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58 Cards in this Set
- Front
- Back
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What is the main purpose of photosynthesis?
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-to reduce CO2 to the level of carbs using water as reducing agent
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What are the First Principles of Photosynthesis?
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1) must be a reduction
2) must be a biological reduction 3) must be a biological reductant 4) this reduction will require energy AND be regeneratable |
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Are photochemical reactions affected by temperature?
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-no, they're really fast no matter what
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Are chemical reactions affected by temperature?
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-yes, if you lower temp then required "dark" period becomes longer
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What was the purpose of the flash experiment?
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-to see optimal oxygen production
-occured over 100 ms or more |
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What occurs in a light reaction?
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-H+ derived from water is used in chemiosmotic synthesis of ATP
-Hydride ion (H:-) from water reduces NADP+ to NADPH -Release of O2 from splitting 2 water molecules |
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What occurs in a dark reaction?
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-reduction of gaseous CO2 to carbohydrate
-requires energy of NADPH and ATP |
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Can light and dark reaction occur at the same time?
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-Yes
-sum: CO2 + H20 = (CH2O) + O2 |
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What is the redox potential of NADP+?
How about the free energy? Wavelength of 680? |
- (-1.14V)
- +220 kJ/mol -175 kJ/mol |
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What is the equation for light energy?
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- E=hv
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What happened with the Red drop?
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-light was absorbed in the red-light spectrum but couldn't be used effectively in the far red wavelength
-if combined with shorter wavelength, more O2 is created than the sums of the two individualy -this supported the idea of two photosystems |
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What connects the two photosystems?
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-cytochrome bf complex
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How are electons conducted in the two photosystems?
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-conducted from water to NADP+
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Where are the proteins and pigmnets found for the two photosystems?
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-in the thylakoid membrane
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How many subunits are in Cyt. bf?
PSI? PSII? |
-4
-over 10 -over 25 |
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What is a reaction center in the photosystems?
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-The site of photochemical reaction in both PSI and PSII.
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What is a special pair?
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-two chlorophylls in each reaction center that are energized by light
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In PSI, what is the special pair?
PSII? |
-P700
-P680 |
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What is the Z-scheme?
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-path of electron flow and reduction potentials of the components in photosynthesis
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What does the Z-scheme do?
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-absorption of light energy converts P680 and P700 to excited molecules (from poor to good reducing agents)
-light energy drives electron flow uphill -NADP+ is ultimately reduced to NADPH |
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In PSII, where do the electrons for transport come from?
How are the electrons moved through Cytochrome bf? |
-oxidation of water
-catalyzed by the oxygen-evolving complex |
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What is P680?
P680+? P680*? |
-special pair pigment of PSII
-reduced by electron derived from oxidation of water -increased reducing power from light energizing |
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What happens with PSI energizing?
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-reduced P700 is excited to P700* which then donates an electron through a series of acceptors to ferredoxin (Fd)
-reduction of NADP+ by Fd |
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What catalyzes the reduction of NADP+ by Fd?
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-ferredoxin-NADP+ oxidoreductase (on the stromal membrane side)
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What is photophosphorylation?
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-synthesis of ATP which is dependant upon light energy
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What are the two major particles of Chloroplast ATP synthase?
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-CF0
-CF1 |
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Where is CF0 and why?
How about CF1? |
-CF0 spans the membrane, forms a pore for H+
-CF1 protrudes into the stroma and catalyzes ATP synthesis from ADP and Pi |
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What does cyclic electron transport yeild?
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-ATP but no NADPH
*thus balancing the need for 3 ATP for every 2 NADPH |
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What is the difference in cyclic electron flow in terms of ferredoxin?
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-Fd donates e- back to the PQ pool via a specialized cytochrome (instead of NADP+)
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How does cyclic flow increase the protonmotive force?
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-increases it
*also increases ATP but no NADP+ is produced |
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What powers Dark reactions?
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-ATP and NADPH (formed during light reactions)
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Where do dark reactions occur and in what cycle?
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-chloroplast stroma
-reductive pentose phosphate cycle (RPP cycle) |
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What are the three basic steps of a dark reaction?
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1) fixation of atmospheric CO2
2) Reduction of CO2 to carbohydrate 3) Regeneration of the molecule that accepts CO2 |
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What is the net equation for the RPP cycle?
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3CO2 + 9ATP + 6NADPH + 5H20 yields 9ADP + 8 Pi + 6NADP + Triose phosphate
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What does Rubisco stand for?
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-Ribulose 1,5-Bisphosphate Carboxylase - Oxygenase
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What is Rubisco?
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-makes up about 50% of soluble protein in plant leaves
-one of the most abundant enzymes in nature -8 large and 8 small subunits |
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What does Ribulose 1,5-bisphosphate create with CO2?
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-2 molecules of 3-phosphoglycerate
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When is Rubisco active?
Inactive? |
-in the light
-in the dark |
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What causes activation of Rubisco when in the light?
What inhibits it at night? |
-CO2, MG2+, and correct stromal pH
-2-Carboxyarabinitol 1-phosphate |
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What is the RPP cycle also known as?
What are the three stages of the RPP cycle. |
-Calvin Cycle
1) carboxylation 2) reduction 3) regeneration |
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What catalyzes carboxylation in the RPP cycle?
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-Rubisco
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What happens in the reduction stage of RPP cycle?
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-3-phosphoglycerate converted to glyceraldehyde 3-phosphate (G3P)
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What happens in the regeneration step of RPP cycle?
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-most of G3P is converted to ribulose 1,5-bisphosphate
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At night, how is the RPP cycle regulated?
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-oxidation of surfaceexposed -SH groups on some RPP enzymes inactivates them, preventing CO2 assimilation
-catabolism of starch via glycolysis and TCA cycle provides energy |
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How is RPP cycle regulated in daytime?
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-Thioredoxin is reduced by photosynthetic electron transpor
-reduced thioredoxin reduces disulfides to -SH, activating some RPP enzymes -Stromal Mg2+ and pH increase as protons translocated into lumen, activating fuctose 1,6-bisphosphatase and sedoheptulose 1,7-bisphosphatase |
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Rubisco aids carboxylation 70% of the time. What else can it be used for?
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-it uses O2 to catalyze an oxygenation reaction which competes with the carboxylation reaction (photorespiration)
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Is oxygenation better than carboxylation?
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-no, it is 1/3 to 1/4 of carboxylation
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What does photorespiration consume?
How about produce? |
-NADH, ATP
-glyoxylate, serine, glycine, and CO2 |
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What occurs in oxygenation (write names rather than formula)?
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-Ribulose 1,5-bisphosphate catalyzed by Rubisco to form one molecule of 2-phosphoglycolate and one molecule of 3-phosphoglycerate
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What is a benefit of photorespiration?
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-it salvages 3/4 of carbon that would normally be lost
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What is the C4 pathway?
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-C4 plants use this to ensure only carboxylation occurs and never oxygenation
-it uses a 4 Carbon sugar -uses ATP to bring 4 carbon sugar into cell and drop it directly next to Rubisco ensuring it gets used -splits in space (close to rubisco) |
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What is CAM?
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-Crassulacean acid metabolism
-found in succulents and helps conserve water in dry climates -splits in time |
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What is the initial product of carbon-fixation in C4 plants?
Where does this occur? |
-oxaloacetate
-mesophyll cells |
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What is a similar feature of both C4 pathways and CAM?
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-both can run with stoma closed
-both form oxaloacetate and then malate |
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What happens to the malate in C4 plants?
Then what? |
-it enters bundle sheath cells and converted to CO2, Pyruvate, and NADPH
-CO2 enters Calvin cycle, pyruvate enters mesophyll cells and reacts with ATP to regenerate starting material |
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What happens in CAM plants?
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-CO2 fixation occurs at night when stoma are open
-fixed into oxaloacetate which is converted to malate and stored in vacuoles -in daytime, stoma close and stored CO2 is removed from malate and put into calvin cycle |
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Why are C4 plants said to be split in space?
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-all Rubisco occurs in bundle sheath cells and occurs with or without stoma open (usually closed)
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Why are CAM plants said to be split in time?
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-CO2 fixation only occurs at night
-it is stored as malate until daytime when it converts it to energy for growth and CO2 production |
