Light-dependent reactions
The
light-dependent reactions, or
photoreduction, is the first stage of photosynthesis, is a process by which plants capture and store energy from sunlight. In this process, light energy is converted into chemical energy, in the form of the energy-carrying molecules ATP and NADPH. In the
light-independent reactions, the formed NADPH and ATP drive the reduction of CO 2 to more useful organic compounds, such as glucose. However, although light-independent reactions are, by convention, also called
dark reactions, they are not independent of the need of light, for they are driven by ATP and NADPH, products of light. They are often called the Calvin Cycle or C3 Cycle. The light-dependent reactions take place on the thylakoid membranes. The inside of the thylakoid membrane is called the lumen, and outside the thylakoid membrane is the stroma, where the light-independent reactions take place. The thylakoid membrane contains some integral membrane protein complexes that catalyze the light reactions. There are four major protein complexes in the thylakoid membrane: Photosystem II, Cytochrome b6f complex, Photosystem I, and ATP synthase.