Flashcards in L19 + 20 photosynthesis Deck (45):
What is solar energy captured and converted to?
Chemical potential as ATP and NADPH
What are ATP and NADPH used for after the light has been converted to them?
To convert cO2 to sugar phosphates (and then carbohydrates)
What is the net reaction of photosynthesis?
CO2 + H2O ----> (CH2O) + O2
What drives the oxidation of water and the reduction of CO2?
Solar energy. Which is converted into ATP and NADPH
Which electrons pass through the electron- transport chain?
The electrons from water oxidation
What else are the light reactions known as?
The light-dependent reactions
What are the light reactions?
-Electrons from the H2O oxidation drive the formation of a protein gradient. The gradient is then used to make ATP.
(the chemiosmotic synthesis of ATP)
- Electrons from H2O oxidation eventually reduce NADP+ to NADPH
-O2 is by-product of water oxidation
What does oxidation of water lead to?
Reduction of NADP+ to NADPH
O2 as a by-product
What are the dark reactions also known as?
The light-independent or carbon-fixation reactions
What are the dark reactions?
Reduction of gaseous CO2 to carbohydrate
Requires reducing power and energy- which is provided by NADPH and ATP
What are photosystems I and II?
Pigment-protein complexes that contain many proteins and pigmnts embedded in the thylakoid membrane
What are the pigments in PSI and PSII?
Chlorophyll and carotenoid
What are electrons conducted by in the photosystems?
From H2O bound in PSII to NADP+ bound in PSI
WHat are PSII and PSI linked by?
Cytochrome b6f complex (a third non-pigmented protein complex)
What is light captured by and where is it trapped?
Captured by antenna pigments and transferred among themselves until it reaches the special-pair chlorophyll molecules. The special pair acts as an energy trap.
What is the Z scheme?
Shows th electron transfer steps in their redox potential. The more positive the redox potential (v), the lower on the graph it is. (P680 = +1.0, is at the bottom of the graph)
What is the main order of complexes in the z scheme?
H20-oxidized---- P680, P680*--> cytochrome bf complex---> P700, P700*. then goes down the slope until it turnds NAD+ to NADPH
What is the order of the PSs?
PSII then PSI. wrong way round with cytochrome bf complex in middle
What does the absorption of light do to P680 and P700?
Light converts the chlorophyll dimers P680 and P700 (poor reducing agents) to P680* and P700* (good reducing agents)
After releasing their electrons are P680* and P700* good reducing or oxidising agents?
Good oxidising agents
What is recombination in photosynthesis and why is this bad?
The electrons are attracted to go back to P680 which is inefficient. The system has evolved so that less than 1% does this.
In the pH gradient in photosynthesis, what is more acidic, the lumen of the stroma?
The lumen. pH difference of 3 units.
What is photophosphorylation?
Sythesis of ATP which is dependent upon light energy
What does chloroplast ATP synthase consist of?
Two major particles: Cfo and CF1
CFo spans the membrane, forms a pore for H+
CF1 protrudes into the stroma and catalyzes atp synthesis from ADP and Pi
How many protons move through chloroplast ATP synthase for 1 ATP to be made?
3 protons --> 1ATP
In the z scheme, for every 4 electrons transferred to 2nadph, how many protons are moved across the membrane and how many ATP are made?
8H+ moved across
2-3 ATP made
For each CO2 fixed, how many NADPHs and ATP are required?
2nadph and 3 atp needed
What is cyclic electron transfer around the b6f complex thought to generate?
An extra proton for every electron extracted from water
In the absence of Co2, what happens to electrons generated by PSI?
They can be recycled through the b6f complex to maintain energy (ATP) production.
Makes more ATP to be able to fix CO2
What do the dark reactions convert?
What are the dark reactions powered by?
ATP and NADPH
Where do the dark reactions happen and how?
In the chloroplast stroma by the reductive pentose phosphate cycle (RPP cycle) or Calvin cycle
WHat are the 3 main steps in the Calvin cycle?
1. fixation of atmospheric CO2
2. reduction of CO2 to carbohydrate
3. regeneration of the molecule that accepts CO2
What does ribulose 1,5-biphosphate carboxylase oxygenase (rubisco) do?
The first enzyme in the calvin cycle. Takes the CO2 and the 5 carbon sugar ribose and forms 2 3-carbon molecules. (3-phosphoglycerate)
Why is rubisco inefficient?
It's slow and poorly sleective. Binds to O2 sometimes instead of CO2 which wastes lots of energy. Rubisco has to be present in very high levels- most abundant protein on the planet.
When is rubisco acitve and inactive?
active in the light. inactive in the dark
What do plants convert RPP assimilated carbon into?
1. sucrose- in cytosol
2. starch- in chloroplast
3. cellulose- in cell wall
In photosynthesis does the lumen or stroma have more H+?
How many electrons do you need before you have enough oxidizing power to produce oxygen?
What does PQ do in photosynthesis?
It is like UQ in respiration. carries the electron from P680 to the plastocyanin attached to the cytochrome bf complex (carries a pair of electrons i think)
How many electrons do you need before you have enough oxidising power to produce oxygen?
What does PSI do to NADp+?
reduces nadp+ to nadph
What does PsII do to water?
oxidizes 2H20 to O2 and 4H+ (on the lumen side of the membrane)
Where is plastocyanin?
Attached to cytochrome bf complex in between the photosystems. Transfers electrons over P700