Glyceraldehyde 3-phosphate
Commonly abbreviated to
GALP, or occasionally
PGAL, this molecule is the 3-
carbon end-product of the
Calvin Cycle which takes place in the absence of light in the
stroma of any
photosynthetic cell of a plant. The stroma can be considered by analogy to be the
cytoplasm of a
chloroplast, but this is a huge simplification of course.
At the end of the
light dependent reaction small quantities of
adenosine triphosphate (ATP) and larger quantities of reduced hydrogen ion accepting
NADPH have been produced.
The
Calvin Cycle proceeds as follow (in only enough detail to illustrate GALP production):
- CO2 fixation with respect to ribulose biphosphate
- Cleaving of the RUBP molecule to form two 3-carbon gylcerate-3-phosphate
- Reduction of GP to GALP
It is this reduction step that requires the
NADPH. A
redox reaction is undertaken and the co-enzyme is oxidised to it's original form, thereby replenishing it's original supply. If supplies of
NADP (the non-reduced form of
NADPH) are exhausted, then the
light dependent reaction will grind to a halt, as otherwise
H+ produced would lower pH and cause enzyme
denaturation.
Experimentaly, 83% of the
GALP is used in the reformation of
RuBP - allowing cycling to continue. The remainder is used in the
synthesis of whatever the plant further requires. Usually the reaction pathway proceeds to
fructose, but additional methods are possible for synthesis of other
compounds.
GALP and it's key importance in the biochemistry of life was discovered in the famous
Calvins lollipop experiment, before which biologists had little idea as to what chemical was fulfilling such a vital role.
Biochemistry of photosynethsis and respiration is of course ridiculously complex and unlike Chemistry, Biology has yet to obtain a standardised chemical naming scheme (think
IUPAC), so YMMV when comparing this accross textbooks. If you want the full story in all it's glory, you're looking in the wrong place.