light reactions occur at thylakoid membranes in the chloroplast.
where do the light reactions occur in the chloroplast?
thylakoid membranes
section::::function and chemistry.:photosynthesis.:light reactions.





























the light reactions take place on the thylakoid membranes. they take light energy and store it in nadph, a form of nadp, and atp to fuel the dark reactions.





























section::::function and chemistry.:photosynthesis.:light reactions.:energy carriers.





























atp is the phosphorylated version of adenosine diphosphate (adp), which stores energy in a cell and powers most cellular activities. atp is the energized form, while adp is the (partially) depleted form. nadp is an electron carrier which ferries high energy electrons. in the light reactions, it gets reduced, meaning it picks up electrons, becoming nadph.





























section::::function and chemistry.:photosynthesis.:light reactions.:photophosphorylation.
chloroplast
in addition to regulation at the longer time scale by means of expression control, regulation at the short-time scale can occur through allosteric mechanisms. c nadp-me has been shown to be partially inhibited by its substrate, malate, suggesting two independent binding sites: one at the active site and one at an allosteric site. however, the inhibitory effect exhibits ph-dependence – existent at a ph of 7 but not a ph of 8. the control of enzyme activity due to ph changes align with the hypothesis that nadp-me is most active while photosynthesis is in progress: active light reactions leads to a rise in basicity within the chloroplast stroma, the location of nadp-me, leading to a diminished inhibitory effect of malate on nadp-me and thereby promoting a more active state. conversely, slowed light reactions leads to a rise in acidity within the stroma, promoting the inhibition of nadp-me by malate. because the high energy products of the light reactions, nadph and atp, are required for the calvin cycle to proceed, a buildup of co without them is not useful, explaining the need for the regulatory mechanism.
malate dehydrogenase (oxaloacetate-decarboxylating) (nadp+)