Where is nadp reduced

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Recall that during CR, the energy carried by NADH and FADH2 is used to pump protons across the inner mitochondrial membrane and into the intermembrane space, creating an electrochemical proton gradient.

The energy that these molecules carry is stored in a bond that holds a single atom to the molecule. Recall that NADH was a similar molecule that carried energy in the mitochondrion from the citric acid cycle to the electron transport chain. This potential energy is harvested and stored as chemical energy in ATP through chemiosmosis, the movement of hydrogen ions down their electrochemical gradient through the transmembrane enzyme ATP synthase, just as in the mitochondrion.

The hydrogen ions are allowed to pass through the thylakoid membrane through an embedded protein complex called ATP synthase. The energy generated by the hydrogen ion stream allows ATP synthase to attach a third phosphate to ADP, which forms a molecule of ATP in a process called photophosphorylation.

The flow of hydrogen ions through ATP synthase is called chemiosmosis just like in cellular respiration , because the ions move from an area of high to low concentration through a semi-permeable structure. The remaining function of the light-dependent reaction is to generate the other energy-carrier molecule, NADPH. As the electron from the electron transport chain arrives at photosystem I, it is re-energized with another photon captured by chlorophyll.

Now that the solar energy is stored in energy carriers, it can be used to make a sugar molecule. The pigments of the first part of photosynthesis, the light-dependent reactions, absorb energy from sunlight. A photon strikes the antenna pigments of photosystem II to initiate photosynthesis. The energy travels to the reaction center that contains chlorophyll a to the electron transport chain, which pumps hydrogen ions into the thylakoid interior the lumen.

In this step, chlorophyll absorbs sunlight and transfers the energy to electrons. In photosystem II, chlorophyll within the chloroplasts of plant cells absorbs sunlight and transfers the energy to electrons. The electrons undergo a series of reactions as they are transferred from one protein to another in an electron transport chain.

The light-dependent reactions break down water molecules, separating into hydrogen ions, oxygen molecules and electrons. Hydrogen ions are transported with the electrons along the chain of reactions.

The second stage of photosynthesis uses carbon dioxide to produce molecules of glucose. These reactions do not need light energy to proceed and are sometimes called the light-independent reactions.

The Calvin cycle adds one molecule of carbon dioxide at a time, so it must repeat to synthesize the six-carbon structure of glucose. Both of these coenzymes play crucial roles in this. However, only one proton accompanies the reduction. The other proton produced as two hydrogen atoms are removed from the molecule being oxidized is liberated into the surrounding medium.