Chapter 19: Photosynthesis Flashcards
Describe the structure of chloroplast
The chloroplast has an outer membrane and an inner membrane just like the mitochondria. It has stacked structures called thylakoids and in the thylakoid membrane is where the coupled oxidation-reduction reaction occurs. The stroma is where the dark reactions occur.
What does photoinduced charge separation mean?
Photoinduced charge separation is when an electron is excited from the ground state into a higher energy orbital and instead of the electron falling back to its original orbital and the energy used as heat, there is an acceptor that will take an electron from the excited state which creates a negative charge on the acceptor and a positive charge on the initial molecule.
What is a reaction center?
The reaction center is located in the thylakoid membrane and it is where the charge separation takes place within each photosystem.
How do accessory pigments assist in photosynthesis?
Accessory pigments are useful in photosynthesis because they allow the usage of other wavelengths besides just 680 and 700. They collect the photon and send it through a antenna complex which will take it to the reaction center where it can be used to excite an electron.
How does P680+ of photosystem 2 get reduced?
It extracts electrons from water molecules at the water-oxidizing complex. Absorption of a photon powers the removal of an electron from P680–>P680+ and then tyrosine will give up an electron to make P680 and then the tyrosine will take an electron from manganese (the water molecules are bound to this complex).
Manganese is in this position because it has multiple oxidation states and it forms strong bonds to oxygen.
It takes 4 photons to remove 4 electrons and form 1 water molecule.
What is the path that electrons take from P680* to cytochrome b6f complex?
The flow of electrons from P680*(excited state) is as follows:
-P680*
-Chl alpha
-Pheo alpha
-Qa
-Qb
-Q
-Cytochrome b6F (uses Q cycle to pump H+ into the thylakoid).
-Pc (plastocyanin)
-P700 (oxidized)
-P700*
What is the source of electrons to reduce P700?
Plastocyanin is where P700 oxidized will obtain its electrons to go to P700 reduced in order to be excited to P700*.
Describe the difference between cyclic and non-cyclic electrons.
-Under what cellular conditions do each occur
-Where does the path of electron differ between the two?
The difference between cyclic and noncyclic electrons is that one will use electrons in a cycle for some purposes while the other will send them in a linear path to their final destination.
Cyclic pathway:
-Q pool gives its electrons to cytochrome b6F and then they are given to plastocyanin.
-After plastocyanin, P700 is oxidized and then P700 is excited to P700.
-P700 gives its electrons to a series of accceptors before it gets to Fd.
-Once the elctrons are on Fd, the electrons are sent back to the Q pool to produce more H+ and more ATP.
Non Cyclic pathway:
-The same pathway but instead of the electrons from Fd going to Q pool, they are able to go to NADP+.
Describe regulation of photosynthesis.
ATP synthase is regulated by the oxidation or reduction of the disulfide bond. Fd is reduced and can then reduce Thioredoxin and then reduced thioredoxin can reduce ATP synthase to its more active form.
Describe the Jagendorf experiment.
-How was it done?
-What were the results?
-What do these results mean?
Jagendorf put a thylakoid with a pH of 7 into a buffer with a pH of 4. He then allowed the thylakoid to get to a pH of 4 and then placed it in a buffer with a pH of 8.0 along with ADP and Pi added.
His results showed that thylakoids make ATP and that H+ goes out of the thylakoid through ATP synthase.
This means that there is directionality of ATP synthase in photosynthesis. H+ is pumped into the thylakoid and ATP is pumped out into the stroma.
Describe the synthesis of ATP from the proton gradient.
A proton gradient is produced as H+ gets pumped into the thylakoid and as the gradient is formed the same methodology is used where there is a Fo and F1 subunit of ATP synthase and ATP can be generated .
It also needs to be in the reduced form to be efficient. In the oxidized form it has a disulfide bond which makes it slow. This can be reduced by thioredoxin but not until thioredoxin is reduced itself.
If there is lots of NADPH and a high H+ gradient, Fd(red) will reduce thioredoxin and that will reduce the disulfide bond allowing ATP synthase to be activated.
What is the benefit of e- going back to the Q cycle after Fd?
This is beneficial because there will be more H+ pumped into the thylakoid to make the gradient and more ATP will be synthesized.
What are the two options for electrons after the Fd step?
Q pool or NADP+.
