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NADP: Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5'-phosphate (Nmn) coupled by pyrophosphate linkage to the 5'-phosphate adenosine 2',5'-bisphosphate. It serves as an electron carrier in a number of reactions, being alternately oxidized (Nadp+) and reduced (Nadph). (Dorland, 27th ed)

The Calvin Cycle

JoVE 10753

Oxygenic photosynthesis converts approximately 200 billion tons of carbon dioxide (CO2) annually to organic compounds and produces approximately 140 billion tons of atmospheric oxygen (O2). Photosynthesis is the basis of all human food and oxygen needs.

The photosynthetic process can be divided into two sets of reactions that take place in different regions of plant chloroplasts: the light-dependent reaction and the light-independent or “dark” reactions. The light-dependent reaction takes place in the thylakoid membrane of the chloroplast. It converts light energy to chemical energy, stored as ATP and NADPH. This energy is then utilized in the stroma region of the chloroplast, to reduce atmospheric carbon dioxide into complex carbohydrates through the light-independent reactions of the Calvin-Benson cycle. The Calvin-Benson cycle represents the light-independent set of photosynthetic reactions. It uses the adenosine triphosphate (ATP) and nicotinamide-adenine dinucleotide phosphate (NADPH) generated during the light-dependent reactions to convert atmospheric CO2 into complex carbohydrates. The Calvin-Benson cycle also regenerates adenosine diphosphate (ADP) and NADP+ for the light-dependent reaction. At the start of the Calvin-Benson cycle, atmospheric CO2 enters the leaf throug

 Core: Biology

Photosystem I

JoVE 10752

Like Photosystem II (PS II), Photosystem I (PS I) captures photons and transports them through chlorophyll molecules into a reaction center. In PS I, the photons reenergize the electrons that have entered PS I from PS II. From the reaction center, the high energy electron is sent through an electron transport chain and ultimately joins with an additional electron and a proton to reduce NADP+ into NADPH. Thus, similar to PS II that captures energy to generate ATP, PS I captures energy to create NADPH. The pigments of the light-harvesting complex in Photosystem I absorb photons and relay the energy to the reaction center (P700). Following oxidation, a high-energy electron is passed from the specialized pair of chlorophyll a to the primary electron acceptor. This time, however, the missing electrons from the chlorophyll a pair are replaced by the electrons traveling from Photosystem II (instead of splitting of water as in PS II). On their way from PS II to PS I, the electrons pass through the electron transport chain, comprising the carrier molecule plastoquinone, the dual-protein cytochrome complex, and plastocyanin. Once the electron was excited in the reaction center of PS I, it enters a second electron transport chain—the protein complex ferredoxin. The single electron then joins with another electron and a proton (H+)

 Core: Biology

Anatomy of Chloroplasts

JoVE 10750

Green algae and plants, including green stems and unripe fruit, harbor chloroplasts—the vital organelles where photosynthesis takes place. In plants, the highest density of chloroplasts is found in the mesophyll cells of leaves.

A double membrane surrounds chloroplasts. The outer membrane faces the cytoplasm of the plant cell on one side and the intermembrane space of the chloroplast on the other. The inner membrane separates the narrow intermembrane space from the aqueous interior of the chloroplast, called the stroma. Within the stroma, another set of membranes form disk-shaped compartments—known as thylakoids. The interior of a thylakoid is called the thylakoid lumen. In most plant species, the thylakoids are interconnected and form stacks called grana. Embedded in the thylakoid membranes are multi-protein light-harvesting (or antenna) complexes. These complexes consist of proteins and pigments, such as chlorophyll, that capture light energy to perform the light-dependent reactions of photosynthesis. These processes release oxygen and produce chemical energy in the form of ATP and NADPH. The second part of photosynthesis—the Calvin cycle—is light-independent and takes place in the stroma of the chloroplast. The Calvin cycle captures CO2 and uses the ATP and NADPH to ultimately produce sugar.

 Core: Biology

Photosynthesis- Concept

JoVE 10565

Autotrophs

Almost all living organisms on Earth depend on photosynthesis, which is the process that converts sunlight energy into a simple sugar called glucose. This molecule can be used as a short-term energy source or to build more complex carbohydrates like starches for long-term energy storage. Autotrophs are organisms that capture light energy using photosynthesis. Also known …

 Lab Bio

What is Photosynthesis?

JoVE 10748

Photosynthesis is a multipart, biochemical process that occurs in plants as well as in some bacteria. It captures carbon dioxide and solar energy to produce glucose. Glucose stores chemical energy in the form of carbohydrates. The overall biochemical formula of photosynthesis is 6 CO2 + 6 H2O + Light energy → C6H12O6 + 6 O2. Photosynthesis releases oxygen into the atmosphere and is largely responsible for maintaining the Earth’s atmospheric oxygen content. Photosynthetic reactions occur in chloroplasts, specialized membrane-enclosed compartments in the plant cell. Chloroplasts consist of coin-like stacks of thylakoids. One such stack is called a granum. The thylakoid membranes are enriched with chlorophyll, a green pigment that gives plants and especially their leaves their green color. The chlorophyll molecule absorbs light energy in the form of photons from violet-blue, and orange and red wavelengths. The photons initiate a cascade that powers the reactions of Photosystem II and Photosystem I that produce ATP and NADPH. These two molecules are then used to power the light-independent reactions of the Calvin Cycle that take place in the stroma of the chloroplast to produce complex carbohydrates. Some plants, like corn and cacti that grow in dry, hot climates, use modi

 Core: Biology

Detecting Reactive Oxygen Species

JoVE 5654

Reactive oxygen species are chemically active, oxygen-derived molecules capable of oxidizing other molecules. Because of their reactive nature, there are many deleterious effects associated with unchecked ROS production, including structural damage to DNA and other biological molecules. However, ROS can also be mediators of physiological signaling. There is accumulating…

 Cell Biology

Imaging Approaches to Assessments of Toxicological Oxidative Stress Using Genetically-encoded Fluorogenic Sensors

1Department of Environmental Sciences and Engineering, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, 2Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, 3Oak Ridge Institute for Science and Education

JoVE 56945

 Cancer Research
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