NADPH stands for nicotinamide adenine dinucleotide phosphate hydrogen. This molecule plays a crucial role in some of the chemical reactions that make up the process of photosynthesis. NADPH is a product of the first stage of photosynthesis and is used to help fuel the reactions that take place in the second stage of photosynthesis. Plant cells need light energy, water and carbon dioxide to carry out the steps of photosynthesis.
TL;DR (Too Long; Didn't Read)
NADPH is an energy-carrying molecule produced in the first stage of photosynthesis. It provides energy to fuel the Calvin cycle in the second stage of photosynthesis.
The reactions in the first stage of photosynthesis require light in order to proceed. The main objective of this stage is to convert light energy from the sun into chemical energy. This stage of photosynthesis involves two sets of molecules known as photosystem I and photosystem II. The reactions of photosystem II happen first; it was named "II" because it was discovered after "I," but it occurs before "I" in the photosynthesis process. In this step, chlorophyll absorbs sunlight and transfers the energy to electrons. Next, the molecules of photosystem I also absorb sunlight, and the energy is added to the electrons to produce NADPH and ATP.
Electron Transport Chain
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. In photosystem I, the electrons are energized, and the energy is stored in molecules of NADP+. During these reactions, the NADP+ molecules are reduced by the addition of electrons. A hydrogen ion is added to NADP+ to form NADPH.
The Calvin Cycle
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. The NADPH produced in the light-dependent stage of photosynthesis provides the chemical energy to fuel the Calvin cycle and keep it going.
NADPH vs. ATP
Adenosine triphosphate, or ATP, is another molecule produced when light energy is converted to chemical energy via the electron transport chain. Like NADPH, it also provides energy that chloroplasts use to make sugar from carbon dioxide. ATP forms when a phosphate group is added to ADP, adenosine diphosphate, in a process called photophosphorylation. The hydrogen ions freed by the breakdown of water molecules flow through an enzyme called ATP synthase. This enzyme catalyzes the reaction that adds a phosphate group to ADP, producing ATP.