyme A


Coenzyme-A (CoA) is an important catalyst for the activation of organic
molecules. Perhaps the most commonly encountered example of this reactivity
is in the activation of pyruvate to acetyl-CoA, used in preparation for the
Kreb's cycle. The key feature of this reaction is the conversion of the
carboxylate group of pyruvate into a high-energy thio-ester.

pyruvate- + NAD+ + CoA-SH
¾® acetyl-CoA + CO2 + NADH
+ H+





  


Last modified March 17, 1997

Kent State University - Stark Campus

Department of Chemistry

This Page Written and Maintained by

 Dr. Clarke Earley

email:
cearley@stark.kent.edu