Compare and Contrast Photophosphorylation and Oxidative Phosphorylation?

Oxidative Phosphorylation
-------------------------------------
reduced NAD and reduced FAD are reoxidised when they donate hydrogen atoms, which are split into protons and electrons, to the electron carriers.

the first electron carrier to accept electrons from reduced NAD is a protein complex, complex I, called NADH - coenzyme Q reductase (NADH dehydrogenase)

the protons go into solution in the matrix
--------------------------------------…
as electrons flow along the ETC, energy is released and used, by coenzymes associated with some of the electron carriers (complexes I, III and IV), to pump protons across the intermembrane space.

this builds up a proton gradient and thus potential energy builds up in the intermembrane space

the hydrogen ions cannot diffuse through the lipid part of the inner membrane but can diffuse through the ion channels in it, these channels are associated with the enzyme ATP synthase. This flow of hydrogen ions is called CHEMIOSMOSIS
--------------------------------------…
as protons flow through and ATP synthase enzyme, they drive the rotation of part of the enzyme and join ADP adn Pi (inorganic phosphate) to form ATP.

the electrons are passed from the last carrier in the chain to molecular oxygen, which is the final electron acceptor
4H+ + 4e- + O2 -> 2H2O

26 molecules of ATP are produced by oxidative phosphorylation per glucose molecule + ATP from krebs and glycolysis ATP per glucose should be 30 molecules. However :
>some protons leak across mitochondrial membrane reducing number of protons to generate proton motive force
>some ATP produced is used to actively transport pyruvate into the mitochondria
>some ATP is used for the shuttle to bring hydrogen from reduced NAD made during glycolysis into the mitochondria



phew there's oxidative phosphorylation hope u can use this to compare it against whatever you get for photophosphorylation or whatever research or understanding you already have.

photophosphorylation
--------------------------------

when a photon hits a chlorophyll molecule the energy of the photon is transferred to 2 electrons and they become 'excited'. These electrons are captured by electron acceptors and passed along a series of electron carriers embedded in the thylakoid membranes. The electron carriers are protein that contain iron atoms.

Energy is released as electrons pass along the chain of electron carriers. this pumps protons across the thylakoid membranes into the thylakoid space where they accumulate. A proton gradient is formed across the thylakoid membrane and the protons flow down their gradient, through channels associated with ATP synthase enzymes. this flow of protons is called chemiosmosis. It produces a force that joins ADP to Pi to make ATP. the kinetic energy from the proton flow is converted to chemical energy in the ATP molecules, which is used in the light-independant stage of photosynthesis. The making of ATP using light energy is called photophosphorylation. there are 2 types - cyclic and noin-cyclic

Cyclic photophosphorylation
--------------------------------------…
this uses photosystem I (P700). The excited electrons pass to an acceptor and back to the chlorophyll molecule from which they were lost. there is no photolysis of water and no generation of reduced NADP, but smal amounts of ATP are made. This may be used in the light-independant reaction of photosynthesis or it may be used in guard cells (their chloroplasts only contain photosystem I) to bring in potassium (K) ions, lowering the water potential and causing water to follow by osmosis.

Non-cyclic photophosphorylation
--------------------------------------…
This involves both photosystems - PSI (P700) and PSII (P680)

1. Light strikes PSII, exciting a pair of electrons that leave the chlorophyll molecule from the primary pigment reaction centre.
2. The electrons pass along a chain or electron carriers and the energy released is used to synthesis ATP.
3. Light has also struck PSI and a pair of electrons has been lost.
4. These electrons, along with protons (produced at PSII by photolysis of water), join NADP, which becomes reduced NADP.
5. The electrons from the oxidised PSII replace the electrons lost from PSI.
6. Electrons from photolysed water replace thos lsot by the oxidised chlorophyll in PSII.
7. Protons from photolysed water take part in chemiosmosis to make ATP and are then captured by NADP, in the stroma. They will be used in the light-independant stage.

right thats photophosphorylation done

hope this helps as it's as detailed as i can go, took an age to type aswell :P