For this video project, we decided to explore the process of photophosphorylation Photophosphorylation is the process by which ATP is created during the light-dependent phase of photosynthesis in plants. Photophosphorylation begins when a photon of light corresponding to a red-orange or green-blue frequency hits the chlorophyll in the chloroplast of a plant. That energy from the photon excites an electron in the chlorophyll, causing it to leave the chlorophyll. The chlorophyll, having become oxidized, requires a new electron. The accessory protein in the thylakoid membrane pulls an electron from one of the many water molecules in the stroma, and passes it back to the chlorophyll. The water molecule, having lost an electron, breaks down into two hydrogen ions and one oxygen molecule. The freed oxygen molecules bond together, forming O2, and leave the plant entirely. The electron that was originally released from the chlorophyll gets passed to the cytochrome. This excites the cytochrome, causing it to pump the newly freed hydrogen ions from the stroma, through the thylakoid membrane and into the thylakoid space. The large concentration of hydrogen ion forms a chemiosmotic gradient. The hydrogen ions, compelled by the laws of diffusion, must leave the thylakoid space so they move through the ATP synthase enzyme. The momentum produced from the mass exodus of hydrogen ion spins the ATP synthase. The ATP synthase is attached to an ADP molecule, and one phosphate group. The spinning motion bonds the ADP with the phosphate group forming ATP, the final product of the photophosphorylation reaction. By Afra K. and Angie T.

Photosynthesis takes the human/animal waste product carbon-dioxide (CO2) and in the presence of light and water creates the things we need for cellular respiration, oxygen and glucose. See the following links: Cellular Respiration - http://www.youtube.com/watch?v=OqSnts1C_0g Calvin Cycle - http://www.youtube.com/watch?v=VFp-4vo6Ch8 Light and Pigments - http://www.youtube.com/watch?v=OUUsKXR27rs The initial stage of the photosynthetic system is the light-dependent reactions, which convert light -solar energy- into chemical (potential) energy. The light dependent reactions specifically produce oxygen gas and convert ADP into ATP and NADP+ into NADPH. Organisms form the kingdom Plantae usually use noncyclic(do not reCYCLE same electrons) photophosphorylation, a two-stage process involving two different chlorophyll photosystems. First, light strikes a plant, specifically a cell. This cell has an organelle(s) called a chloroplast that gives photosynthetic cells their characteristic green color. Chloroplasts have structures called stroma. Stroma are full of hollow disks (similar to a whoopie cushion) called thylakoids arranged in stacks call grana. There are membrane proteins implanted into the surface of the thylakoid called photosystem II and photosystem I that have a pigment called chlorophyll located on the top of these proteins.***Photo System I comes second, but was discovered first and Photo System II was found second and named for that reason even though it comes first.*** Light particles, called photons, strike the electrons located in the chlorophyll of photo system II, Now in an excited state, they travel along the thylakoid membrane to photo system I where they are re-excited by photons again moving them to the acceptor molecule NADP+. The flow of electrons through the membrane proteins creates a concentration gradient, also known as proton motive force, which drives ATP synthesis through chemiosmosis (see http://www.youtube.com/watch?v=Btl0ltsw4m0). The electrons originally lost in Photo System II must be replaced. A water molecule is broken down into 2H+ + 1/2 O2 + 2e- by a process called photolysis (or light-splitting). The two electrons from the water molecule replenish electrons lost in photosystem II's chlorophyll. Meanwhile the 2H+ and 1/2O2 are left out for further use. The photosystem II complex replaced its lost electrons from an external source, however, the two other electrons are not returned to photosystem II as they are in the analogous cyclic pathway(prokaryotes like cyanobacteria). The highly excited electrons are transferred to the acceptor molecule, but this time are passed on to an enzyme called Ferredoxin- NADP reductase(NADP+ reductase), for short FNR, which uses them to catalyze the following reaction (as shown): NADP+ + 2H+ + 2e- → NADPH + H+ This consumes the H+ ions produced by the splitting of water, leading to a net production of 1/2O2, ATP, and NADPH+H+ with the consumption of the light(photons) and water. Next are the dark reactions(not light dependant)... The Calvin Cycle - http://www.youtube.com/watch?v=VFp-4vo6Ch8

Photosynthesis is the only process that converts light energy into chemical energy. The light dependent reaction, which is the concentration of this video, occurs in the chloroplasts of a leaf. This reaction is initiated by a photon of light, and goes through several steps such as: photolysis of water, excitement of the cytochrome, and pumping of protons from the stroma into the thylakoid space. In result of the previous steps, protons start to accumulate in the thylakoid space making its pH acidic. In fact when the ATP synthase senses the pH of 5, a small tube opens in the complex protein structure, and passive transport of protons from the thylakoid membrane out to the stroma occurs. These protons move through the ATP synthase at a high speed carrying with them an enormous amount of energy, it is this energy that is used to create molecules of ATP through the process of photophosphorylation.

Video Cam Direct Upload Genes don't "make" organisms. http://www.imbf.ku.dk/MolBioPages/abk/PersonalPages/Jesper/Basel.html "The ordinary textbook talk of DNA as governing cellular or even organismic behavior is therefore rather misleading. In fact if any entity should be thought of as a governor of cellular activity this should certainly be the membrane. DNA contains the recipes for constructing the one-dimensional amino acid chains, which form the backbones of enzymes, and among them the enzymes needed for catalyzing the formation of the constituents of lipid bilayers and assembling them. But whether these recipes are actually 'read' and executed by cellular effectors depends on membrane bound activity. All major activities of cells are topologically connected to membranes. In the prokaryotes (bacteria) the plasma membrane (the active membrane inside the cell wall) is itself in charge of molecular and ionic transport, biosynthetic translocations (of proteins, glycosides etc.), assembly of lipids, communication (via receptors), electron transport and coupled phosphorylation, photoreduction photophosphorylation, and anchoring of the chromosome (replication) (de Duve 1991). In eukaryotic cells these tasks has been taken over by specific subcellular membrane structures of mitochondria, chloroplasts, the nuclear envelope, the Golgi apparatus, ribosomes, lysozomes etc. Many - if not all - of these membranes are themselves descendants from once free living prokaryotic membranes which perhaps a billion years ago became integrated into that co-operative or symbiotic complex of prokaryotic membranes which is the eukaryotic cell. Membranes also are the primary organizers of multi-cellular life. The topological specifications necessary for growth and development of a multi-cellular organism cannot be derived from the DNA for the good reason that the DNA cannot 'know' where in the organism it is located. Such 'knowledge' has to be furnished through the communicative surfaces of the cells. Morphogenesis is mostly a result of local cell-cell interactions in which signaling molecules from one cell affect neighboring cells. Animal cells, for instance, are constantly exploring their environments by means of little cytoplasmic feelers called filopedia (filamentous feet) that extend out from the cell. 'These cytoplasmic extensions that drive cell movement and exploration are expressions of the dynamic activity of the cytoskeleton with its microfilaments and microtubules that are constantly forming and collapsing (polymerizing and depolymerizing), contracting and expanding under the action of calcium and stress' writes Brian Goodwin(Goodwin 1995):36). But not only are membranes involved in all the organized activities of the life sphere, the membrane can actually be seen as the principal locus for life itself (Hoffmeyer 1998b; Hoffmeyer 2000b)[8]. It's the membrane that creates the potential inside-outside asymmetry from which the organism-environment asymmetry must have grown out. The origin of life is by necessity also the origin of the environment, and lack of concern for this aspect of the origin problem has seriously hampered much theorizing on prebiotic evolution. Somehow the world became divided into organism and environment, and the formation of a closed membrane must have been part of this process. Here the membrane not only assures the necessary topological closure, but more significantly it takes on the role of an interface facilitating a flow of messages between its interior and exterior domains. Considered from the point of view of the membrane prebiotic evolution is essentially a process of "interiorisation" (Hoffmeyer 2000b). Prebiotic membranes colonized the interior space and thereby scaffolded themselves through the formation of a multitude of autocatalytic metabolic loops and finally of replicative molecules mapping constituents of the internal autocatalytic system. Thus persistent architectures appeared as entities engaged in the trick of conjuring up a virtual reality at the inside for the purpose of coping effectively with the outsides. On the background of this discussion it might be fruitful to introduce the term the extended membrane as the inner locus for life. The extended membrane encompasses the totality of membranes that make up an organism (including its skin, plumage, etc.) and is responsible for the actual execution of life as process, semiotic agency. It is the extended membrane that directs ontogeny in a selforganized process scaffolded by an internal system of 'labels', genes, kept orderly in the genome."

Biochemistry VI (cont.) DNA as Genetic Material (Prof. Graham Walker) View the complete course: http://ocw.mit.edu/7-014S05 License: Creative Commons BY-NC-SA More information at http://ocw.mit.edu/terms More courses at http://ocw.mit.edu