During the Light Dependent Reactions, activity occurs within the thylakoids of the chloroplast. NADP+ accepts two high energy electrons and an H+ ion and then converts into NADPH. This process ultimately traps some of the sunlight in chemical form. Then, NADPH is able to carry the energy it absorbs to the rest of the cell. The reaction produces O2 gas and converts ADP to ATP and NADP+ to NADPH. First, pigments in Photosystem II absorb light, which is then absorbed by electrons, which are then passed along the Electron Transport Chain. Chlorophyll loses an electron, but interestingly, those missing electrons are replaced through enzymes in the thylakoid membrane, which divide H20. Secondly, electrons move through the Electron Transport Chain from PII to PI and an H+ ion moves from the stroma to the inner thylakoid space. Thirdly, pigments from PI use energy from light to reenergize electrons; NADP+ picks them up along with H+ ions in the outer surface of the thylakoid, making NADPH. Next, as the electrons pass from chlorophyll to NADP+, more H+ ions are being pumped through the membrane to the inside of the thylakoid, which accounts for the inside being positive and the outside being negative. Lastly, ATP synthase, which spans the membrane, allows the H+ ions to go through it. As they go through, the synthase spins and rotates and binds an ADP to a phosphate group, producing ATP.
Specifically, the Light Reactions can either follow a noncyclic electron pathway or a cyclic electron pathway. During the noncyclic electron pathway, PII absorbs solar energy, which is passed along pigments until it is concentrated in a particular pair of chlorophyll a molecules, called the reaction center. Here, the electrons become very energized that they escape and go to electron acceptor molecules. The electron acceptor sends electrons down the ETC and ATP production occurs when they flow their gradient in ATP synthase. PI absorbs solar energy, but the...
Please join StudyMode to read the full document